Running problem. carbs? 100GS

[Windmill John]

Totally baffled now.
Bike was idling up to 3k
Stripped carb, looks good
Fitted new throttle cables, tappets done.
Here comes the strange bit.
After a run, the lowest I can get idle is 1500 to 1700 RPM
Throttle stops now don't even touch the cam and there is slack in throttle cables.
Choke cable adjusted.
Okay, it gets more weird.
Stick vaccumn gauges on.
Right hand carb doesn't do much, shows below 10 PSI even when I crack the throttle.
Left hand carb changes gauge with throttle; good.
Hang on , there's more.
Close the right hand mixture screw totally and revs drop; good.
Close the left hand mixture totally, nothing happens at all!!! It makes no difference.
What am I missing

John

 

[Kenny]

I'd seriously buy a carb service kit and start from scratch with new seals etc and give her a good clean whilst in bits. Easy to fit and sorts many problems out in one go.

 

[Valker]

Totally baffled now.
Bike was idling up to 3k
Stripped carb, looks good
Fitted new throttle cables, tappets done.
Here comes the strange bit.
After a run, the lowest I can get idle is 1500 to 1700 RPM
Throttle stops now don't even touch the cam and there is slack in throttle cables.
Choke cable adjusted.
Okay, it gets more weird.
Stick vaccumn gauges on.
Right hand carb doesn't do much, shows below 10 PSI even when I crack the throttle.
Left hand carb changes gauge with throttle; good.
Hang on , there's more.
Close the right hand mixture screw totally and revs drop; good.
Close the left hand mixture totally, nothing happens at all!!! It makes no difference.
What am I missing

John

I had a very similar problem on my 1993 GS PD "bing carbs"!!! I stripped out and cleaned the auxiliary chamber and lever , reset the cabs all is good.

 

[Steptoe]

Take out both mixture screws and compare lengths. Sometimes the fine end of one can break off and stick in place so no amount of turning will alter the idle speed.

 

[Windmill John]

Carb strip

Thanks guys, I'll strip em again

One of the mixture needles did look ever so slightly bent at the end; I'll get new ones.

Any ideas though why the lowest rpm is at least 1500 rpm, even with butterfly closed and throttle stops not touching?

Could that still be idle needle?
Also, why the rhs carb has no effect on the dial gauge?

John

 

[r100gser]

carbs

check float levels.

 

[John Armstrong]

check float levels.

I'm a bit new to airheads, but why would float levels high / low (might help if you said which) could make it idle fast

 

[BillN]

I'd seriously buy a carb service kit and start from scratch with new seals etc and give her a good clean whilst in bits. Easy to fit and sorts many problems out in one go.

You have probably got to the stage where there are now too many variables.........so Kenny's suggestion is the way to go

Buy the small Bing Book

Do one carb at a time - do not mix them up

Did you mention that you had checked the condition of the diaphragms and the seating thereof.....you may as well fit new ones while you are at it

Quick article this that you may as well read as it is written by someone who knows more than most of us lot

Good luck

 

[Windmill John]

Carb strip

As I bought the bike off a police bike mechanic and he'd fitted new diaphrams, I didn't check the carbs as thoroughly as normal.
I fully stripped my R80 carbs and rectified their problem.
I've just ordered new mixture needles, seals etc; guess what I'm doing on Saturday

 

[(RIP) pastyman]

could be that you have an air leak so i would also check the carb to head connection. a leak there could cause the revs to increase even though the butterfly is closed. only a thought

 

[SJRoome]

Hi

Check that the choke cables have clearance


Steve