Taffy

i thought i'd start this post to help all you numpties that can't get a handle on starting your bikes.

most of you won't have sat and thought about this before but after you have read this i hope you'll get your shoot together and put some BRAIN POWER into it!!!

having modified carbs for years i have found that every change at the lower end of the jetting has created a problem or change elsewhere.

the dell orto carb has a choke jet that can get bunged up-especially if the carb and steed haven't been used for a couple of months. it will need cleaning out and should be held up to the light. the hole should be quite large and the trouble is that after cleaniung it may be no better. at least .5mm wide is how it should look.

the jet sizes on the keihin are actually basically only a metric drill size so a 180MJ is 1.8mm. that doesn't though make it smart to go round drilling jets!

the important thing is to LISTEN TO THE ENGINE. this is something that few people do. they bitch coz it doesn't start yet the engine is trying to tell them something!

the reason we have fun with carbs is because it's the LAST thing we fettle. everything else is set and the carb REACTS TO THE ENGINE. and that is the fascination and why it is so hard to help people.

this is what i look for when i start a bike;

lean on choke
the bike is a bitch to start and takes 30 kicks. each time it starts it runs a little longer until after 5 minutes it runs fine. it probably now doesn't like any throttle!

slightly lean on choke
the bike starts and judders for anything up to 10 seconds before it build up revs and builds up revs then revs like an idiot compared to starting! this bike will never 8-stroke and you can go to the loo/tog up ready, lock the garage - the lot-it ain't gonna stall!

spot-on
bike runs at medium high revs for at least 30-40 seconds before starting to 8-stroke mildly. it should run straight away at high revs and not build up. the revs should stay the same for over a minute before perhaps 8-stroking mildly and losing revs-it shouldn't stall. it shouldn't 8-stroke any sooner.

slightly rich on choke
bike starts well everytime but you need to blip the throttle or the revs might drop and it might stall. you have to be near the machine! 8-strokes within 10 seconds.

rich on choke
bike starts fine but within 1, 2 or 3 seconds it 8-strokes.

on the keihin carb even the MJ affects starting-seriously! so every mod you make has a knock on effect.

different choke jets are available from yamaha but you can't get them from keihin themselves for some reason (well it used to be like that!) so yamaha are the boys!

i have several choke jets and i used to always be swopping them out. everytime you change the needle straight (very last suffix letter) you will effect the starting. the PJ is only a small part compared to the needle straight. i have estimated it to be 80%/20% needle straight to PJ effect on starting with the FCR.

with the dell ortos the starting is really just the effect of the choke jet combined with the slide cutaway and PJ. that's why it's a lot harder to understand but not necassarily a problem in itself.

so next time listen to your engine!!!!

regards

Taffy

BendBerg

I am in awe just when I thought my carb was tunned, a guy on a whole other continent has to tell me my choke is lean! And he never even heard my bike run, amazing! Taffy, I am not being sarcastic, by your description I have a lean choke circuit, and just when I thought that thing was tunned. Thanks Taffy.

Taffy

i fitted a brand new choke jet which i had as a spare to the machine i borrowed from gary grover racing on 26th june. go see my race report. it was a 470 with a blocked choke jet.

just as i described above!!!

glad i'm able to help!

regards

Taffy