correct jetting and needle setting

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surftalks
ICOA Member
ICOA Member
Posts: 95
Joined: Fri Jan 07, 2005 6:38 pm
Location: Dublin, Ohio

correct jetting and needle setting

Post by surftalks »

I'm getting ready to install the carbs back on the engine (engine is in tilt position now). I would like to jet them properly (or close) before installing them.

Here's my setup:

1979 CBX with stock Keihin carbs (98 main and 65 primary) air mixture screw 2.5 turns, floats at stock setting with Honda float guage.
Engine freshly overhauled, full valve job, appox 2 hours breakin on stand with stock carbs (starts and runs but now perfect) hesitation off idle (without a slight choke), a little flat from 3k to 6k, high end not tested.
Leakdown test shows 79-80/80 all cylinders.

Altitude 1000' msl
Wiseco high compression pistions (10.25:1 67.5mm) 1147cc
Stock HM422 exhaust
Stock Cams (intake and exhaust all set between 0.06mm and 0.08mm)
Stock airbox with K&N filter

I've contacted Dynajet and Sigma and both have totally different solutions: All give the same info as above.
Dynajet stage 1 recommends: main jet changed to 96 primary leave at 65 (no change) and needles on 4th groove from the top.
Dynajet stage 3 recommends: main jet changed to 100 primary to 74 and needles 1st groove from top.
Oldschoolcarbs recommends: Main jet changed to 110 primary to 72 or 74, leave needles alone, open mixure to 3 turns
Sigmajet recommends: main jet changed to 117.5 primary to 80 and raising the stock needle with two shims under.

As you can see, the recommendations are all over the place.
Does anyone here have a similar setup as mine and can recommend what works in the "real world"?

Any advice would be helpful.

Thanks,
C.
Craig
Dublin, Ohio

ICOA 5921
AMA
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Pilot ASEL Instrument

1979 Honda CBX Candy Glory Red
1979 Honda CBX Perseus Silver
1979 Honda CBX Black
1983 Honda CB1100F Faster Red (SOLD)
RANS Venterra S-19 N519CS

daves79x
ICOA Technical Director
ICOA Technical Director
Posts: 4738
Joined: Sun Oct 01, 2006 8:05 am
Location: Knox, PA
Location: Knox, PA

Re: correct jetting and needle setting

Post by daves79x »

Here's my .02: 70 primary main, 100 secondary main, pilot at 2 turns, no needle shimming. Use only genuine Keihin jets - you can get them at PJ Motorsports in Oregon or lots of other places. Just make sure they are Keihin and not Dynajet. Get rid of the K&N and go to the stock oiled foam or pleated paper. Do NOT use any of the Stage 1 or Stage 3 stuff. The bike will run just fine set this way and still get decent mileage.

Dave

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