carburetion or advance issue?

[tommystinson]

If I could get an XSive opinion on this one:

My 79 SF alternates between what feels like slight engine power "ups and downs" while at speed under very light throttle, less than 1/4 or so. This is very subtle, but still noticeable. It's tightly synched, and colortuned pretty much spot on. I'll double check, but the spark is pretty strong. (accel coils, solid core wires, NOS pickups and NGK Iridium IX plugs at .040 along with a NOS centrifugal advance mechanism) I was thinking about checking the vacuum advance. It's not the drivetrain lash, I've gotten used to our clunky XS's. Perhaps a diaphragm? Thoughts/ideas?

[planedick]

Try this

Take off the left side cover and observe if the vac advance is moving up and down while you are experiencing the problem.

[pggg]

A subtle 'surging' under steady light throttle - sounds like a lean condition to me, (although possibly pinholes in a slide diaphragm) Raising the slide needles one notch or alternatively going up a size on the pilot and/or mainjet can smooth the fuel delivery if that's the case, but check the vac-timing operation anyway..

PS .. TC's gonna roll his eyes at this one - but Tom, you're NOT running inline filters by any chance?

[79XS11F]

When you color tuned it did you go for the "perfect" blue flame? I read this where I bought mine. It is part of the how to use color tune that was posted by the seller.

On the Yamaha XS1100s folks have discovered that cobalt blue settings don't run well on this bike. The engine on this machine likes a bit more fuel (a little richer). So tuners here go for just the emergence of a yellow //flame. Achieve this setting by turning the idle mixture screw. Left is richer / right is leaner (on every carburetor I've ever worked on!).

Rob

[petejw]

Could also be ur float levels

check this link out
its been on here b4
and is a good read


http://www.factorypro.com/tech_tunin...m_engines.html