Stumped!!

[hartleygs]

I have a 1981 GS850GL. When it is cold and you start it with the choke on it pops out the exhaust until it warms up then its fine. It revs good in the garage and seems like it would work great until you drive it!! When you are in 5th gear and try to accelerate it just bogs and will not move. It seems like anything at 5000 rpm or more is crappy. I cleaned the carbs twice. They are spotless. Tried different coils, inspected the intakes for cracks and air leaks. The clamps for the intakes are not tight at all. They bottom out before getting as tight as I like to see them. When you crank the engine how much fuel should pump out of the tank? It just seems like there is a fuel problem at higher rpms. When it starts to stumble at 5000 if I pull out the choke it revs fine. Could there be a lean condition? Please any help would be awesome!!!!! Shawn, PS, Bike has 23000 miles

[8trackmind]

Sounds like an intake leak between the carbs and the airbox. The two center boots are hard to seat. Are you sure you don't have a leak there?

[bonanzadave]

Completly tear down and rebuild your engine and buy a new set of carbs.

Just kidding.

Id check the petcock and the vac and fuel lines on it. How does it run on pri ?

Welcome !!

[hartleygs]

It seems to be a little better on prime. There just doesnt seem to be much fuel pumping out of the tank and everything seems to be clear of obstructions. I put a temp gun on the pipes and the two center ones run at 170 to 205 and numbers 1 and 4 are at about 270. I can usually figure this stuff out but im lost on this one.

[bonanzadave]

When you get low on fuel Id pull that petcock and check & clean the screen.

[speedzter2000]

Take the petcock apart. Mine had 4 screws. I took it apart, and found the diaphragm had shrunk. Get OEM from bikebandit if you must replace it.
Good luck!:-D

[nabrams]

What about the two often-ignored yet critical verifications:
1. Compression
2. Valve clearance

Low compression (most often due to insufficient valve clearance) would certainly be a suspect for the symptoms you describe. Most bikes have never had the valve clearances adjusted. The bike will run fine for about 20K miles until the problem surfaces.

[craze1cars]

The clamps for the intakes are not tight at all... They bottom out before getting as tight as I like to see them....When it starts to stumble at 5000 if I pull out the choke it revs fine...Could there be a lean condition?

Here's my thoughts: I'm far from an expert here, but your above comments hit me straight away, and 8trackmind has already suggested what I think your problem most likely is, though I'd more likely suspect the leak is probably at your intake boots rather than between carbs and airbox where he suggested... At higher RPMs air volume being pumped through the engine is greatly increased. This will tend to draw some air from around your poorly clamped intake boots, even if they don't leak at lower garage-tuning/leak testing speeds. And when this happens, it will create a lean condition at high RPMS. And then when you pull the choke, this temporarily enrichens the mixture by forcing it to pull more fuel to feed the excess air that the carbs didn't know about, and this lets it rev fine.

So based on all of your above comments, I agree this sounds like a classic intake air leak to me. And cheap and easy for you to correct with some new clamps, which you seem to need anyway, so nothing lost if I'm wrong. And obviously as 8track suggests, make sure all the boots are FULLY seated. And I found this was a true PITA on my bike when I reinstalled my carbs...it takes some real muscle and finesse.

I'd fix that problem first, not enough fuel delivery is IMO a less likely problem, but possible nonetheless. These bikes don't need to pump much fuel to run properly, that's why they get such good fuel mileage...

Good luck!

[8trackmind]

If he has a intake leak at the engine to carb boots, (or manifold o rings) it would idle very high as soon as it warms up. The classic CV carb "falls on it's face" at the same rpm every time is caused by the slides being not being pulled all the way up because there is too much air on the airbox side. The carb is reacting to what it thinks is part throttle condition. (This is why people have so much trouble tuning them with pods)

[Dave8338]

Ditto.......intake side of carbs.

[hartleygs]

awesome response guys

You have all been a huge help to me and I appreciate every idea greatly. Im heading to the garage right now. Ill let you all know in a while. Thanks again. Shawn

[bwringer]

Double dittos on checking the valve clearances... this gets neglected to a sad degree and will make the bike run like a moped.

The manual calls for a valve check every 4,000 miles.