Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: mickwinf on July 23, 2026, 04:37:43 PM
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reading the other post about mixture screw setting i thought i would ask about a slight issue i have with Lazarus the 500 four. the carbs have been cleaned and rebuilt to standard spec, 100 main jats and 40 pilot. when i first got it on the road it was running very rich so adjusted pilpt screws until it ran better ( out is weaker BTW). thing is i have them turned out almost three full turns as thats when it runs best with no flat spots and pulls well. If I put 38 pilot jets would this bring adjustment back to normal range?
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Yes to that change in jet size and getting the effect you want.
Its a really clever little design that will show the way if working correctly.
Screw too far in (likely less than 3/4) shows its "calling" for a larger fuel jet. The opposite, as you experience, too many turns out needed to get it balanced in mixture will confirm the fuel jet has too much flow.
Winding the screw further out drops the vacuum (negative pressure) imparted on the fuel jet, to then pull less fuel up out of float bowl.
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Remind us please. Which carbs have you used and do you have a 4:1 exhaust fitted? 069A and 4:1 exhaust will definitely benefit from #38.
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All std including 4 into 4 pipes. 627b carbs
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All std including 4 into 4 pipes. 627b carbs
The CB500 always had bigger slow jets than the CB550: #40 vs #38. Even the CB500K3 with PD carbs had #42 where the CB550K3 had #38. Explanation anyone?
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The 069a carbs have bigger air bleeds, iirc the 627b has 5mm bleeds and the 069a has 7mm bleeds. An attempt by Honda to reduce emissions back in the 70s when California was getting very upset about smog.
The PD carbs are totally different in design so impossible really to compare like for like.