lurching at slow speeds...

[mavis cruet]

righty ho. just got my '93 r100 gs back on the road after a lengthy refit (2 years goes by remarkably quickly these days!) to find her a very jerky ride at small throttle openings / slow speeds (30ish mph.). when stationary and you slowly increase the revs, between about 2500/3500 rpm there is a subtle 'bopping' from the exhaust note which seems to be caused by the left hand carb. (i incresed the revs to just below the bopping then pulled the throttle cable by hand on each side individually and the left produced the bopping.) the plugs are a fair bit blacker on this side too. im wondering if the left carb is running rich at these revs? i have cleaned both carbs and replaced the 'easy' o rings (including the choke assembly) but was going to give the left hand one another real good scrub and wondered which bits to concentrate on... apart from this the bike runs well and ticks over fine. im thinking it is not ignitiion as it is twin plugged and each coil runs a plug on each side. any thoughts??
cheers as always....

 

[DrFarkoff]

Check your idle mixture o ring and setting and check the needle is not badly worn at the circlip groove

I also had one where the choke gasket was shrunken and allowing air to be drawn through

 

[PW Cymru]

Check the choke cable is not too tight and the choke lever on the carb is seating closed properly.

Had a similar issue on my PD.

 

[DrFarkoff]

Good Call on that one!

I forgot about sticking chokes

And as usual with Airheads its usually a simple fix for a simple problem

Just pull on your choke lever and then push it off and see if your two chokes return to their stops pushing them off when you have started is a good interim solution (P.S. you did put the disc back on the right way around didn't you?)

 

[Kenny]

Choke does seem the suspect. If the choke returns OK...screw in the mixture control screw underneath that carb a half turn and see if that makes any immediate difference. If it does then back it out a quarter of a turn and see if running any better etc. Obviously make a note of how many turns from fully in the screw is at present ( either way it should not be exceeding 1.5 turns from fully turned in ). Worth a try

 

[mavis cruet]

replaced all the choke gaskets and deffo not swapped the discs (always 1 carb apart at a time!). not sure about the choke cable. never really used the choke in 100,000 miles. always start on a bit of throttle and keep it open a tad till it warms up. never liked running on choke. will check the needle clips and groove wear. will keep you informed...

 

[Padmei]

Hey mavis not sure if you've already checked - you prob have- but my bike had been running like a pig below 3K revs then come alive with a lurch above that.
After running thru all the possible problems in my head on my ride this morning I stopped & checked the throttle cables. They had crept out of adjustment. I tightened them up to the point of increasing the idle then backed them both off a tad.
The bike just sang after that. I'll need to synch them but made a big difference from what they were.
cheers