Mechanical advance on GS850GL

[ChopperCharles]

I'm having issues with my buddy's GS850GL. It's been sitting for a while, and I went through the carbs. They're spotless. The pilot passages are clear, carb cleaner squirted through the pilot screw makes its way out the slow jet orifice. I've use all new OEM jets, not the aftermarket stuff. I've done this before, the carbs are clean beyond all get out.

What happens is this: The bike revs freely in neutral. No stumble, no difficulty revving, it revs like a new bike. It starts easily on a little choke, no throttle necessary. The problem is under load, it bogs like its running out of fuel. I slip the clutch and it revs, but put a little load on it and it bogs. Once it hits about 3500 rpm and stays there a second or two, suddenly I have full power. So long as i keep the revs up I've got power, but if I let them drop then it does the bogging again for a couple seconds, and then clears up.

I'm wondering if the advancer mechanism may not be working properly, may be sticking closed, and then suddenly opening to full advance once there's enough centripetal force from higher rpms. But it's just a theory.

I don't have a manual for the bike yet, and i don't want to start tearing off covers left and right. whereabouts is the mechanical advance on the 850GL?

It rides like one or two slides are sticking down, and then suddenly popping back up when engine vacuum is high enough for long enough, but i've verified that the slides all move in unison by removing the airbox and revving it in neutral.

Charles.

[Nessism]

Hi Charles,

Just so you know... the bike won't run correctly with the stock jetting unless the stock airbox is fitted, sealed, and the stock exhaust is in place. Assuming all is stock, don't overlook an electrical issue like a plug cap that has extra resistance. You might want to pull off each cap, snip off a small piece of wire, and screw the caps back on.

Regarding the advance mechanism: you should be able to remove the ignition cover, grab the rotor with your hand and turn it. It should turn smoothly against the spring pressure and snap back when released.

Last thing I'll mention is the carb boot O-rings. I strongly suggest you replace these, along with all the carb O-rings, while you are tuning the bike. Clean carbs is one thing but 30 year old O-rings are sure to be hard and brittle. Cycleorings.com is the place to get replacements if you haven't found them yet while searching the forum for information.

Good luck

[koolaid_kid]

Just to be more specific, the ignition cover is the right front cover as you are sitting on the bike. It is easily removed to check the advance mechanism.

[Steve]

The pilot passages are clear, carb cleaner squirted through the pilot screw makes its way out the slow jet orifice.

Not quite sure where you are squirting, as there is no "pilot screw", but I'm going to assume, for the time being, that you are removing the "idle mixture adjustment screw" and squirting in there. Yes, it's a straight shot down to the orifice that feeds the cylinder, but what about the other end of the same passage? If it is not able to draw fuel from the bowl, you will experience the exact symptoms you are describing. When you "went through the carbs", did you strip them and dip them? That's the best way to assure that all the passages inside the carb body are clear. Re-assembly with new o-rings from cycleorings.com is also highly recommended.

Is this where you were spraying?


.

[tom203]

I'm having issues with my buddy's GS850GL. It's been sitting for a while, and I went through the carbs. They're spotless. The pilot passages are clear, carb cleaner squirted through the pilot screw makes its way out the slow jet orifice.

Steve; I think he meant he removed pilot jet and blew it out to the idle/air mixture screw to ensure an open passage to carb throat.
ChopperCharles; since you disturbed the carb o-rings by removing carbs, they need to be replaced,cuz as others have said, this is a good place for an intake air leak.

[ChopperCharles]

No, guys I'm not new at this I ensured that carb cleaner sprayed in the idle air mixture screw orifice (called a pilot screw for Hondas) exited through the SLOW JET HOLDER inside the carburetor. I put my finger over the hole in the carb throat and made sure carb cleaner traveled through all the tiny passages, and exited where it was supposed to. I had these carbs completely stripped, every part removed, every passage cleaned, every o-ring replaced, and then I reassembled them all. I've done this many times before, just never to a 'Zook.

All of my test riding has been with the airbox and air filter in place.

Plugs are new, it did this with the old plugs as well. I'll replace the resistors in the caps with brass rod for good measure, but I doubt that's the problem.

I've sprayed ether around the carb boots, engine rpm does not change, so there are no leaks. Idle is rock solid stable, and it doesn't hang up at high rpm at all - it returns to idle quickly after revving, like it's supposed to.

Hope that paints a clearer picture.

Charles.

[Steve]

Yes, a better picture, for sure. Thanks.

We just see to many "new" guys spritz around some carb cleaner spray and call that a "carb cleaning", so we have to ask to be sure. Don't be offended.

.

[Graham]

I'm having issues with my buddy's GS850GL. It's been sitting for a while, and I went through the carbs. They're spotless. The pilot passages are clear, carb cleaner squirted through the pilot screw makes its way out the slow jet orifice. I've use all new OEM jets, not the aftermarket stuff. I've done this before, the carbs are clean beyond all get out.

What happens is this: The bike revs freely in neutral. No stumble, no difficulty revving, it revs like a new bike. It starts easily on a little choke, no throttle necessary. The problem is under load, it bogs like its running out of fuel. I slip the clutch and it revs, but put a little load on it and it bogs. Once it hits about 3500 rpm and stays there a second or two, suddenly I have full power. So long as i keep the revs up I've got power, but if I let them drop then it does the bogging again for a couple seconds, and then clears up.

I'm wondering if the advancer mechanism may not be working properly, may be sticking closed, and then suddenly opening to full advance once there's enough centripetal force from higher rpms. But it's just a theory.

I don't have a manual for the bike yet, and i don't want to start tearing off covers left and right. whereabouts is the mechanical advance on the 850GL?

It rides like one or two slides are sticking down, and then suddenly popping back up when engine vacuum is high enough for long enough, but i've verified that the slides all move in unison by removing the airbox and revving it in neutral.

Charles.

Sounds like the mechanical advance. 81 and before 850gl had them on the right side of the crankshaft. 82 and after had electronic advance. Check BassCliff’s web site for a free manual.
http://members.dslextreme.com/users/bikecliff/
Not everyone here knows a “pilot screw” is an “idle fuel mixture screw” and I too check my carburetor circuits with carb cleaner even after a dip.

[ChopperCharles]

Well, the mechanical advance looks good, so it's not that. Going to try the plug caps next. If that doesn't fix it, I'll put a set of vacuum gauges on the motor and see if I can figure out what's going on.

Charles.

[tom203]

No, guys I'm not new at this I ensured that carb cleaner sprayed in the idle air mixture screw orifice (called a pilot screw for Hondas) exited through the SLOW JET HOLDER inside the carburetor. I put my finger over the hole in the carb throat and made sure carb cleaner traveled through all the tiny passages, and exited where it was supposed to. I had these carbs completely stripped, every part removed, every passage cleaned, every o-ring replaced, and then I reassembled them all. I've done this many times before,

Hope that paints a clearer picture.

Charles.

OK, I figured you had done this, and "every o-ring replaced"; but did you replace the large o-rings between the carb boot flanges and the cylinder head? While usually if these leak you have idle problems, who knows in your case! Thirty years of sitting won't leave them resilent.
Visit cycleorings.com. These carbs are very sensitive!

[ChopperCharles]

as i said, I squirted ether (starting fluid) all around the boots, and the idle didn't change, so they're not leaking.

Charles.

[tom203]

as i said, I squirted ether (starting fluid) all around the boots, and the idle didn't change, so they're not leaking.

Charles.

Well, you seem convinced about no intake leaks, so how about using a timing light to make sure advance mechanism is reasonably smooth from idle to 3000 rpm?

[ChopperCharles]

So after ruling out electrical and air leaks, I went in there and popped some 140 mains in instead of the 114. The bike was then ridable. there was still a lean spot there, but I could now accelerate through it and take the bike for an actual ride. About 5 minutes into the ride, all of a sudden the lean spot disappeared. I put the stock 115 mains back in, and the bike runs perfect now. I guess the carbs just needed some gas run through them after the rebuild. Bike runs great, now I just need to fix the gauges and a few other odds and ends.

Charles.