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GS750es Carb problem???? I'm stumped!!

  • Thread starter Thread starter rvnkvn
  • Start date Start date
R

rvnkvn

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My 83 GS750es has stock exhaust, Uni pods, 700 cams, 700 pistons. I'm using the 700 carb's with the bigger jets than the 750 had.

Goes like heck under acceleration, but had a POOR idle and a ocassional pop through the exhaust. It REQUIRES me to blip the throttle at a stop, or jack up the idle speed up to keep it running when I'm not going down the road.
I have cleaned the carbs, set the floats,changed the plugs,ran some seafoam through the carbs, removed the plugs to adjust the pilot air screws at 3 turns out. Getting TERRIBLE gas mileage, and it is starting to run alot better,just wont idle or cruise smoothly.

I had pulled the plugs,1,2,3 were black, but 4 seemed like it was light tan. replaced all of them with new, and started to notice that the 4 cylinder exhaust was not as hot as the other 3 were. So I changed coils, and cleaned off the pick up on the right side of the engine. Geting better but NOT good enough.. ANY thought or things to try or check would be greatly appreciated....
 
What kind of voltage are you getting at the coils?


Are your pods new, clean and lightly oiled?
 
Exact same issue on my 700, I have yoshi exhaust, K&N pods and jet kit as well. After living with having to blip the throttle at every stop for years, I finally fixed it by giving it an extra screw or two at the pilots.

Try 4-5 turns out, hell 6 or 7 if it doesn't work. It's free.
 
niclpnut said:
have you checked the valve clearances recently and synced the carbs?
Click to expand...

Yeah, what he said. :dancing:

Also, there is more to setting the mixture screws than just "3 turns out." Once you've set valve clearances and synch'd the carbs you needs to set each pilot mixture screw on it's own for the proper amount of mixture for that cylinder.

I'm not up on what carbs are used on that bike but setting each mixture screw for highest idle seems like a common procedure.

Chris
 
Valves were checked and adjusted after the rebuild. I'll check on voltage at the coil, but wouldn't #1 be suffering also since it's on the same coil?

If the bike wont idle, do i raise the rpms up enough to smooth out the idle with the pilot screws and then set base idle?

Pods are new uni-foams. oil is very light. I have not sync the carbs yet..
 
Last edited:
Intake boot o-rings. These bikes cook them.

I know from experience, having suffered the exact same symptoms twice now on my 700. The first time, I went crazy cleaning carbs, messing with the ignition and the coils, plug boots, etc.... Changed out the intake o-rings and Voila! idle was fixed.

The scond time, I didn't bother with anything but the intake o-rings. Fixed it again.
 
Unless I rolled on out of the groves, these were all replaced with new ones from the gasket kit....
 
No, that remains the same between the 700 and the 750 carbs...Do you think that would make that difference???
 
Have you messed with the idle mixture screws at all? If you can't get it to idle richening these then I'd go up one on the pilot jets.
 
You're talking about the ones under the plugs in front of the carbs correct?.. I had turned those out about 4 times, and seemed to be getting better. Still wont idle and bucks and surges at low to medium cruise...Kevin
 
You will need to shim the needle or get a Dynojet needle with the pods.
That's why your bucking and surging at take off.
If you can get to redline on the main that's good.
Get the needle dialed in next.
Then get the idle straight.
If the idle mixture screws don't help get a bigger pilot jet.
 
Thank You!!.. finally something I can do myself to resolve this problem. How and what do you use IF you shim the needle without buying the dyna kit?
 
Actually, you can't do any idle/low speed tuning until you have synch'd the carbs.

All of your tuning depends directly on vacuum supplied by the cylinder. With the carbs out of synch you aren't getting consistent vacuum to each carb and you will just be chasing your tail trying to tune them.

You said you did the valve clearances. That's good. Now do the synch. Only then can you start tuning the low speed mixture supply.

Chris
 
Thanks Chris... I'm getting really good at pulling carb's off the bike. I'll work on that tonight after work. I'l also double check the remaining intake o rings.
 
You should vacuum synch the carbs on the bike while it is running. Bench synch'ing is what you do with the carbs off the bike to try and get them close enough so the bike will run well enough to do a proper synch with either vacuum gauges or a manometer.

Chris
 
My trick is clamping one and two on just a little bit then levering on three and four into the boots. Taking them off is the easy part. Only good thing about pods.

The screws I'm talking about are the ones on top between the carb body and cylinder. They're hard to adjust, but a small glasses screwdriver works ok. Just lift the back of the tank. I use a flashlight to check orientation of the slot in the screw, turn it a bit, and check again to make sure I'm turning them all evenly. That's good enough until I sync the carbs.

Just start it again after every adjustment, see if it idles. Like others have said, no point in adjusting for highest idle until after you've synced the carbs.
 
Curly said:
My trick is clamping one and two on just a little bit then levering on three and four into the boots. Taking them off is the easy part. Only good thing about pods.

The screws I'm talking about are the ones on top between the carb body and cylinder. They're hard to adjust, but a small glasses screwdriver works ok. Just lift the back of the tank. I use a flashlight to check orientation of the slot in the screw, turn it a bit, and check again to make sure I'm turning them all evenly. That's good enough until I sync the carbs.

Just start it again after every adjustment, see if it idles. Like others have said, no point in adjusting for highest idle until after you've synced the carbs.
Click to expand...
I adjusted mine with the middle sized flathead screwdriver on my Leatherman. Just the right size! :rolleyes:
 
So, I'll pull the carb's ,bench sync the throttle blades, and set the pilot air screws to 3 turns out, install back on the bike and fine tune the screws per cylinder to get the best vacumme signal.... After I get this sorted out, shim the needle ,possibll change the main and pilot jets. GOT IT!

Thanks everyone!!
 
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