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Motorcycle Repair/carb jet for open air filters


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 .


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

Motorcycle Repair

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Bill Silver


Need help with vintage Hondas from the 1960s? I am an expert with 250-305cc bikes in particular and most all of the other pre-91 models, in general. I do NOT claim to have a great deal of experience on Gold Wings, Cruisers, ATC/ATVs and dirt bikes.


I have owned/ridden/maintained Honda motorcycles for 35 years. I have written five books on Honda repairs and collecting. I was a service manager for two Honda shops back in the 1980s.

VJMC (Vintage Japanese Motorcycle Club) of North America

VJMC newsletter, as editor for two years and as contributing editor currently.

3 years auto shop in high school, teacher's aide in Automotive Technology in Jr. College, Diesel mechanic course in college, self-taught mechanic and automotive writer.

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