My 400F had similar trouble - I never have had it on a dyno/analyzer to tell what's really happening but the plug checks all look good now. I reshaped the needles myself, not very scientifically but it worked. WFO was fine, midrange lean, and low throttle was just on the rich side. I couldn't change the partial by any means I could devise. To richen up the midrange, I marked a needle while holding the throttle at the right spot. Removed all needles and chucked each in a hand drill, then held a cloth with Brasso on it and squeezed the needle where I wanted more gas. By using what I considered equal pressure and equal time on each needle to make them the same, after a few tries I had reasonable looking plugs at all throttle settings and no more stumbling/missing. This was for a mod involving a Yosh 466 kit, cam, exhaust, and pods.
> -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of > [EMAIL PROTECTED] > Sent: 04.03.15 16:08 > To: Multiple recipients of list > Subject: Re: 750/4 Needle Profiles? > > > >Phill, > > > Why won't dropping the needles help your situation? Have you changed > >the displacement? And/ or the exhaust back pressure? Are your existing > >needles worn? > > Dropping the needles leans off the partial opening, but does the same for > everything greater as well. The engine goes *very* lean at wider throttle > openings when the needles are at their lowest, but still not quite lean > enough at a crack off closed. I have tried virtually every combination of > 3 different slide sets, needles (including a brand new set from Canada), > and emulsion tubes. > > It's an 836 with Yoshimura cam and a Transac 4->1 exhaust. All this work > (except the Transac) was done before I bought the bike. > > > Regards, > Phill >
