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Message started by metri on 10/05/07 at 21:25:51

Title: Carb tuning advice
Post by metri on 10/05/07 at 21:25:51

I got a new Mikuni VM roundslide carb and have it jetted right I think. Now by jetted correctly I mean not running rich, and not lean. This to my untrained mind means correctly. I played with pilot jets until it was rich and backed it off one etc. So the symptom:

When idling if I crack the throttle open full (or mostly) the thing just dies (if I hold it, but if let it go it will catch back). So silence when opened quickly at idle. This doesn't happen when it's moving fast, just at idle or going very slowly.

Is this normal? I'm not saying this is a problem, but an curious if it's dirt in the carb (as my gas tank is rusty) or just the way things work.... Any thoughts would be much appreciated. Thanks

Title: Re: Carb tuning advice
Post by Reelthing on 10/05/07 at 21:47:38

you said new - as new carb or new to you and is a used carb?

have you looked over the VM carb tuning guide?

http://www.mikunioz.com/download/pdf_files/vmmanual.pdf

by the way - when you do this - pull the plug is it wet?
carb might be too big - can't maintain enough air velocity when you quickly pull it open at idle -

no accel pump on that one - but it has an important air jet for top end - but top end is not you problem - it's just a problem with sudden wot?

Title: Re: Carb tuning advice
Post by slavy on 10/05/07 at 22:29:53

Try to raise the needle a little.

Title: Re: Carb tuning advice
Post by klx650sm2002 on 10/06/07 at 05:08:04

As well as raising (richening) the needle you could try a richer tickover.

Clive W :D

Title: Re: Carb tuning advice
Post by metri on 10/06/07 at 09:45:55

New new, not new to me. As for the plug, I don't think it's wet, as it's not seeming to be too rich, but I'll bite the bullet and check that too.

Yes it's only cracking it wide open from idle or going slowly. If I open the throttle smoothly is rev's right up.

Thanks for the ideas, I'll definately try the needle. I have played with pilot and main jets as well as setting the air mixture. But wasn't sure if you can just pop the throttle wide open from nothing and have it work... Thanks again