DCOE idle jets

[Guest Anonymous]

Someone a few days ago posted trying out 55F9 idle jets on their dcoe 40's to relieve that fuel-rich popping. I have the 45f9's, and have the same problem. I have a set of 50F8s, but what does the 50 mean, and the F8 or F9 mean again? More air or more fuel?

Looks like I have to scrounge up my tuning manual....

[Guest Anonymous]

the number is the size of the fuel orifice, so 50's are richer than 45's.

Popping is often cause by an air leak into the exhaust somewhere, particularly on over-run.

Brian

[Guest Anonymous]

The "F" refers to the size and number of air orifices in the jet. The larger the air orifice(s) for a given fuel orifice size, the leaner the jet. This is because the jet mixes air and fuel, and changes in the relative sizes of the orifices change the mixture.

An F8 jet has a larger air orifice than an F9 jet, so all other things being equal, the F8 jet will be leaner than the F9.

It is not clear that a 50F8 jet will be richer than a 45F9. They may be very similar, or the 50F8 may even be leaner than the 45F9.

Chris B.

'73 ex-Malaga

[Guest Anonymous]

55s or 55 f9 idles should cure your ills. The "f" numbers are NOT sequentially richer or leaner (ie: an f1 might be richer than an f2, but leaner than an f9....)it's very cryptic - consult Pat Braden's book for more specifics on 'em. I remember f8 and f9 being on the richer side though.

I went from straight 55 idles to 55 f9 idles - didn't see much difference in smoothness. The popping folks describe is generally from overly LEAN mixture during transition throttle.