Topic: Jets in 657 carburetor, where to start

[70CB750]

The 78F engine came to me with 657 carburetors jetted 40 and 100. The info I could find here and on Honda Chopper tells me I can keep the 40, but the #100 is too small.

What jet should I start with?  It is F2 engine with freshly rebuilt head and I will be using stock airbox and some half open exhaust 4-1 or 4-2.

I was thinking 105 or 110 for starts, what do you think?

[seanbarney41]

I have a very similar combo running 115's (40 pilots, assuming stock needle position but not sure, and also don't know the casting number but they are round tops, not pd's)right now (stock f3 motor, stock airbox w/ paper filter, old MAC 4 into 1 megaphone w/ straight through baffle)  It seems to run quite well but the weather has prevented me from riding it enough to know if changes need to be made.

[70CB750]

Thank you, Sean, that's exactly the info what I was looking for.  My engine has (per HM expertise) the cam 4.5 degrees advanced, but that should not make a difference in jetting.

I am not set on the exhaust yet, I have some old single pipes collected to 4-2 mufflers (old 70ties chopper style) I was thinking about using to build a custom 4-2 but I am afraid on the end of the build I will be tired of building a overrun by other projects and I will just throw a Mac at it and be done

As far as airbox, definitely stock.