rough idle, missing, and backfire

[legaleli]

I have a new issue: a rough and low idle, missing on initial acceleration, and an occasional backfire when idling after the bike is warm (and it's definitely backfire, or misfire, sounds like a deep "pop" and a ""whoosh" at the same time).

The missing on initial acceleration only happens when the bike is warm. Once the bike gets past 2nd gear there are no issuies with missing and the bike appears to be working properly. I pulled the airbox apart and resealed it, and I noticed some very old sponge seal the had degraded and there is a real possibility it ended up in the carb intake. The airbox is completely sealed now though.

I have noticed a slight bluing of the headers.

I pulled out the sparkplugs and there was black soot lining each ceramic stem but the electrodes on all the plugs were covered in a white dust.

Does this sound like a possible fuel issue or an airbox issue... or something different... the plugs and wires and coils are new.

Thanks again for any and all help!

[BassCliff]

Hi,

I'm looking into my crystal ball, getting a vague image of a motorcycle...but I can't tell what year or model.




Are your carbs in order? Properly cleaned? Properly jetted? Intake O-rings replaced? Vent tubes clear? Vacuum line clear? Fuel line clear? Petcock operating properly? Air filter properly cleaned and oiled? Properly sealed intake boots before and after the carbs? Float heights properly set?


Thank you for your indulgence,

BassCliff

[legaleli]

HA! I used that same pic for a post once a while ago on my facebook... good to see it again!

1982 GS850G - but I think you may have answered my question already - start with the carbs. As an aside I noticed that if I engage my choke slightly when the bike is warmed up the issue of the missing appears to go away.

I see work on my barbs in my future...

[BassCliff]

Hi Mr. legaleli,

Why not put your bike year/model in your signature file? Then you won't have to remember to type it in every time you ask a question. Sorry I didn't remember. I try to at least remember all of the 850 riders.


Thank you for your indulgence,

BassCliff

[legaleli]

Let this be a lesson to me...

I switched out the plugs - which were brand new, for new plugs. I did this because I read somewhere on this forum that a new bad plug was causing a misfire...

the result: my bike is now running without the backfire. It's amazing to me that a brand new B8ES can be faulty.

The NEXT thing I did was remove the airbox and pull the carbs off to find the source of a leak at the bowl of #1 carb.

the result: Two of the float bowl screws were not torqued at all. One of those two was actually stripped out completely and was rigged with a bolt on the other side (the bolt itself was shaped by a grinder to fit perfectly). Now #1 carb does not leak.

ALSO: The engine now seems to run more smoothly and there is no "popping" on deceleration. The disappearance of the popping surprised me because I thought that was the result of a leak in the exhaust - so maybe the two are not related... but nonetheless the airbox was NOT properly seated and is now properly seated.

My lesson: A thorough inspection of my "new to me" GS850G was required - even though I bought it from a dealer who claimed they went through the bike checking it over very well.

My next step will be to carbtune the carbs. There is a noticeable imbalance in the engine - especially noticeable in the low range - I'm hoping a balance will fix it. I will probably wait for winter to do the valves.

[Nessism]

The plug most likely fouled because the carbs are overly rich. If the float needles are not sealing correctly the fuel level will be high and cause the problem. Wouldn't hurt to wait til winter to attack the carbs but neglecting the valves makes me nervious since you could damage the valves. I suggest getting busy on that, it's a two step process anyway - measure the clearance and pull the shims to figure out what sizes you need, and then ordering the parts.

Good luck.

PS - aren't GS bikes great! It's always something.

[legaleli]

The plug most likely fouled because the carbs are overly rich. If the float needles are not sealing correctly the fuel level will be high and cause the problem. Wouldn't hurt to wait til winter to attack the carbs but neglecting the valves makes me nervious since you could damage the valves. I suggest getting busy on that, it's a two step process anyway - measure the clearance and pull the shims to figure out what sizes you need, and then ordering the parts.

Good luck.

PS - aren't GS bikes great! It's always something.

I LOVE my bike - wouldn't trade it for anything (except another GS!).

Interesting comment on the valves... given how everything else was put together I'm thinking I SHOULD have a look. The valves were recently adjusted by the shop from which I bought it (as in months ago with about 150Kms on the bike since). I'm wondering if the gasket seal that's on it now will hold if I try to reuse it...