Hitchcocks Forum

So everything is sweet with the 1 1/18th 389 fitted to my 350 thanks largely to The Bullet Whisperers invaluable advice. However even though it is perfect at high speeds, never fouls plugs and starts easily and always there is still an annoying flat spot between idle and take off once the motor is warm. This also results is the classic conking out at the lights unless you blip the throttle before engaging gear and powering off. There doesn't seem to be any spot on the idle screw to fix this and I'm wondering if the idle circuit jet is too big? It does seem to be an excessive richness issue as it doesn't spit and stop it just fades and fails, generally starting easily with a single kick. My plan is to take the current jet measure its hole size, solder it up and re drill .25mm smaller. I'd love to hear though if anyone else has solved a similar issue.

I think you are on the right track Simon pilot jet sometimes is so critical, other times doesn't matter

Ok so my numbers were a bit wayward. The jet stamped 30 had a .45mm hole so I soldered it up and drilled it out with a .4mm bit the smallest I have available. This does seem to have made a difference as the response off the throttle seems better but I've celebrated prematurely before so ill report again after a decent run.

Simon, I had exactly this symptom with a Monobloc on a Tiger Cub. It turned out to be float height. To find out if it is, just turn the fuel off while riding and see if the symptom disappears (before the carb runs dry obviously) Have a read here.http://www.whfolk.co.uk/REOCHUMBER/Arti ... nobloc.htm

I thought of the float height as the height it was set as was happenstance rather than anything intentional. I measured it using the the plastic tube over the idle jet held up against the side of the bowl cover. It came up to exactly the nipple in the middle of the bowl cover so its apparently dead right. I will try the fuel tap trick though. Cheers S.

Ok PeteF I took your advice and lowered the float level and it instantly leaned the idle circuit up without interestingly effecting the rest of the throttle range. I've drilled the idle jet back out to .45mm and will see if this has the desired result. I have to say it is fascinating tuning a carb ( much more fun on a single rather than a twin!) and incredibly subtile. The process has been slow having started with a worn out body and bushing it in brass then a new slide and the another with a different cut away and so on. I'm so close now and every time I make small improvements. Endlessly interesting but the next move is to get hold of an exhaust gas analyser and get really serious!

Interesting that lowering the float (even though you say it was correct) has this effect. Anyway, if it achieves the desired result........

Yes I have yet to check the level that its at now but before it was precisely at the nipple in the middle of e bowl cover. I will report on progress the day looks to be a goodun for motorcycles.