Motorcycle Repair: carb jet for open air filters, honda models, thread pitch

Question
Hi Bill
I got a CB77 from 1963
engine is in a good condition  , compression is 175 both sides ,
At the moment I got the carb jet  42# and 135#

What size of the jet do I need to use for an open air filter ?
Thanks ..
Michael .

Answer
Michael,

I am working on a 1963 CB77 right at the moment.....

I would use at least a #140 main jet for your bike. If you modified the exhaust as well, it may have to go to a #145.  Early Honda models used JIS thread pitch jets, so are harder to source than the later ones in ISO pitch. Those have a ring around the outer diameter to differentiate them from the JIS jets.

Always use the highest octane gasoline you can find and make sure the ignition timing spark advance does not go past the II marks on the rotor. This requires use of a dynamic/automotive timing light to verify.

Bill Silver
www.vintagehonda.com