Topic: Re-Jetting Question - 1976 CB750F

[Blackfin5]

I did a search but could not find specifics.  In my "Blaster" build thread, I mentioned that the bike is running lean, hitting a flat spot around 7000-7500, and running hot (I believe anyway).

Stock set-up with 064a carbs; 105 mains; 40 pilots; and needle clip in 3rd position (middle).  Floats at 26mm.

For now, I'm running with 4-2-1 motogp exhaust and stock air box with new K&N filter.  Otherwise engine is OEM.

I ride mostly at 2000 - 3000 ft elevation.

My thinking is first switch to 110 mains; and then possibly to 42 pilots with same clip position.  No dyno is available.

Has anyone successfully re-jetted this same yr/model with after-market 4-2-1 exhaust who may lend a suggestion or 2?

Cheers!

[Don R]

I used 110's with stock pilots and can't remember where the needles ended up. I've checked floats with clear tube. It runs great but idles rich smelling. I'm suspicous of the advancer on mine. The popular opinion is they are lean from the factory.
 Mine has the stock 76 header with my homemade glasspack muffler.

[flybox1]

make one change at a time.  start with 110 mains and test ride.
if your plugs still show lean, go to 115/120
only after your plug color at WOT is correct, should you start messing with clip position (2/3 throttle)
when this is good, then check plugs at 1/4 throttle and adjust pilot jet size as needed......
then plug color at idle and A/F mixture screw setting.

[Blackfin5]

Sounds like the correct approach.

Thanks, guys!

[Jerry Rxman Griffin aka MuthaF'er]

I vote for the mains 110's first. The needle jet is probably a little richer than new anyway from wear. Once you get the mains squared away then go to the needles. Remember that the mains and the needles overlap below your flat spot.

[Blackfin5]

Thanks, Jerry.  Good reminder.