sticking throttle

[Ozmadman]

My Model 8 runs fine and ticks over evenly and slowly when cold, the throttle slide snaps shut as soon as you close the throttle grip "UNTIL IT GETS HOT" then the tick over is all over the place ie fast/slow/stalling, you sometimes have to blip the throttle when you stop which seems to reset the idle speed otherwise it would cut out altogether or continually fiddle about with the idle screw, a few times I get a single spit back from the carb on tick over. When you close the throttle to change gear the revs don't decrease much as if the slide is sticking but when moving the bike runs and responds to the throttle well. The carb is in good nick with no appreciable wear, movement or scoring on the slide or carb body, all the needles and jets are new and the correct types, the needle is one notch down from central(weaker, but the exhaust is still black and sooty) and no air leaks that I can determine. I recently changed the throttle cable as I thought it was this but it still happens after about 10 minutes into a ride. Could it just be the crappy fuel (even though I have tried the more expensive stuff)these days and would a bit of UCL/oil in the petrol help what appears to be a sticking slide.. ANY IDEAS?

[Rob Harknett]

I assume you are opening the air slide, neadle not bent? no tight cable bends?

[Ozmadman]

I assume you are opening the air slide, neadle not bent? no tight cable bends?

Yep, all of those things are ok

[1608]

Symptomatic of loose main jet or auto A/R loose or malfunctioning. Check the timing. Its not the quality of fuel. The idle jet may be clear but is the corresponding idle drilling in the carb body clear also. Idle screw must be adjusted when engine is warm and on slow tick over.

[Ozmadman]

Symptomatic of loose main jet or auto A/R loose or malfunctioning. Check the timing. Its not the quality of fuel. The idle jet may be clear but is the corresponding idle drilling in the carb body clear also. Idle screw must be adjusted when engine is warm and on slow tick over.

Thanks, will check these out. The adv/rtd unit seems to work fine and expands and contracts freely with no real wear in the small pivots. I had this all apart recently and spent a lot of time meticulously setting the timing so now it starts first kick, no kickbacks and no rumbling in the exhaust. It does start without the choke ? Will check the main jet and pilot jet/drilling again just to be sure , why does it only happen when hot though?? And I mean't "continually fiddling" with the throttle stop screw and not the idle screw.

Paul

[iandusud]

Are you sure you've not got the mixture screw set too rich? Or maybe the float level too high. I wouldn't expect an engine to tickover slowly and steady when cold. As already said set the tickover with the engine up to temperature. Another thought is it might be badly worn slide which displays its symptoms more as the carb warms up and expands. Is it a concentric? These are very prone to wear. Have you checked to see what size pilot jet is fitted?

Good luck with sorting it out, Ian

[Rob Harknett]

Quite often something simple has been overlooked, recheck the carb and all its parts are the correct parts. That include the slide is correct, get the wrong cut away and you get all sorts of probs. re check neadle possition, float not sticking and the other suggestions made. I usualy have my air open all the time, probably cos I never use my bike when its really cold and may need a choke.

[Ozmadman]

Thanks guys

Will go over it again. The new needle/jets etc were all fine as I made sure they were the correct before I fitted them, will re-check the slide cutaway number, the float level(again, it was ok when I checked it a few months ago), the pilot screw adjustment and make sure there is no rubbish from the tank blocking anything, may just drop the needle one more notch to see if that cures it as it does appear to be a bit rich still... the choke slide btw is all the way up and invisible when looking down the venturi.

Paul

[rex.webb]

Sorry ?.
I am sure the Needle has no bearing on things when ticking over ?.

[1608]

May just be a simple case of flooding, hence running rich and easy to start without the choke. Check that float is cutting fuel off and no fibre wash under the float needle housing. Check correct needle and position.Carry out carb adjustments ie idle mixture screw and throttle stop screw ( lowered ). I exchanged my plastic float for a brass one as it kept sticking.