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View Full Version : My mechanic: Even re-jetting will not eliminate all the popping



Magnificentbastard
02-10-2015, 5:48 AM
Wonder how you guys feel about this, I highly respect and like my mechanic, the guy is breathing bikes, was a (I believe) semi professional racer until he came off and broke like a hundred bones in his body and he is currently considering taking the leg off since it seems not to heal after a year or 2 wityh pins and rods sticking out of it, the guy is seriously righteous and also enjoys the respect of many if not all bikers in Ireland.

Today I called him since I had a bit of an odd issue coming up.
I had the bike in last weekend to get my front Tyre changed (go go white walls) and when I was ripping home on the motorway I had the odd feeling that I was running out of fuel, felt exactly like it throttle was kinda choking.
So I changed lanes to slow down and switch to reserve but then the engine kicked back in and I rode another 10k or so before at a traffic stop it cut out and I had to switch to reserve.

The cut the exhaust a few month ago and there is but only one baffle chamber left, a dino test showed no issues at all apart from being ever so slightly running lean, I never had any performance issues either.

The bike however pops like crazy when reducing speed, I asked him if a re-jet will get rid of the popping and he said it will slightly reduce it but never get rid of it!!

First Time I heard that - I always thought you can get rid of the popping sound all together?

BTW: bike is a Vstar 650 and I was going max which is 160 kmph going home when the issue happened.

Supertjeduc
02-10-2015, 6:06 AM
Frozen carbs ?

jethro57
02-10-2015, 6:31 AM
check timing

crush1776
02-10-2015, 7:03 AM
With an open exhaust, or nearly so with one chamber left as you state, he may be right. The engine was designed to run with some back pressure, remove the back pressure and you need to rejet. You may be able to jet it out completely, maybe not. He's an old racer, even a perfectly tuned race bike will pop if you are in full flog mode and slam the throttle closed. You can also check for intake leaks and vaporlock to rule those out.

Magnificentbastard
02-10-2015, 7:09 AM
I hear all of you, remember Dino showed no problem what so ever! apart from running very very little lean

goofyfoot2001
02-10-2015, 7:13 AM
Restrict the air with the mix screw. What's happening is you have too much oxygen available in the exhaust stroke and it's igniting unburnt fuel in the hot pipes. A technique well known to Vulcan 750 owners as Emissions control jap style.

You can certainly get rid of the popping.

Magnificentbastard
02-10-2015, 7:17 AM
Restrict the air with the mix screw. What's happening is you have too much oxygen available in the exhaust stroke and it's igniting unburnt fuel in the hot pipes. A technique well known to Vulcan 750 owners as Emissions control jap style.

You can certainly get rid of the popping.

you mean cherry popping (or what ever its called) it? as in a screw with a round open shape at the end installed on the inside of the exhaust?

goofyfoot2001
02-10-2015, 7:49 AM
No at the carb. But now that you mention it, you could also have a leak in the exhaust pipe right at the engine.

loddytoddy
02-10-2015, 8:50 AM
check the valves? my xs popped on deceleration and when I pulled the motor apart the valves weren't seating tight on the exhaust side...

Magnificentbastard
02-10-2015, 9:00 AM
No at the carb. But now that you mention it, you could also have a leak in the exhaust pipe right at the engine.

Well, I got rid off the Air introduction system, I plugged the holes as recommended here http://www.650ccnd.com/ais.htm 1) with a golf tee, for the small hose 2) the other hole with 9mm shell. Both are super tight I believe.

goofyfoot2001
02-10-2015, 10:32 AM
Even so, you have to adjust your air mix screws. That is where you will eliminate the pops. ON the Vulcan unscrewing was restricting the air and screwing in was giving it more. You should do it at operating temp and just ride up and down the street till ya get it right.

What it comes down to is your fuel air mix. When you get that right, your pops go away. So you may have to change jets with the new pipes. I think your mechanic is wrong on that one.

Westboundbiker
02-10-2015, 10:48 AM
By the way, I did the same as you, and had the same issue. Messing with the needle and jets helped a lot. Look on Mikuni's site for a lot of good info.

Also, its dyno, not dino, just fyi.

Magnificentbastard
02-10-2015, 11:28 AM
By the way, I did the same as you, and had the same issue. Messing with the needle and jets helped a lot. Look on Mikuni's site for a lot of good info.

Also, its dyno, not dino, just fyi.

you are right lol looked weird when I wrote it

Westboundbiker
02-10-2015, 12:35 PM
Do you have the GAK mod on your bike too? (Pods) I found that it still takes some tuning from what he sends to get it running well. I know I was reading about eliminating backfiring somewhere... I'll see if I can't find it again and post it.

Pendulum
02-10-2015, 12:45 PM
I'd check for air leaks between the carb(s) and head as well as between the exhaust and head, and maybe do a leak down test. If all that looks good, and the dyno tuning went well, I'd say your mechanic is right.

I had an XS650 that I could never get to stop backfiring... I didn't dyno test it, but we did plug chops for days and the carbs were DIALED. Ran awesome, plugs looked good... And it still back-fired. I even added a muffler, thinking the short pipes were the problem, and it still did it but a bit less.

Supertjeduc
02-10-2015, 3:10 PM
What temperature was is when this al happend.?
Carbs can freeze at low temperatures

Wolfie
02-10-2015, 6:43 PM
Jap bikes made after 1986 were notorious for running way too lean (to meet US emissions)....adding the shitty CVK carbs compounded issues....V-twins are mostly prone to the decel "pop"....
If you opened your exhaust, match it by adding pods...and like Goofyfoot said, you need to make the air/fuel mixture richer.....

What size and brand carbs are on it ?....single carb ?...dual carb ??.....if its a single carb, throw a 38mm Mikuni on it and be done....

Wolfie
02-10-2015, 6:45 PM
...PS...tell yer mechanic that an old fucker building bikes since the late 60s says he's full of shit....lol....

Magnificentbastard
02-11-2015, 7:12 AM
Got some more info.

The bike is .3 - .5 running lean from 2000 - 4000 RPM which is when I go slow, so no issue, but that explains of course the banging
4000 - Top is no issue, so happy days.

My plan is as follows.

1) Wait until we have better weather give or take 2 month.
2) Going to ride the bitch down to his shop.
3) Going to take the whole exhaust off (the fat part so only the stumpy parts are left) which means the pipes are open
4) Run Dyno see how bad it is
5) Get it re-jetted
6) Ride it home
7) Weld on cool exhaust tips

goofyfoot2001
02-11-2015, 7:37 AM
2 months! Shit, I'd flip out. I expect maybe this is the last week of this shit you guys keep sending south and then it's summer.

Wolfie
02-11-2015, 6:43 PM
How much you payin that asshole son ???....that fucker's laughin all the way to the bank when he see's ya coming !!!....lolol...

I used to tournament bass fish (yeah, Bassmasters)....this clown reels bait out to ya bro, then you gladly take the bait like some dumbass brim....if yer dumb enough to pay a dealer, dunno what yer doin here...everybody here does their own shit....

PS...I'd LOVE to shoot the shit outta yer avatar btw, lol...sorry....nuthin personal, but I hate yuppies....

This has got to be one of the top 10 on CC in awhile....

datadavid
02-12-2015, 3:13 PM
All these expert tips and noone mentions carb synch..
if you skip all the previous bs posted and synch your carbs i bet you 50 of whatever your local currency is That your poppelipopping will vanish.
I also bet you the same amount that you could not perform a carb synch even if your life depended on it.
Google that shit!

Magnificentbastard
02-13-2015, 7:28 AM
Thank you all!

Wolfie
02-14-2015, 7:17 PM
noone mentions carb synch..


Because theyre is no need to do a carb sych on that bike.....only bikes with more than 2 carbs need it....even bikes with duals really dont...

Nottso
02-14-2015, 10:04 PM
Is it a soft popping sound almost like "burbling" for lack of a better word or is it a loud "bang" or "crack" sound like a firecracker? If it's loud and sharp, look for an exhaust leak at the head, any of the slip-joints, or even a cracked pipe. When air is introduced inside the exhaust, it allows the unburned fuel vapor in the pipe to ignite.

JBDad85
02-15-2015, 10:25 AM
Because theyre is no need to do a carb sych on that bike.....only bikes with more than 2 carbs need it....even bikes with duals really dont...

I disagree...at least with this model, having the carbs synch'd makes a big difference in performance. Anytime I do anything to change the exhaust or intake, I synch the carbs after i get the air/fuel mixture dialed in. The 650 v star runs like shit if they are out of synch.

datadavid
02-16-2015, 2:00 AM
My bad, didn't even bother to look up the model, assumed it was a dual carb twin.
And anyone who thinks carb syncs are not important does not know shit.
But of course, obviously you dont sync single carbs.
Edit: googled that shit - its a twin carb bike Wolfie.
So if you have lots of popping on deceleration syncing will probably take care of it.
If it started suddenly while riding and was ok before its probably not a jetting issue.

Mocnyang
02-17-2015, 11:52 PM
I may be missing something but in the first post you said something about setting your petcock to reserve and the motor kicked back in then stalled at a stop light and you had to put it back in reserve. Clean the petcock.

If it was running fine before and now it's not with no changes then something's got some dirt in it

FYI....I know nothing about this type of bike and I could very well could not have comprehended this post.

Helped a guy once roadside on a freshly built honda cafe bike stalled and he had been messing with it for 30min, basically he ran out of gas and never switched to reserve.

Mocnyang
02-19-2015, 11:15 PM
Thank you all!

Did you get it fixed yet???

Magnificentbastard
02-20-2015, 4:50 AM
Did you get it fixed yet???

No brother not yet, I am living in ireland and weather was shite in the last few days, I also don't have a garage so I need todo all work myself.
I see what I can do this weekend but I am also having a rideout with the green knights wehoooo.

Jetblack
02-20-2015, 5:30 PM
So you haven't re-jetted eh?

Which of the following combinations apply to you?

1. Stock jets, open pipes & pods
2. Stock jets, restricted pipes & pods
3. Stock jets, restricted pipes & stock filter(air box)
4. Stock jets, open pipes & stock filter(air box)

and... any emissions shit with any combination of the above too?

Wolfie
02-21-2015, 5:14 PM
And anyone who thinks carb syncs are not important does not know shit

Really....ya, ok....lol....I been doin this shit since the late 60s....tunin flat track bikes too...try using a fancy tool to "synch" dual Amals from 1970....all ya need on a dual carb is to make sure the slides are opening at the same time....and that aint "synching"....thats a cable adjustment...
As for the air/fuel mix screws, ya set them according to the condition of the plugs...

Buddy of mine spent 3 days tryin to synch his 4 carb KZ 1000...paid big bucks fer the fancy tool...I went over there and had it done manually in 1.5 hrs....he said it was best itd run since he got it...
Sure...these tools can come in handy...for those who dont know shit, ahem....and have the extra bucks to buy em....just sayin, that for a 2 carb setup, its not absolutely needed....IMO, better to learn the old school methods first, and then use what yer comfortable with....too many rely on all the new, modern shit, and the old ways are bein forgotten....I try to teach as many as are interested, the old ways...am I wrong doin that ?...No....but just like everything else....sword and knifemakeing for example...once the old ways are lost, its near impossible to bring em back....

....btw.....I HAVE a dual carb v-twin...no fancy ass tools needed....waste of money....better spent on beer or gas....

Jetblack
02-21-2015, 7:23 PM
I personally recommend a sync on 2+, makes tuning easier... though you can tune around it like wolfie says, it's a fucking process though to keep plug chopping til you get it right.... when they are out of sync as the mixture screws will be way different in the end.

Here's a 100% free no special tool required way to sync by yours truly:

http://www.chopcult.com/forum/showthread.php?t=25532

and our fix a fucked up carb all in one thread:

http://www.chopcult.com/forum/showthread.php?t=33716

Cheers! Don't be a dick.

Westboundbiker
02-21-2015, 10:15 PM
There's also this option, which is a true sync, and I've done it before, on my V Star
http://www.650ccnd.com/mano.htm

junkman
02-24-2015, 9:20 PM
First, remove the AIS system on the bike. Most of the popping will go away. I used .45 shells to block the passageways.

AIS Removal Instructions:
https://sites.google.com/site/vstar1100kb/home/5-modifications/1-ai

Then open up the air fuel mixture screws on the carbs. It is likely running lean because of the opened up pipes. Too lean and ya run the risk of blowing a hole in a piston. Lean produces power but produces heat that weakens the piston. Its a fine line. Open the mixture screws 1/8 turn at a time from where they are now. If ya already messed with them, gently turn them all the way in, dont torque em down just all the way in til you feel resistance. Then back them out 2.5 turns. start the bike and see how it runs, take it for a spin. If ya don't like how it runs, back them out 1/8 turn. Start it, ride it and see where yer at. Repeat the 1/8 turn. The mixture screws are a bitch to get to. I gave up and replaced mine with aftermarket long head mixture screws.
Like these:
http://www.maxairengineering.com/mm5/merchant.mvc?Screen=PROD&Product_Code=MPS-PRO
OR an alternative:
https://sites.google.com/site/vstar1100kb/home/tuning/pilot-mixture-screws


If it still runs rough, synch the carbs. Properly synched carbs makes a bike purrrrrrr


I have 3 VStar 1100's that I have done many mods including open pipes, pods and re-jet.

This link has a ton of info on the VSTAR. A lot of it is 1100 based, but it still applies to the 2 cylinder 650.
https://sites.google.com/site/vstar1100kb/home

Jetblack
02-25-2015, 6:53 AM
^solid... a note about a/f screws, pilot screws, mixtures screws whatever word you wanna use for them... always screw them in counting turns til they gently seat and back them out to the new turn... every time. Doesn't matter if its a 16th of a fucking turn, in then back out. dont know turns? think of a clock face. 12 is start all the way around to 12 again? 1 turn. 3? a 1/4 6? 1/2 9? 3/4.

why seat them first? those tiny ass lil o-rings and washers can hang on your ass fucking up flow... hence fucking your mixture and tune.

datadavid
02-25-2015, 7:29 AM
I use a pair of nails for adjusting amals.
im sorry im not old as fuck sir, but engines run better and pop less on decel with "synched fucking carbs" agreed?
I sure have respect for elders, if it goes both ways..
No respect for bald bitter old condescending a-holes though! 😆
And i basically only know old school ways since my fat bald condescending asshole father taught me most of what i know.
Now lets play nice shall we?