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jthomasbtm
05-29-2015, 9:16 PM
I built this 1976 cb750. Can't figure it out. Running keihin carbs, pod filters, straight pipes, dyna coils and electronic ignition. Fully rebuilt engine. The bike will start up and idle fine, but as soon as it's given throttle it cuts, misses and dies out. I've tried everything the Clymer says and can't figure it out. I need to get this thing on the road. Any advice is greatly appreciated.

https://youtu.be/xFr9U9nX6tE

There's a video of it being a shit bag. Tell me what you guys l think or what to try.

jthomasbtm
05-29-2015, 9:36 PM
By the way I suspect it's a carb issue but I've tried everything I know. I'll pay someone in as much beer as you want if you can come make this run. Literally cases upon cases upon cases.

JetBlackII
05-30-2015, 2:32 AM
Sounds like it is idled really high, do you have the choke out or in?

JuanCarlito
05-30-2015, 3:45 AM
I feel your pain! Maybe we can burn our bikes together?

jthomasbtm
05-30-2015, 5:04 AM
Choke was out when it started then I pused it off.

Freewheeler
05-30-2015, 10:42 AM
It sounds nice, there's a lot of power there - can't be a lot wrong.

Sounds like fuel starvation to me, i.e. kinked fuel line or maybe a blockage in the fuel cap breather.

What sort of condition is the fuel tap in, is there good fuel flow from it? is the bowl at the bottom of the tap fuel of rust?

Or have you tried all of the above already?

Nick

gs650
05-30-2015, 1:14 PM
What size jets are you using? From what I've been reading and experiencing, its really hard to get them to run right with pod filters. Sounds like yours is running out of gas but with the stock jetting it will not run right with the pods. Velocity stacks are supposed to be much better than pods but I haven't tried them yet.

deathmetaldan
05-30-2015, 1:59 PM
its for sure a fuel/air thing. Its always a fucking cunt, especially when you do pods and pipes at the same time and have no baseline of how far up you have to go.

Freewheeler
05-30-2015, 2:33 PM
its for sure a fuel/air thing. Its always a fucking cunt, especially when you do pods and pipes at the same time and have no baseline of how far up you have to go.

Indeed. What baseline did you work against or was it running ok with the same setup before you rebuilt the bike?

It it was running ok before using the same setup then something has been misplaced during reassembly - as I say, kinked hose, sediment in the tank stirred up during reassembly, idle screw settings for instance.

If its a brand new setup then its a tuning issue and you would need to get some guidance on what pipes, filters and jets will work well together.

The other thought I had was that my old Honda 4 did used to take a while to warm up and would die if taken off the choke too quickly.

Just a few thoughts that might not be in your manual.

Nick

jthomasbtm
05-30-2015, 4:40 PM
Steady fuel flow from the tank to the carbs. I pulled the plugs last night after this was posted and they were fouled completley black so I'm assuming too much fuel.

jthomasbtm
05-30-2015, 4:41 PM
I can't remember exactly what size jets I'm running, but I'll check it out. I thought it was a jetting issue but don't know what size to run or a good place to get them from.

jthomasbtm
05-30-2015, 4:45 PM
I had the motor running in the stock frame/setup for about a day and then pulled the motor so I don't really have a base to go off of. I know it's something with fuel and air delivery/mixture but not sure how to go about getting it set right. It'll fire right up but when I put it in gear and try to pull out it sputters out. Carbs are my worst nightmare on any bike.

gs650
05-30-2015, 11:12 PM
There is lots of info on tuning for pods on the SOHC forum. Your bike has a different style of carbs than my bike but from what I found out 2 sizes bigger on the pilot jet and 3 sizes bigger on the main jet will get you close.

mcclane
05-31-2015, 2:53 AM
You Must der the needles in the sliders higher; and check the high of the float gauge

Freewheeler
05-31-2015, 6:29 AM
Steady fuel flow from the tank to the carbs. I pulled the plugs last night after this was posted and they were fouled completley black so I'm assuming too much fuel.

It's starting to sound like that isn't it?

That's a good point made about the float height as well - also worth checking the floats aren't ruptured or split and do actually float.

Also, it would be really helpful to make notes on jet sizes, number of turns on idle screws and such and how it ran with those settings - I always found it so much easier to refer back to notes that relying upon my memory.

Don't worry, we will get you there :)

Nick

CarloFreeze
05-31-2015, 10:42 AM
Let's figure this out. Tell me which Keihin carbs you are running and we'll get them dialed in. Float heights are important. If you have the carbs with the spring clips, that's good because you'll be able to drop the bowls pretty easily. You may have to pull them to change things depending on what you've done.

Don't start messing with jetting or changing needle positions just yet, in order to get it right, you have to start with getting it to idle properly, everything else for tuning is useless unless you get that right.

Now stock sizes and setting for the jetting on the "roundtop" carbs is 40 idle jets, needles in the middle position, and usually 105 main jets. These numbers will probably change, but it's better to change little things at a time. Make sure you have the baseline things working first. The jetting of the midrange and main jets doesn't matter at idle. You should start with your air mixture screws at 1 turn out on each carb. Float levels on the carbs are measured at 26mm from the notch just above the gasket surface. This is the most important. You have to make sure you get that part right.

Here's a great visual guide.

http://www.hondachopper.com/garage/carb_info/float_levels/float_levels.html

Crowe138
05-31-2015, 8:08 PM
Done this over n over again jetting cb750 chops. If you had stock jetting in there before then it's definently gotta change or will run totally wack with pods n straight pipes. It is possible to get it right tho so don't give up . The idle jets stock are #40 n that's usually good at 1 turn out on pilot screws or one size bigger if you can't get the idle good with all the wide open stuff ur runnin, the mains gotta go up almost 4 sizes most the time. That means you need to get something between 120-130 on the main jets( Kiehin main jets in that number range go up in weird increments usually by 5) lotsa of sites online sellin whole sets of mains for cb750's , honda dealers will have them to but usually expensive.

Also double check that the coil wires were put on the right cylinders (long lead coil is for the outside cyl. 1 & 4 , short lead coils for the inside 2 & 3) when it was put back in the frame and make sure the centrifugal advance behind the ignition plate isn't sticking or broken n double check timing with a timing light should be idling on the "F" mark. You can feel the pipes to right after it starts up to make sure all cylinders are firing if u got one or two cold pipes u got a problem due to ignition or fuel, don't burn your hand, good luck

jthomasbtm
05-31-2015, 10:02 PM
I'm gonna swing over to the garage after work and check all these things and I'll let everyone know about everything as soon as I get there. Thanks for the help guys.

Freewheeler
06-01-2015, 1:35 AM
I'm gonna swing over to the garage after work and check all these things and I'll let everyone know about everything as soon as I get there. Thanks for the help guys.

I cant wait to hear!

Nick

JuanCarlito
06-01-2015, 6:51 AM
I cant wait to hear!

Nick

Yea me too. Following your thread hoping to figure out my own 650 issues. Test run after work today. . . .gonna be a long 9 hrs lol

CarloFreeze
06-01-2015, 7:24 AM
The other thing to do when you take the carbs off is to make sure you bench sync them so that all the slides are at the same height when no throttle is applied. Once you get them dialed in jetting and setting wise, you can vacuum sync while the bike is running with a set of gauges and really see how smooth the engine gets.

All the carb tuning info you need is right here. http://www.hondachopper.com/garage/carb_info/carb_info.html

Also, like Crowe 138 said, mark the position of your ignition plate with a Sharpie at the screw holes. Pull the plate off and lube the spark advancer if you haven't done it already. It's important that it doesn't stick because it can cause a hanging high idle if it sticks at full advance.

This is what it looks like with the points plate removed. Just pull it off the shaft and lube the cam with some white grease and reinstall. There are small springs that allow the lobes to open up, make sure these slide freely as well.

60671

jthomasbtm
06-01-2015, 6:21 PM
So I went to the garage after work, pulled her carbs and brought them home. Pulled them apart and the slow jet is a number 40 and the main is 110. Float height is at 26mm. Throttle needle is on the dead center notch. Screws were 1 turn out. A few people said they thought I needed bigger jets, but would that be the case since the plugs are fouling out? That's the info I have right now, let me know what you guys think.




These are the carbs I'm running. Well trying to.

http://i61.tinypic.com/21oxcht.jpg

These are what the plugs look like.

http://i60.tinypic.com/dzbhno.jpg

Sky
06-01-2015, 7:29 PM
Suck, squeeze, bang, blow. All in the right amount at the right time. If your having trouble tuning, better rule out mechanical issues before continuing.
Sooty plugs can be an indication of weak spark. You said the ignition is new? Are you running the coils recommended by the ign manufacturer? 12 volts at the coils? Wires, plugs and gaps? Don't forget good grounds for all electronic components.
I'd start with making sure the ignition timing is statically correct, and that the advance unit (if present) is moving freely.
Double check your compression, and a leak down if low comp is indicated. Valve timing is paramount, cam chain timing ok?
Intake leaks and/or worn slides will foil any fuel metering.

jthomasbtm
06-01-2015, 8:19 PM
I'm using, dyna coils and electonic ignition. Getting 12 volts at the coils, all the wiring is new and good, leads and plus are new and plugs are gapped correctly.timing is set, compression is really good, and I believe cam chain timing is good.

CarloFreeze
06-02-2015, 12:10 AM
Okay good, it sounds like you have the ignition side of things pretty set. There's nothing to time with the cam chain unless you did a top end job and changed anything there. Right now you are basically at the stock settings for those carbs. I run the same ones. You may find yourself changing those needle clip settings and main jet sizes once you get the bike running right at idle, but let's do one thing at a time. In your video it sounds like all 4 cylinders aren't firing but it could just be the pipes. I guess double check that the ignition is wired correctly to the coils. Yellow = 1 & 4 cylinders, Blue = 2 & 3 cylinders. A reversal there would make the timing fire all strange. Did you check the spark plug caps? They should be NGK 5K ohm resistor types. Make sure they are all showing proper resistance by sticking one meter probe in the plug side and the other probe where it screws onto the coil wire. Should be +/- 20% from 5000 ohms. What plugs are you using as well? The factory manual recommends NGK D-8ES or Denso X24ES-U. I actually prefer the Denso's after trying both types, but NGK D-8's are easier to come by.

Go through these steps and report back. I wish I could say it was easier to come help in person, but you're about 4 hours away from me haha.

Crowe138
06-02-2015, 9:33 AM
You're seeing slightly sooty plugs now but haven't got past quarter throttle so I wouldn't take it as to solid info yet on jetting, 110 is likely to small to get a good transfer from the low range to mid range with straight pipes and pods, pick up 120 , 125 , & 130 main jets.
The plug can be sooty from using the choke to start it or from it still not getting up to running temp since your not able to really get a good ride, also if you put new rings in then they will still be seating and reading won't be extremely accurate at this point. Like sky said , weak/intermittent spark can also cause the plugs to look like that, the plug boots could have to much resistance (super common on old cb750's) retarded ignition timing , stuck centrifugal advance, and excessive exhaust valve gap or to tight of an intake valve gap. Visually confirm your sparks good on at least one or all of the outer and inner cylinders if you haven't yet should be crisp blue spark.

turtlem1969
06-02-2015, 8:03 PM
One thing not yet mentioned- check your carb to intake boots, if they are loose or cracked or not sealed tightly they will give off all sorts of weird readings and make it run like crap when the right hand is twisted.

jthomasbtm
06-04-2015, 4:55 PM
The ignition wiring is good and I'm using dyna boots and leads along with dyna coils. The plugs are also gapped to spec. It was firing on all 4, while the bike was running all the pipes were hot.

jthomasbtm
06-04-2015, 4:56 PM
I get a super bright blue spark from every plug. That's what I initially thought when this was happening. Still trying to figure this out.

jthomasbtm
06-04-2015, 4:58 PM
All the boots are good and cranked down tight.

jthomasbtm
06-04-2015, 5:03 PM
http://i61.tinypic.com/vmy8md.png

Anyone ever fuck around with one of these? Get rid of this 4 carb problem. Haha

deathmetaldan
06-05-2015, 5:59 AM
http://i61.tinypic.com/vmy8md.png

Anyone ever fuck around with one of these? Get rid of this 4 carb problem. Haha

you think you have tuning problems now? Get one of those lol

CarloFreeze
06-05-2015, 10:07 AM
That picture of the carb rack you showed looks like you have the air mixture screws (the flathead recessed one on the lower left) socked all the way in? Also that vacuum intake screw (mashed Phillips screw on the top right) has been changed and those need to be full seated or else you'll have airleaks there. The purpose of those screws are so you can remove them and install vacuum ports for hooking up a set of sync gauges when tuning.

Maybe I'm crazy but were you turning out the wrong screw for air mixture? I mean if you were turning the vacuum port screw (which should be fully seated) out 1 turn and leaving the air mixture screw socked down tight, that could explain that weird high idle at start up that dies. I'm just trying to figure out what's wrong here.

This is a shot of my carbs and you can see that the air mixture screw on carb #4 is about flush the edge of the hole at 1 1/4" turns out.

60823

Hotel
06-05-2015, 8:47 PM
Had this problem on a 83 shadow. Great on idle, cutout with throttle. Take masking tape and tape all the way around half of the pods to restrict air and try it like that. What have you got to lose.

500 miles later, still riding with tape around mine.

jthomasbtm
06-06-2015, 5:26 PM
I set my screws to what you have yours set to, and I'm gonna try it tomorrow when I get to the garage. I'll let you know. And hotel, I'll try that as well. Sounds like it makes sense. Thanks dude

Hotel
06-07-2015, 10:19 AM
I hope it works!

jthomasbtm
06-07-2015, 12:37 PM
I threw the carbs on, taped up the pods abs the fucker made it up the road! It's still missing a bit but I think it's timing related. I'm uploading a video of it running, I'll post it once it uploads.

Hotel
06-07-2015, 1:25 PM
Awesome! Glad to hear it went down the road. You may have to restrict more/less with the tape and fine tune the carb. I got lucky, when I taped mine up she was close, only problem being I cut out in high RPMS, but for normal scooting around I don't hit those rpms anyhow so I haven't bothered.

CarloFreeze
06-07-2015, 1:25 PM
Pods are a little tough because they don't use a velocity stack like a stock airbox and the air is pulled into the carb differently. Doesn't mean they can't work. Air restriction is key, tape will get you there.

jthomasbtm
06-07-2015, 2:17 PM
https://youtu.be/uQyOza6zcBc

There's the video, you guys tell me what you think. Like I said, I think the timing needs messed with because it's still idling really high and missing at throttle, but hey, the fucker runs.

Hotel
06-07-2015, 3:21 PM
Closer than you were!!
Cool looking scoot. I think the stepped headlights like you are running look like shit normally, but on that long rake, it just fits perfectly.

jthomasbtm
06-07-2015, 3:59 PM
Thanks dude. I'm gonna try and get to the garage after work tomorrow and see if I can dick with that timing. I'll report back on what happens.

Freewheeler
06-07-2015, 4:11 PM
That is GREAT news!

Idling too high would usually require an adjustment at the throttle stop screw or the twist grip - assuming all carbs are set correctly and synced.

My advice would be to get the idle set correctly before hunting the misfire, a good idle could eradicate it.

Really pleased to see your progress - are you a little more comfortable with carbs now?!

Nick

Freewheeler
06-07-2015, 4:14 PM
Also, did I just see a plunger rear end on your bike?

Nick

jthomasbtm
06-07-2015, 4:28 PM
I synced the carbs and adjusted the idle screw on the carb rack. I'll check it out tomorrow though and give it a look over. And yeah, I've had those carbs apart so many times I can visualize every little part. Haha. And yeah that is a plunger frame. Got it for free so I decided to run it instead of hardtailing a stock frame.

CarloFreeze
06-08-2015, 8:05 AM
Hey. Good to see you got it rolling around! As far as syncing goes, when bench syncing, I like to use a 1/16" drill bit and stick it under the slide of one carb inlet. That's a good minimum opening which would mock the amount a carb would be open while idling with no throttle. Pick any one carb and use the idle screw to bring the slide down enough to just "kiss" the drill bit so that you can slide it in and out of the carb throat with a little bit of resistance. Then match all the other carb slides to the same height. That's all there really is to it without getting into vacuum syncing which is just another step to make the individual carbs match to their cylinder.

With this method, it'll ensure that you have enough adjustment to bump the idle up or down to where it needs to be to hold idle at around 1000 rpm. When it's right with timing and ignition, you shouldn't really have to bump the idle screw more than a 1/4" of a turn or so except maybe when cold starting.

Freewheeler
06-08-2015, 11:31 PM
Hey. Good to see you got it rolling around! As far as syncing goes, when bench syncing, I like to use a 1/16" drill bit and stick it under the slide of one carb inlet. That's a good minimum opening which would mock the amount a carb would be open while idling with no throttle. Pick any one carb and use the idle screw to bring the slide down enough to just "kiss" the drill bit so that you can slide it in and out of the carb throat with a little bit of resistance. Then match all the other carb slides to the same height. That's all there really is to it without getting into vacuum syncing which is just another step to make the individual carbs match to their cylinder.

With this method, it'll ensure that you have enough adjustment to bump the idle up or down to where it needs to be to hold idle at around 1000 rpm. When it's right with timing and ignition, you shouldn't really have to bump the idle screw more than a 1/4" of a turn or so except maybe when cold starting.

Good tip.

Nick

JuanCarlito
06-08-2015, 11:48 PM
Good tip.

Nick

I was having a similar problem (79 CB650), able to start up and idle but as soon as I cracked the throttle it died out. Major things I did - bench sync the carbs using the drill bit method. Adjust the fast idle screw (on mine between 2 and 3 carb) and set the idle screw to barely touch the throttle mechanism then I adjust from there after start up. Re jetted to a 118 main and a 38 slow. Checked and made sure the accelerator pump was adjusted and working, and set idle screws to 1.5 out . . . . All this just improved the idle but I still had the problem. Then I took a members advice and marked that plate where you adjust the timing (can't remember name) with a felt pen at the 3 screws...pulled it off and cleaned and lubed the automatic timing unit found behind said plate. Mine was seized right up. After cleaning and lube I put it all back together placing the plate where I had marked (hoping the timing was right lol) and put everything back together. Bike fired up as normal BUT this time I had awesome throttle response!!! Took her for my first ride beyond my road, hit the highway and opened her up. After my ride I checked my plugs and they are all a nice tan, well except 1 is sorta rich. My point is I had the carbs off and taken apart so many times and tried so many settings and changes and the whole time it was a 15 minute clean and lube job that was needed. If you haven't checked the ATU yet I would suggest it for sure! And the fast idle screw, not the one you adjust by hand but the one with the lock nut etc . . . If your carbs have that? I have no clue lol

CarloFreeze
06-09-2015, 8:13 AM
Juan, his carbs don't have a fast idle screw. Lubing the timing advancer plate is a good tip which was suggested already. I think he's getting closer!

jthomasbtm
06-09-2015, 4:28 PM
Yeah, I don't have an idle screw except for on the carb rack, I'll try lubing the advance tomorrow and report back. Finally have a day off work, gonna try and get that fucker buttoned up. Thanks to everyone. I'll keep you all posted.

CarloFreeze
06-09-2015, 8:11 PM
You have to remove the ignition plate to get to the advancer so make sure you mark it's position beforehand.

JuanCarlito
06-09-2015, 8:48 PM
You have to remove the ignition plate to get to the advancer so make sure you mark it's position beforehand.

Definitely!

And I was just throwing out ideas before CarloFreeze. Trying to help. Not familiar with his carbs thats why I said "if"

CarloFreeze
06-09-2015, 9:52 PM
It's all good.

jthomasbtm
06-10-2015, 3:28 PM
Cleaned and lubed the atu. Made no difference. Still doing the same thing. I'm lost. Haha

CarloFreeze
06-10-2015, 5:09 PM
Have you checked the timing with a light?

jthomasbtm
06-10-2015, 6:01 PM
Yeah I checked with a timing light. Hard to tell if it's right because I don't have a tac to check the rpms.

hogvibrator
06-10-2015, 7:00 PM
sounds like jetting to me .i did a 750 twin with open pipes and pods did the same,so after jetting it to death still wouldnt run right,so i put baffles in from dennis kirk and rejetted ,after 3 days of playing with it i went three on idle and three on main bigger.

jthomasbtm
06-10-2015, 7:16 PM
That's what I've been thinking. Where did you get the jets from?

CarloFreeze
06-11-2015, 12:07 AM
Jetting is something you'll get into when you have the timing right. You have to get the spark right or else changing carb settings will get you nowhere. It's the basic factors of combustion, AIR, FUEL, & SPARK. You know the carbs are clean and the jets are at stock positions. You don't need a tach to set the timing. Your dyna ignition plate has a window to shine a timing light into to see where the timing should be at for the 1-4 cylinder and the 2-3 cylinders. Run the bike and check with a light. It shouldn't matter if it idles high for now. It's possible that you have the timing too far advanced and that's what is causing some issues to begin with. Ultimately the bike should idle regardless of jetting. Then you start getting into air/fuel ratios and that's where the jets and needle clip settings will start to factor in.

Follow this set of instructions. It's not exactly the same since you don't have points, but the procedure is pretty much the same.

http://www.hondachopper.com/garage/carb_info/timing/timing1.html

Freewheeler
06-11-2015, 12:48 AM
Jetting is something you'll get into when you have the timing right. You have to get the spark right or else changing carb settings will get you nowhere. It's the basic factors of combustion, AIR, FUEL, & SPARK. You know the carbs are clean and the jets are at stock positions. You don't need a tach to set the timing. Your dyna ignition plate has a window to shine a timing light into to see where the timing should be at for the 1-4 cylinder and the 2-3 cylinders. Run the bike and check with a light. It shouldn't matter if it idles high for now. It's possible that you have the timing too far advanced and that's what is causing some issues to begin with. Ultimately the bike should idle regardless of jetting. Then you start getting into air/fuel ratios and that's where the jets and needle clip settings will start to factor in.

Follow this set of instructions. It's not exactly the same since you don't have points, but the procedure is pretty much the same.

http://www.hondachopper.com/garage/carb_info/timing/timing1.html

+1

You've made great progress in the last week or so - keep going!

Nick

jthomasbtm
06-13-2015, 1:04 PM
I was messing with the bike again on Thursday after work, pulled the carbs off to check a few things and realized that the intake boot on carb number 4 was split almost the whole way down. I ordered a whole new set. They should be here today. Gonna give it a shot tomorrow, hopefully that was part of the problem.

CarloFreeze
06-13-2015, 6:44 PM
Well that'd certainly make a cylinder run like shit! Another thing to consider if the new boots didn't come with them, is to replace the clamps as well.

I had a similar thing happen on my bike because without a stock airbox the weight of the carbs puts all the stress on the boots. When you install the new boots, see how much the carbs move up and down. I ended up devising a way of supporting them in the back where the filters are with a little bit of safety wire looped around the carb throat and over the backbone.

When it comes to these things there is only so many things that can be wrong. If the carbs are rebuilt and synced up, timing is on and electrical is good, you shouldn't have a lot of problems. Tuning is pretty simple once the kinks are worked out.

Freewheeler
06-14-2015, 1:09 PM
I was messing with the bike again on Thursday after work, pulled the carbs off to check a few things and realized that the intake boot on carb number 4 was split almost the whole way down. I ordered a whole new set. They should be here today. Gonna give it a shot tomorrow, hopefully that was part of the problem.

Probably why its revving so high as well - too much air getting in there.

Must be close now?

Nick

jthomasbtm
06-14-2015, 1:33 PM
Just put the new boots on, it fired right up, still missing and idling extremely high. Put a timing light to it and it's dead on with timing. I have the idle turned down as low as it will go. Anyone wanna buy a 750? Haha

JuanCarlito
06-14-2015, 3:46 PM
Just throwing out ideas> But what kind of pods are you running? On my cb650 when I installed pods the little plastic 'fingers' that hold the choke cable would get stuck on the pods and it would cause the choke to stay stuck in the full position even if I pushed the plunger back to half or closed.This left me running very rich, high idle, and shit response. I had to modify the 2 inside pods slightly to allow clearance. Maybe worth a look??

Hotel
06-14-2015, 4:23 PM
With mine I made my own wiring harness from scratch and had some mix ups that needed to be worked out.
One being I never grounded my ignition (like an idiot).
But somehow it was tied into my clutch switch, with the clutch pulled in (giving ground) she would rev high. Release clutch and she would fall on her face.
After that point she was only good with no load (then taped up the pods and was good to go)
Point being, maybe something is overlooked in the wiring?
If not, I vote burn the bitch down.

CarloFreeze
06-14-2015, 4:25 PM
Well since you've gotten this far you must be close to it. I'm thinking of all the suggestions I can think of off hand. Are all the vacuum port screws installed and tightened? Check on Juan's suggestion. Take the pods off and check that the choke linkage is opening and closing all the flaps together with the choke lever. It is also possible that the pods aren't offering enough restriction and causing a lean condition. What brand are the pods?

You may have to work with the individual carbs air mixture screws. The 1 turn out thing is just a baseline and you have to adjust accordingly from there. Seeing as how you are running very little restriction on the intake side and none on the exhaust side, your high idle and misfiring is likely a result of a lean condition through out. Try giving all the air mixture screws an 1/4 turn in and report back. If it seems like the condition doesn't really change much, it may be ready to jump up to a larger size idle jet.

Here's a good source for jets. http://www.jetsrus.com

Since you said the timing is on and the fuel is flowing fine, you just gotta get the air part right. Stick with it, it'll be worth it I promise.

jthomasbtm
06-14-2015, 6:59 PM
I'm running the foam uni pods. I taped them up, ran a strip of duct tape from the back so only about 3/4 of an inch of each pod is open. All the vacuum port screws are tightened and in there. The choke is working properly I checked that right off the bat. The wiring is all good from what I can tell, I made the harness from a diagram on here and everywhere is getting power and the right voltage. I'll mess with the air screws as soon as I have time off work. If not I guess jets it is. I'm not sure if I mentioned this, but the engine was bored out to 863cc when it was rebuilt. Idk if that would effect anything.

Hotel
06-14-2015, 7:15 PM
Is your petcock gravity feed or vacuume. If vacuume, is it sucking hard enough to pull the plunger all the way to supply sufficient fuel? Is the plunger siezed?

jthomasbtm
06-14-2015, 7:18 PM
Gravity fed. I watch the fuel flow fast to the carbs.

Hotel
06-14-2015, 7:29 PM
http://i1302.photobucket.com/albums/ag138/Hotel/usa1297_zpsyfx5inah.jpg (http://s1302.photobucket.com/user/Hotel/media/usa1297_zpsyfx5inah.jpg.html)

jthomasbtm
06-14-2015, 7:37 PM
I'm not far from this happening.

Hotel
06-14-2015, 7:39 PM
We all deserve a few hours notice so we can join the bonfire.
But in all seriousness, I'll give it more thought. If I come up with anything, I'll be sure to let you know.

jthomasbtm
06-14-2015, 7:42 PM
Thanks dude. I'm out of ideas. Still trying though.

Freewheeler
06-15-2015, 6:55 AM
Just put the new boots on, it fired right up, still missing and idling extremely high. Put a timing light to it and it's dead on with timing. I have the idle turned down as low as it will go. Anyone wanna buy a 750? Haha

I know it doesn't seem like it but you are getting closer, get the idle sorted and then start chasing that misfire down.

Is your throttle fully closed at the twistgrip but still open at the carbs? Could be the cable is sticking, maybe its snagging somewhere. As you have four carbs you need to be sure that all slides are closed when the carb is off the bench and actually fitted - in my experience it can be quite easy to refit the carb slides such that one of the cables is tight, causing a slide to be partially open when the rest are closed - try taking the airbox out and inspecting the position of each slide as you open the throttle.

Come on,you are so close!

Nick

CarloFreeze
06-15-2015, 7:51 AM
Remember, you control the machine, not the other way around.

sdsbassist
06-16-2015, 11:30 AM
I've owned 4 or 5 Honda 750s. Do yourself a favor and get the stock airbox. At the very least this will help narrow down the issues. Another thing that was causing shitty idle on mine was that it was nuts on timing 1-4, and not 2-3. Check both. You may have the move the 2-3 banana on the dyna plate around a bit to get ti closer. Made a world of difference on the one I am currently dicking with...

Freewheeler
06-17-2015, 2:53 PM
The boys need an update, has Jthomas gone off to look for a box of matches and some gas or did he find an issue with the tight carb slide cables?

Nick

Hotel
06-17-2015, 5:52 PM
An update would be nice, I believe every logical angle has been approached and keep throwing out ideas would be repetitive.
I would put my money on it being something ridiciously simple that's just being overlooked.

jthomasbtm
06-17-2015, 6:59 PM
Sorry guys, I haven't had time to mess with it in the last few days. Got a few days off work and went on a long ride for a few days (not on the 750...) and a camping trip. Didn't mess with my phone much. But I'm gonna try and get out there tomorrow. I would have let you guys know if I got it going. Coincidentally when I got back I got a call from a guy and he offered to sell me 6, 750 motors for 600 bucks..... fucked if I buy them, fucked if I don't.

JuanCarlito
06-18-2015, 3:10 AM
I click on this thread daily to see if you've got it going yet lol. also I found myself on the net searching possible causes for your bike . . . Why? I have no clue lol Really hope you figure it out soon! And I agree with Hotel, it's probably something stupid simple thats just been overlooked while everyone searches for the bigger problem.

jthomasbtm
06-18-2015, 12:53 PM
Haha. I appreciate the help. I'm hoping it's something small, bit ive say and stared at it for 3 hours thinking of what it could be going through everything in my head but can't pick it out. Hopefully I stumble across it soon.

Crowe138
06-18-2015, 10:07 PM
Maybe the stock pilot jets are to small for the 836 kit , maybe the springs on the advance are worn out n making the idle uncontrollable seen that happen before

Hotel
06-19-2015, 5:32 AM
I'm going off memory of the thread here and ill try not to repeat any one else.
Have you pulled the choke cable out and verified that it is working as it should?
Maybe one is stuck somewhere causing that cylinder to be an individual.

Freewheeler
06-19-2015, 4:13 PM
I thought the jetting was all sorted and you've been through the carbs?

Are the thottle slides opening at the same time..?

Nick

jthomasbtm
06-21-2015, 8:54 PM
Crowe, I was thinking that about the jets and the springs on the advance seem to be springy. Hotel, I don't have a choke cable it's a lever, and they all open and close when it's moved.

jthomasbtm
06-21-2015, 8:56 PM
Everyone told me me to hold off on getting jets until I get it running. And I did go theory the carbs, more then a few times. I believe the slides are opening at the same time. I did a bench sync with a drill bit.

Freewheeler
06-23-2015, 4:40 AM
Everyone told me me to hold off on getting jets until I get it running. And I did go theory the carbs, more then a few times. I believe the slides are opening at the same time. I did a bench sync with a drill bit.

Ok, so you set it all up ok on the bench and have backed the idle screw down as far as it will go - I assume this is on the carb? Are you sure then that the throttle cable is not snagged somewhere thereby raising the idle? The idle screw will be ineffective if the throttle is partially open at the handlebar if, for instance, the cable is frayed and snagging somewhere.

Because I don't know what carb you are running, is there a separate cable for each slide or does the throttle cable pull on a bar or something that raises the slides in unison? If its the former then you need to be certain that none of the cables are tight or pulling on the slides before the throttle is opened - it is so easy to get this wrong after fitting.

Also I am assuming the throttle slides have been fitted correctly and are facing the right way.

Your problem is something simple - stick with it.

Nick

CarloFreeze
06-23-2015, 7:36 AM
Good suggestion Freewheeler. His carbs are attached to a rack with linkage and a cam that uses one cable to open all the slides together. The slides also only can go in one way because the carb bodies are notched as well as the slides.

Double check the idle screw and that it lets the slides all the way down like Freewheeler said. The throttle pull cable is worth checking. Pull the pods off while the carbs are on the bike and twist the throttle and make sure the slides pull up and come all the way back down to verify that everything is smooth and right. Maybe your throttle cable is adjusted too tightly? It should have a 1/4" of play at the handlebars.

If all these things are fine, it's time to start fucking with jetting. You can either buy the next bigger size for the idle jets or if you are frugal and have a decent drill press, you can pull the idle jets and drill them out to the next bigger size which would be 42, then reinstall and see how the idle is.

It's good that we've gone over everything else first before moving to this point. It's a pain on the ass at first, but if you can get a 70's CB750 dialed in, it makes everything else seem so simple down the road hahaha.

Freewheeler
06-23-2015, 1:29 PM
CarloFreeze and I should buy this bike and get between us get it running!

Nick

CarloFreeze
06-23-2015, 6:13 PM
Better yet, jthomas should fly us out and we'll get it running for him and he can buy us a nice dinner for being such swell guys.

jthomasbtm
06-23-2015, 11:37 PM
Get here on your own and I'll feed you and get you drunk as fuck. I work for anhauser busch. Unlimited beer. Haha. But I'll try the jetting. Maybe drill them out just to give it a shot. But no, the throttle cable isn't stuck and the slides are all moving up and down together. I found a company where you tell them what bike you're running, what air filter, pipes and a whole bunch of other specs on your bike (including town where you live and elevation) and they send you 4 different sets of jets to try for 80 bucks

Freewheeler
06-24-2015, 2:34 AM
Get here on your own and I'll feed you and get you drunk as fuck. I work for anhauser busch. Unlimited beer. Haha. But I'll try the jetting. Maybe drill them out just to give it a shot. But no, the throttle cable isn't stuck and the slides are all moving up and down together. I found a company where you tell them what bike you're running, what air filter, pipes and a whole bunch of other specs on your bike (including town where you live and elevation) and they send you 4 different sets of jets to try for 80 bucks

80 bucks sounds like a good deal and at least then you will know.

As Carlo said, anything after this should be easy - i'm very happy to have two cylinders on mine and will be even happier to have just the one on my next project.

Nick

JuanCarlito
07-02-2015, 1:27 AM
What!!!
My internet has been down for a week (country living) and the first day I get it back I come here to see whats been going on and . . . . nothing! No updates? I need to know man whats going on? Any progress? Did you figure it out and have just been riding instead of posting???

Freewheeler
07-02-2015, 2:41 PM
What!!!
My internet has been down for a week (country living) and the first day I get it back I come here to see whats been going on and . . . . nothing! No updates? I need to know man whats going on? Any progress? Did you figure it out and have just been riding instead of posting???

I'm of the same mind! I reckon he lost interest and hit the Anhauser Busch!

Nick

JuanCarlito
08-03-2015, 1:53 PM
Anything new?? Super curious still.

deathmetaldan
08-03-2015, 4:37 PM
maybe he has been too busy riding :)

fingers crossed

CarloFreeze
08-03-2015, 5:09 PM
Maybe he burned it to the ground and quit Chop Cult!

JuanCarlito
08-04-2015, 12:20 AM
maybe he has been too busy riding :)

fingers crossed

I hope so! But if CarloFreeze is right I hope he filmed it and posted on youtube so we can at least watch the mayhem!

CarloFreeze
08-04-2015, 7:47 AM
All the hippest bike burning videos are on Vimeo haha.

JetBlackII
08-04-2015, 5:46 PM
Are your fuel lines the exact same length? It's best to run one from the tank to the middle of the whole carb bank then make T's off of that to feed the carbs with hoses from there the exact same length... the cylinder(s) with the best compression of course, will suck the most fuel... but they can only eat as much fuel that exits the tank which is a limited amount... it would be a good idea to remove any stock tank vent spill prevention or drill out the air passages to larger on a cap to increase the amount of fuel flow.

Misfiring, is likely a bad plug cap or wire... they shouldn't be able to wiggle when seated on the plug either. You can unscrew the plug caps, make sure you have some excess and trim about 1/4 inch off the ends then twist the boots on the wire, don't shove or wiggle the caps onto the wire, make sure the plug wires are not touching any metal on the way to the plugs as well, the arc is so strong it can jump some energy through the wire in any spot right into the contact spot that is not the plug.

Sounds like you haven't really been into the carbs properly for a good cleaning/bench synch etc. from past posts... but if you have since those posts...