I got my B40F started recently. I started the tuning process. (Haven't done the stage 1 main jet test as I'm not MOT'd so garage bound currently). Did stage two to set the idle speed. It was idling a little bit erratically,but could leave it idling pretty happily.
I come back a week later & it still starts easily, but is erratic and won't idle. I haven't changed the pilot jet,throttle stop or cable adjuster. I can keep it running ( & ensure it's warmed up) by holding the throttle open a bit, but it's erratic. Interestingly if I carefully keep the throttle in one place at 1/8 or below.....the revs are wavering up and down. (It's also erratic above 1/8 )
Advice on possible causes welcome
My guesses so far are:
a) air leak at carb ( or possibly at exhaust) possible I guess that the carb is trying to shake itself loose at the flanges...but nothing lobvious to the eye. Anyway to check for small leaks ?
b) worn throttle slide: it doesn't look very worn and seems a snug fit.
b) ethanol/gummimg up of carb problem with old float, float needle and fuel hose. However I've put Millers VSPE Power Plus in the fuel...so was hoping that would avoid this possible problem.
(I'll look for crud/gum next week as I'll be replacing my existing not very worn 3.5 slide with the correct cut-out 3 slide....but the slide cut-out should affect the idle as far as I can see)
c) dirt/rust in the fuel : shouldn't be as I have just lined the tank with POR -15
d) spark: don't see why this would have changed as haven't tinkered with points since then and not sure it would cause erratic idle
yours a bit confused
HoogerBooger
If nothing has been messed with it's probably a bit of dirt in the carb.
A lined tank doesn't mean no contaminated or dirty petrol will go into the carb.
The carb is easy to set up - the bikes are not too fussy with settings.
If the jets, slide, float level is at the original spec there shouldn't be much
Of a problem with getting the engine to run satisfactorily.
However lots of things can cause an erratic idle!
You could do with giving the bike a bit of a run and then setting the carb up.
I can check for dirt in carb when I strip it again next week. Not that likely to be the cause though, as everything in the fuel system has been cleaned & I put the fuel in...from a clear container........mind you I haven't been to spec savers recently so I guess something could have sneaked through.
Carb is not as originally set up...but I highlight that it idled pretty ok last week. I shall leave dirt in fuel on my check list.
can't take it on a run without MOT or insurance ! what would it achieve ? apart from allowing the chop test on main jet size ?
An inline fuel filter, one of those cheap clear ones, will stop any crud and also allow you to see if any is present and getting stopped by the filter.
Setting up the carb after a run means that you have adjusted it when the engine is warm and not cold. I don't know my way around a B40 but if it has manual advance/retard, set that a bit retarded as well when you are adjusting the tickover/pilot mix
Hope you solve the problem soon!
Cheers
Pete