Hesitation on GS1000E

[drewandkellie]

My 1980 GS1000E is completely stock has 9000 miles on it, has always been stored inside and is immaculate. The only problem I have is when it starts. It starts nicely and warms up fine, but when I take off and accelerate, it hesitates, actually more like breaks up, at around 2500 RPMs, If I ride over 3000 rpm its fine. under 2000 rpm is ok as well. It will do this for about 15 to 25 minutes of riding then it smooths out and runs perfect.
Any thoughts.

[tkent02]

Running better when fully warmed up sounds just a tiny bit lean, have you ever had the carburetors off for cleaning? Ever adjusted the mixture screws?

[drewandkellie]

The mixture screws are still capped off, never touched. Carbs were cleaned once several years ago but left stock. Just a though, I wonder if the 10% Ethanol gas we use here in NJ is enough to make it run a bit leaner?

[tkent02]

These bikes in the late seventies and early eighties were adjusted very lean from the factory, as lean as could be in the pilot circuits. This was to satisfy the EPA, not for power or even gas mileage. Even if everything on the bike was identical, with the gas today it would be a tiny bit too lean. Some models of GSes seem to be worse than others but all of them could use a tiny bit more fuel, raising the jet needles and adjusting the mixture screws a small amount will make a big difference. It will have much better throttle response, more power and get better gas mileage.

It also makes sense to ensure everything else is perfect, valve clearances, throttles synchronized, etc.

It can't hurt to clean the carbs again, if the screws are still capped off they were not removed for cleaning, the passages which connect to those screws need to be cleaned. While you are in there also check the float levels.

There are several O rings in the carbs that should be replaced as well.

[Rudeman]

These bikes in the late seventies and early eighties were adjusted very lean from the factory, as lean as could be in the pilot circuits. This was to satisfy the EPA, not for power or even gas mileage. Even if everything on the bike was identical, with the gas today it would be a tiny bit too lean. Some models of GSes seem to be worse than others but all of them could use a tiny bit more fuel, raising the jet needles and adjusting the mixture screws a small amount will make a big difference. It will have much better throttle response, more power and get better gas mileage.

It also makes sense to ensure everything else is perfect, valve clearances, throttles synchronized, etc.

It can't hurt to clean the carbs again, if the screws are still capped off they were not removed for cleaning, the passages which connect to those screws need to be cleaned. While you are in there also check the float levels.

There are several O rings in the carbs that should be replaced as well.

It might be a good idea to replace the carb boot O-ings as well.

[tkent02]

It might be a good idea to replace the carb boot O-ings as well.

Yep, and check for any leaks around the airbox too.

[Nessism]

The rubber O-rings get hard and brittle after 30 years of submersion in gasoline. I recommend doing a full carb rebuild and refresh all the O-rings with a kit from cycleorings.com, including the intake boot pipe O-rings as well. After the bike is back up and running, tweak the mixture screws to achieve the highest idle speed and vacuum sync the carbs. Needless to say, performing a valve adjustment is manditory as well unless it's been done within the last 4000 miles.

Good luck

[KEITH KRAUSE]

Sure is a small rpm range that you notice a problem. But I'll go with a pilot circuit that's not clean. Lots of very small orifices in the pilot circuit.
Since a motor "richens" a little once warmed up and yours has that temporary problem until then, I'd say it's fuel starved. It can no longer handle the combination of a cold motor and semi-clogged jetting, so it stumbles until it's warm. You most likely still have a problem once warm but you just don't notice it.
Don't play with the mixture screws. If they've never been touched and it ran fine before, then don't play with them. It's not their fault.
Such low mileage means the bike sits a lot and any fuel in the carbs will eventually layer the parts in a varnish. Enough varnishing and things get clogged up.