To re-jet or not to re-jet

[HCDawg]

I bought my 79 CBX in 1984 as a fixer upper, I repaired it back to original, rode it for a while then had the motor bored to 1149cc 30 years ago, I sold the bike for $2k after a season before getting the carb issues delt with, I sold it to a friend of mine when my son was born, my friend rode it for a season, then it sat for 29 yrs in a warehouse. I got sentimental one night and called him up...he still had the bike, bought it for $5k...about $100 a year for storage. Stock carb filters, aftermarket 6-2 pipes, ran good till the upper rpm’s and it was stalling...I’m old now so the mind wonders...I know I bumped up the jets and may have shimmed the needles. Lower rpm’s it’s fine....everything I read from the pro, s here say leave everything original. I’m starting restoration with the fuel system of course, tank is out getting the dent and rust out, red coated and original paint. Just bought Mike Nixon’s book on carb rebuilding and I’d like some insight into fixing the carb issues, he says leave the stock jetting and needle alone...I’m not sure...help?

[daves79x]

Lots of potential issues with a bike that's been sitting. The big-bore itself requires little if any jetting change, but there are many things to check. If you are keeping the stock filter, either paper or foam - NOT K&N - you should have the best luck with close-to-stock jetting. I would bump up the primary mains to 68 or 70 and leave the secondary mains at 98. The bike may not be opening up at higher rpms due to sticky slides, restricted intake or exhaust. When re-jetting, use only Keihin jets. If by chance you installed a Dyno-jet kit - get rid of it and go back to stock, although stock '79 needles are hard to find. You may be stuck using aftermarket needles there.

Then there are the other million things you need to do to re-commission a bike that's been sitting for that long. Good luck!

Dave

[Mike Nixon]

>Just bought Mike Nixon’s book on carb rebuilding and I’d like some insight into fixing the carb issues, he says leave the >stock jetting and needle alone...

Yup.

(Is it okay to + yourself...?)

As Dave has already pointed out, nothing is better than the stock carb parts. Also, though counterintuitive, a big bore, if done correctly, actually richens carburetion all by itself.