Mikuni VM - jetting guideline after boring out.

[sled-der]

I have a 340 TX and the 32 mm VMs were sad so I slipped on a pair of 34s. As this would be almost the same as boring a 32 rebored to 34 - I have to ask.

When you bore out a carb, lets say from 32 to 34, or 34 to 35.5 what is a good jetting guideline. More air means you'll need more fuel, would you increase the needle jet, raise the needle, increase main jet size - by how much to start with?

 

[mcshane48]

Start with a 280 main and go lean from there.

[Hoozier]

I went from 36 to 38mm on my Gpx and really didnt see a big difference. ran the same cutaway, needle jet and jet needle. main jet about the same also. its always a good idea go go a little fat andwork your way down

[sled-der]

Thanks, I would have thought it would make more of a difference.

I'll go up one for the needle jet, raise the needle 1 notch and increase the main a bit and see what happens.