Fresh BBK Stubling and misfiring By scootcanic (Read 347 times)

[scootcanic]

Here's the details. We just installed "100cc" BBK. Performance cam, big valve head, new blue style CDI, fresh ignition coil (orange if it matters), 95 jet. Stock intake, carb and exhaust. It idles wonderfully can not complain about that. I have followed Alleyoop's carb tune procedure to a tee. All jets are clean ports are clean, idle speed changes with mixture screw when adjusted. All is good until we drive it.

When we take it for a spin, it stumbles on acceleration. I have tried richer and leaner, does it less when lean on acceleration but then the second portion kicks in, when on the throttle constant it feels like a misfire here and there. If it is richer it doesn't do that as much but still noticeable. When lean it is very bad. I cant find the happy medium unless there is something I am missing all together?

[minesweeper]

This is going to sound completely off the wall, but I had the same thing happen and it turned out to be the coil. It was a combination of erratic spark and mildly aberrant fuel delivery. If you have another coil around just swap it out and see if it makes a difference, if not...well then now we know.

[alleyoop]

Have you tried raising the needle to feed it more fuel in the midrange and a little more on the top end since you say if you lean it out it is worse means you need a little more fuel in the mid-range and top end so you may need to get a little bigger main jet.
Alleyoop

[scootcanic]

Ended up needing a different jet all together. It runs like a top with a 90 jet installed.

[alleyoop]

Fantastic!! Good job
Ride safe
Alleyoop