83 GS850G hesitation off idle, stumbling at cruise

[bwringer]

Hello --

I ride a 1983 GS850GD, and I've been noticing lately that there's a slight hesitation when I roll back on the throttle after coasting. For example, rolling back into the throttle after entering a corner is a little ragged. Not much, but it is not the perfect throttle response I'm used to.

Opening the throttle at a stop, like at a light, is fine -- the problem only seems to happen at speed. Maybe it has something to do with using engine braking.

I'm also feeling a slight stumble when I'm cruising along at 50 - 60 mph, when the throttle is just barely open.

Maybe high engine vacuum situations have something to do with it.

The carbs are synched (just checked last night, and they were spot-on), the plugs look perfect, the intake boots are in great shape and the intake o-rings are new. The carbs are wearing fresh o-rings (rebuilt last summer) and are spotless inside. The boots between the air box and carbs are in great shape. The bike starts instantly at any temperature, idles perfectly, and otherwise runs great.

My only theory so far is a bad float or needle seat. I'm going to work on a method of measuring actual fuel level with a hose attached to the bowl drain, and maybe remove and weigh the floats.

So help me think through this, O great GS collective mind. It's a slight carburetion problem that some people would never notice, but it's driving me nuts. I'm just strange that way.

Any ideas?

[dgeorge]

Brian, have you checked your air filter recently? It could be that it is getting dirty and not allowing enough air flow in those situations.

[bwringer]

Hmm... good idea...

I haven't checked or cleaned my air filter since last year, although the oiled foam (which is the stock air filter on a GS850) is pretty resistant to clogging, and I certainly haven't been mud bogging. The foam element is only two or three years old, so it shouldn't be crumbling yet.

Hmmmm... and if the problem is fairly subtle, it wouldn't necessarily show up on the plugs.

I'll check that tonight.

[dgeorge]

I've got the same type of filter and I think the manuel says to clean it and reoil it at least once a year.

[bwringer]

SOLVED! (Boy, do I feel like an idiot...)

Wow, do I feel like a schmoe.

I pulled my air filter, cleaned and re-oiled the foam element and now the bike is running perfectly!

Thanks for the suggestion!

That's the last time I assume a foam air filter is OK just because there aren't any visible bird nests on it.

he filter looked pretty good from the outside, but it took a couple of changes of the water and dish soap to get the job done. I let it dry out for a day, lightly coated it with engine oil, squeezed out the excess oil, replaced, and my bike is back to its old self again. Woohoo!