Dear All,
I don't remember whether I've already asked this question (sorry if so):
My 99 is now running very well whith her new Pazon ignition.
She is equipped with a new 28mm Amal concentric, 220 main jet /3,5 slide cutaway /106 needle jet and needle at 2nd groove /no air filter.
Sparkplugs (NGK BP7S) look OK (colour-wise).
The only remaining issue is at idle when hot: she stalls systematically. Sometimes, she sort of "spits back" through the carb at very low revs (as if there was toomuch timing advance, which is not the case. No kick-back, revs up well etc.)
I've been told that those symptoms show a weak carburation and may come from a too steep (3,5) slide-cutaway. Dale Middlehurst recommended me a 2,5 but I didn't paid enough attention when ordering the new carb. Sorry Dale...
Thanks for letting me know your thoughts about that. Do you think that an air-filter may help too(in addition to protecting the engine)?
Kind Regards,
Laurent
Laurent, an air cleaner is…
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Merci beaucoup John, I'll…
Merci beaucoup John,
I'll follow your advice soon re: the air filter. Your comments regarding the non impact of cutaway on my idle problem is shared by other friends.
The thing is that Concentrics(at least, those provided by Burlen) are no longer equipped with a pilot jet as they were in the past, so I have no other way toadjust the mixture at idle than using the air-screw, which I did and it proved non-effective.
I've never seen (yet) spits-back generating a flame but I'll have to find a solution soon (not very comfortable with the idea of a flame under the petrol tank of my dear Dommie). I guess that theair filter will be able to sort of "trap" the flame.
Regards,
L.
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Laurent, you have fitted a…
Laurent, you have fitted a new carb,and hopefully it hasnt worn out yet, but it might be wise to just check how loose the slide is in the body. Any air leak will cause your type of problem, and methods of testing for air leaks are well known so I wont repeat them.If you are of a mind to increase the pilot jet, a watchmakers reamer, sometimes termed a quarissor,will do the trick.I may be wrong , but I dont think the concentric ever had a removable pilot, the monoblock yes,the jet could be replaced. Regards John.
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Laurent, I must point out…
Laurent, I must point out that my knowlege of bike progress ceases at 1970,when I went over to the dark side, so concentric means pre 70.Regards John.
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Laurent, an air cleaner is allways a good idea, essential if you live in a dry area. You will need to reduce the mainjet by 10 or 20 in size to compensate.Cutaway doesnt affect idle , but off idle as you accelerate engine speed. Cutaway can be changed by filing the slide, .0625" removed from the lower edge will give you a 2.5, or buy a new slide.As you say a spit back is lean mixture,allways accompanied by a flame inside the manifold, in the dark seen as blue white color.Regards John.