2 year fight

[pw1382]

OK guys, I have a problem. I picked up an 82 gs850 a few years ago. The bike was all together but needed a few small things, intake boots, coils, little stuff. The bike already had a 4-1 exhaust and a stage 3jet kit and was told the bike ran great.

Got the bike running after some new parts and a few well placed swings of a hammer but never running "right". It starts right up and idles great, Revs up fantastic but when you put it in gear and go down the road it breaks up in higher rpm. In lower gears it does it almost at read line but in high gears, it does it around 5000-6000rpm. But revs up great to that point and if you slowly role into the throttle at highway speeds (55-60) it will build a few more rpm's. It almost sounds like its hitting a rev limiter.


I pulled the air box off to see what happens and it runs much better at high rpm but crap at low so I thought it was running rich in the main. It had a 150 main to start (what comes with the jet kit) and I've backed it down all the way to factory 115 and nothing changed at all. Still acts the exact same way. I've been fighting this bike on and off for 2 years now and it's starting to get to me.

[Who Dat?]

A bit surprised that changing the jets did not seem to help. The 150 mains that come with the Stage 3 kit would be a bit much for just a pipe (no pods), I would suggest a Stage 1 kit. Going to stock 115 jets should have made it run a bit lean, so I am suspecting float levels. If a float is high (low numbers when setting), it will run richer than expected. If the floats are low (higher numbers when setting), there won't be as much gas in the bowls. In the lower gears, you will get to redline before draining the bowls, but longer times on the throttle in the higher gears might be draining the bowls. The floats are supposed to be at 22.4mm from the edge of the carb body (no gasket installed) to the bottom of the step on the float.

Have you read the plugs when it craps out like that? Hold the throttle for a while while it's messing up, then hit the 'kill' switch, pull the clutch, coast to a stop in a safe area. Pull the plugs and see what they tell you.

Pulling the airbox was a big hint. The reason it's running poorly at low speed is because of turbulent air trying to get into the carb mouths. The boots that connect the carbs to the airbox are actually velocity stacks inside the airbox, which smoothes out the airflow through the carb.

[JTGS850GL]

I'd start by checking the plugs and see what they look like. A few plug chops should give you a batter view on what's happening. You might also want to check the voltage going to the coils. Low voltage will cause the spark to break up just as you've described.

If you're using the stock air box with a 4-1 exhaust then I'd recommend going with a stock version K&N filter along with 120 mains and the needles raised using 3 washers in place of the stock plastic spacer. Leave the pilot, needle and needle jets stock. Adjust the enrichment screws to about 2.5 turns out. Should run great after that.

[raygun]

Does the mechanical advance work? If it's not advancing that could also be an issue at higher rpm.

[pw1382]

Update,

I pulled the carbs off and switched the mains over to 120s and now I have a huge vacuum leak. Think it's coming from the butterfly o rings. Got a full o ring kit on the way and we'll go from there. Can't do a dam thing with a leak like that.

I've checked the timing advance and all seams to be working fine and I've checked the voltage on the coils. All seam to be in speck. I've even trimmed the coil wires thinking it might have a little crud on the wire and didn't help any.

Hoping to have the o rings in this weekend and have the carbs back together. I'll keep you all posted.

Thanks, Preston.

[JTGS850GL]

Mind telling me what you mean by "butterfly O-rings" and why you suspect them? If you're talking about the shaft seals, then no O-ring kit will include those and they don't usually leak. If you really do have an air leak, then I'd start looking at the intake boot O-rings, Intake boots and airbox boots first.

[pw1382]

Yes, the shaft seals. I've replaced the intake o rings a few weeks back and the boots look good, no cracks and still soft. When I do the W-D40 "trick" it picks it up between cylinder 1 and 2. And since the boots and o rings where in good shape I thought it might be the shaft seals.
If they aren't o rings than how do I go about replacing them?

Thanks for the help,
Preston