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View Full Version : GS650 Air/Fuel/Spark issue



NickPapageorgio
05-26-2010, 1:33 PM
Ok, here's where I am.

1982 Suzuki gs 650. I have just about got this baby running perfectly, but I'm getting a sputter at certain times. I can lay into it in 1st, no problem. Second is fine up until about 6-7K. 3rd, 4th & 5th are ok if I am just barely in the throttle at all. If I give it any throttle past just cruising it chokes up and sputters non-stop, i.e. doesn't clear up.

Fully rebuilt from the case up. New plugs. New wires. Freshly rebuilt carbs (broken down completely, soaked overnight, cleaned & reassembled) Checked the spark in neutral at each cylinder with a spark tester and it looked solid through higher rpms. Everything sitting on the ground in neutral looks like it should be running fine.

The only thing I can figure is I'm only running half my airbox. Due to space issues after I chopped the frame, my battery is in the way of running the front half of the airbox (the section with the filter). I have the second half that runs into the intake boots, and I made a metal cover for the open side of the box. The cover has holes drilled in it to allow air to flow and a piece of filter foam material between it and the box.

Could that be causing the problem? If so, why would it only do it at higher rpms in 2nd, 3rd, 4th, 5th? Any answers are appreciated because at this point I'm kind of stumped.

Has anyone with a similar GS had any success in deleting the airbox entirely? How should one go about that if it's possible?

WOMPY
05-26-2010, 1:49 PM
Sounds like you may have to go down a notch on your float needles. Check color of plugs right after a high rpm run. What carbs are you running?
You said spark is fine, but try this if all else fails: add a standard 30A relay to the coils to ensure 13.8 volts are going to the coils at all times. Here's a link to help with that:
http://www.wgcarbs.com//index.php?option=com_content&task=view&id=12&Itemid=26

NickPapageorgio
05-26-2010, 1:57 PM
Running the stock carbs. Looking at the plugs is interesting. 1 & 4 cyl. are black. 2 & 3 cyl. are EPA lean looking (white, brownish tint). Thanks for that link, will definitely give it a read.

hanshan29
05-27-2010, 1:32 PM
Hey, I've had the same problem after I pulled the air box off my GS. Have you rejetted the carbs for the new airbox style? If you modify the intake or exhaust on a GS at all, expect to rejet and retune the carbs. They're extremely sensitive. I'd suggest deleting the airbox entirely and getting k&n pod filters and a jet kit for your setup. Don't know if DynoJet has them or you just have to fiddle and tune till you get it right. Basically if you change the flow of air at all you're going to have to rejet/re-tune. It's a hassle, but once you get them right they run forever. Also be sure to get the carbs balanced if you haven't done that already as well. I have the pre-EPA carbs now on my '77 GS400 and I had the EPA carbs on my '83 GS550 and they were both ridiculously sensitive to any change despite what the manual may say about the EPA carbs.
Just my 2 cents, I'm no mechanic, but I have a little bit of experience with these GS's. I had my '77 rebuilt last year and it took me quite a while to dial it all in. I rejet when I put on shorter mufflers and again when I put on the pod filters and I'll have to do it again when I put on the 2 into 1 exhaust I'm saving up for. Hope it works out for you, good luck.

shop102
05-28-2010, 6:10 AM
i would run some filter pods for sure. Do you have ports for a carb sync???

NickPapageorgio
05-28-2010, 8:42 AM
Thanks for the replies so far guys. I really do appreciate it.

I think I'm actually going to do most of the things suggested here and see where I end up. Going to go with the dyna ignition, pod filters and float needle adjustment and see where that puts me first.

Also, yes it has the carb sync ports on the intake boots. We're going to do that as well.

I'm still learning a lot. Over the past year and a half, I've gone from knowing absolutely nothing other than where to put the gas and oil to where I feel like I can "ALMOST" rebuild an engine from the bottom up. I'll get there eventually. There really is no other feeling like taking something that is ready for the junk heap and making it rumble again. I may be hooked...

Sighless
05-28-2010, 9:18 AM
I have an 81/82 GS450. Did you replace the original rectifier? They had an issue with those, they're wrong for the bike and will eventually fry your charging system.

READ THIS --> http://www.electrosport.com/technical-r ... _56350.php

But that may be part of the problem, not getting propper spark.
When you cut the air box where did you put the filter? When I first got mine back together I had my filter to close to the carbs, and once I hit 45 or got to far into the throttle it would bog out, sputter and all but die. I remove the foam from my stacks and replaced it with some VERY fine stainless steel screen, imediate improvement. Rejetting might help

Here's a TON of info for th GS series of bikes.
http://www.thegsresources.com/

Her's a shitty walk through of my build.
http://www.metricunderground.com/forum/viewtopic.php?f=6&t=953

hanshan29
05-29-2010, 6:26 AM
I have an 81/82 GS450. Did you replace the original rectifier? They had an issue with those, they're wrong for the bike and will eventually fry your charging system.

READ THIS --> http://www.electrosport.com/technical-r ... _56350.php

But that may be part of the problem, not getting propper spark.
When you cut the air box where did you put the filter? When I first got mine back together I had my filter to close to the carbs, and once I hit 45 or got to far into the throttle it would bog out, sputter and all but die. I remove the foam from my stacks and replaced it with some VERY fine stainless steel screen, imediate improvement. Rejetting might help

Here's a TON of info for th GS series of bikes.
http://www.thegsresources.com/

Her's a shitty walk through of my build.
http://www.metricunderground.com/forum/viewtopic.php?f=6&t=953




Agreed, forgot about Suzuki's attempt at electrics on the early '80's GS's was garbage. My '83 550 blew the regulator/rectifier and that took out the CDI box and good luck replacing that in my neck of the woods. No more made and no aftermarket ones. They cycle salvage around here was perfectly aware of the problems though and were willing to sell me what I needed for a grand.LOL Nearly twice what it's worth brand new of course.

The GSResources is a great place just don't mention your chopping it!

NickPapageorgio
05-30-2010, 7:41 PM
Update:

Ran velocity stacks and this thing is absolutely screaming now. I had grown so accustomed to the spitting I almost wasn't ready for it when I opened it up lol. I took her out on the road and 1st gear just felt more...alive I guess is the word. I thought, "hmmm..." Nailed it the rest of the way thru 5th and I was ready to let out of it before she was.

F.Y.I. you guys working on shoe string budgets like me, and I don't know if it's like this for all GS models, but it's worth a look if you're looking to run something similar. The rubber mounts that went from my air box to my carbs were actually just mounted in the air box via the rubber channel in this pic. Once I pulled them out, little did I know they'd make such cool looking stacks. They have a metal retainer clip on the inside that worked perfectly to clamp in some round cuts of an old T-shirt for a temporary filter. I'm going to find some hard screen material and form 4 of them for the insides of these.

Sighless
05-31-2010, 12:35 PM
Update:

Ran velocity stacks and this thing is absolutely screaming now. I had grown so accustomed to the spitting I almost wasn't ready for it when I opened it up lol. I took her out on the road and 1st gear just felt more...alive I guess is the word. I thought, "hmmm..." Nailed it the rest of the way thru 5th and I was ready to let out of it before she was.

F.Y.I. you guys working on shoe string budgets like me, and I don't know if it's like this for all GS models, but it's worth a look if you're looking to run something similar. The rubber mounts that went from my air box to my carbs were actually just mounted in the air box via the rubber channel in this pic. Once I pulled them out, little did I know they'd make such cool looking stacks. They have a metal retainer clip on the inside that worked perfectly to clamp in some round cuts of an old T-shirt for a temporary filter. I'm going to find some hard screen material and form 4 of them for the insides of these.


I used the stock screen out of the air box. it has 2 layers so I used tin snips and cut 'em to fit added a super fine SS screen. figured it's 30 plus years old and still looks good, so I used it (because I'm a cheap bastard)

NickPapageorgio
05-31-2010, 3:45 PM
I used the stock screen out of the air box. it has 2 layers so I used tin snips and cut 'em to fit added a super fine SS screen. figured it's 30 plus years old and still looks good, so I used it (because I'm a cheap bastard)

Nice! As soon as I press the submit button I'm going to see if there's any of that screen in my air box lol. I've been looking a couple places for steel mesh today.

This place looks like they'll make discs from 5mm - 600mm. Not sure on minimum quantity or anything, I haven't contacted them yet. Here's the link anyway: http://www.shengfa-wiremesh.com/metal-products/wire-mesh-discs.html

This one I bookmarked cause they sold them in smaller sheets. 12" x 12" @ $14 as opposed to a couple sites I found today that had minimum orders of $75 and up: http://utahbiodieselsupply.com/stainlessmesh.php

Also, for anyone interested in searching for it yourself, the search terms I had the most success with were "dutch weave steel mesh" and/or "micron steel mesh".

jskilly123
01-26-2011, 10:47 AM
After doing this modification did you have to retune carbs?

turtlem1969
02-07-2011, 6:11 PM
still waiting on whether or not you had to re-tune the carbs.

Sighless
02-09-2011, 12:48 PM
On my GS 450 I did not have to do anything more than go up 3 sizes on my main jets. BUT I have tall velocity stacks and long pipes (with thumb screws for back pressure) . I hear that a lot of people have problems with removing air boxes on these bikes. I'm not sure if all Zuki had this; but the air adjuster screw is covered with a plug and has to be drilled out to get at them (mine are this way on my 81) last I had heard Nick had the bike up and running with minimal tuning. I'm sure mine could use a little fine tuning (when I get out into the mountains it struggles at times; but so do most carburated bikes)
turtlem1969 what years is your Zuk? I'm guessing by the forks it's late 70's, if that's the case it has different carburetors(VM, not cv). my current project is a 78 and those carbs are VERY sensitive to cleanliness. I finally got mine running good (right before I started chopping) henryinva, on here, makes some SICK gs750 as well.

cntrhub
02-09-2011, 1:37 PM
http://www.shengfa-wiremesh.com/images/products/wire-strainers-5.jpg

http://www.shengfa-wiremesh.com/images/products/brass-wire-mesh-3.jpg


still waiting on whether or not you had to re-tune the carbs.

After doing this modification did you have to retune carbs?

This is a cool thread. Here is my deal. Will I have to rejet? No. It's all about air speed. So, I take my strainer, mold it over a velocity stack and now I have a big closed gasket that looks the V-stack. I now take my gold mesh and with some glue that is removable so it bends; Not paint that chips. I then close it down.

I have that glue that can take on gas like a kreem in a tank kind of layer over the gold mesh till the lag goes away. The more you close off the mesh screen, the slower the air, the more it matches that air box kind of speed signal.

Hey, Thanks! I'm INN like a stale beer to an al co haul lick that glue and sniff her too is my nose the rub beer applicator.

ape
02-10-2011, 6:10 AM
just a fyi when you remove the t-shirt material from the carbs and replace it with the mesh the bike will run diffrent and you will need to rejet the carbs you can get a simple hand drill set to do it for cheep and it's not hard at all just start at the bit that is just a tad bigger than the jet put it on and see how it run's! it can take a few time's of on and off but its a great learning exp. and also if you are having uneven burn issues with your plugs after the rejeting you might want to check your air mix adjustment,

also I like the stack's man! whats the whole bike look like?

turtlem1969
02-10-2011, 7:28 AM
Sighless- the one I have pictured is an '82 model with the cv's, had to put that one on hold due to titling issues, currently chopping out a '79 gs750, I'll try to get some pics of it posted when i get the time. Was going to swap the 82 motor into the 79 frame but coming up with some issues on that, a little bit more involved then what i want to mess with right now.

shaft
04-19-2011, 8:29 PM
Hey, I've had the same problem after I pulled the air box off my GS. Have you rejetted the carbs for the new airbox style? If you modify the intake or exhaust on a GS at all, expect to rejet and retune the carbs. They're extremely sensitive. I'd suggest deleting the airbox entirely and getting k&n pod filters and a jet kit for your setup. Don't know if DynoJet has them or you just have to fiddle and tune till you get it right. Basically if you change the flow of air at all you're going to have to rejet/re-tune. It's a hassle, but once you get them right they run forever. Also be sure to get the carbs balanced if you haven't done that already as well. I have the pre-EPA carbs now on my '77 GS400 and I had the EPA carbs on my '83 GS550 and they were both ridiculously sensitive to any change despite what the manual may say about the EPA carbs.
Just my 2 cents, I'm no mechanic, but I have a little bit of experience with these GS's. I had my '77 rebuilt last year and it took me quite a while to dial it all in. I rejet when I put on shorter mufflers and again when I put on the pod filters and I'll have to do it again when I put on the 2 into 1 exhaust I'm saving up for. Hope it works out for you, good luck.

What size jets did you get for your gs and where? I have pod filters and am planning to slash the pipes? Any suggestions?