GS850G Cuts out when cold

[bwringer]

Whenever it's below about 60 degrees, my '83 GS850G cuts out at higher RPM under load.

The bike starts, idles, and runs perfectly in the driveway, but once on the road, it won't pull above 2,000 - 3,000 rpm -- it cuts out like it's not getting any gas. It idles normally, and will rev at a stoplight, but won't pull. The choke works normally.

This behavior slowly goes away as the engine warms up. After about ten minutes, the bike runs perfectly. If it's warm outside, the problem doesn't happen. FWIW, I got caught in a downpour on the highway a couple of days ago, and the bike ran perfectly the whole time.

The spark plugs look fine, and the Dyna coils and plug wires also seem OK. I've done a quick check of the wiring connections under the tank. Everything looked fine, but I didn't have time to bring out the voltmeter.

Since it's related so closely to temperature, I'm thinking I might need to more closely investigate the whole ignition sytem wiring and grounding.

I'm also thinking that one or more of the CV sliders in the carbs might be sticky, or at least a little gummy when it's cold and intake vacuum is high. Probably a long shot, but worth checking. The bike has been running perfectly for a while, so it's gone about 15K miles without pulling the carbs off.

The charging system and battery check out fine, and there aren't any other electrical problems.

I checked valve clearances and carb sync about a month ago, and everything was spot-on.

Any other ideas?

[robinjo]

Sounds like a carb problem to me, is it running lean?

[argonsagas]

Check the choke connections at each carb. Each one has a screw lock to keep it in position against the choke rail.

If you have a screw loose.......Welcome to the Forum!



You may have a loose one, (or two) that allows the rail to move a bit without having the needed effect on the carb(s). That would cause the complaint you have, as the engine would be labouring along only on the cylinders that had the full gas feed, and the complaint would disappear when the engine warmed up, and you turned off the choke.

[KEITH KRAUSE]

Sounds like it's running lean, which would be more noticable when it's colder. First make sure your carb boots and manifold clamps are tight.
If they are good, I would check/clean the pilot jets and the pilot circuits.

[saaz]

The behavior sounds like a typical well tuned standard bike that still meets emissions...congratulations! They were tuned on the lean side standard, which makes them very cold blooded. With age it may get worse, as suggested above. A little clean and perhaps retune might make it better from a rideability point of view.

[bwringer]

Hmmmm...

The choke is working normally, and all the choke and throttle linkages are working fine.

The high today in Indiana was about 78F, so I rode to work (about 130 miles total), and the bike ran perfectly both ways. It was about 63 when I left the driveway.

According to the plugs, the bike is not running lean. Perfect tan/grey.

Looks like I'll need to verify the problem still exists in a few days when temps return to normal (about 50F). Assuming it's still there, it looks like the carbs need to come out for the old inspect/clean routine. I have a set of the carb O-rings that one guy was selling a few months ago, so I should be OK there.

The bike didn't always run great, so I definitely know how to get the carbs out and back in fast!

Thanks everyone! I'll let you know in a few days...