High speed air bleeds

[cv67]

How do you know when to go up or down vs jetting?
My idle circuit was lean so went down a few sizes is fine.
What does one look for wiht high speed bleeds? Or what symptom I should say?

[Walter R. Malik]

How do you know when to go up or down vs jetting?
My idle circuit was lean so went down a few sizes is fine.
What does one look for wiht high speed bleeds? Or what symptom I should say?

Changing the jet will change the richness or leaness; changing the air bleed will also change the fuel CURVE along with the mixture ratio; idle or high speed.

[jmarkaudio]

http://racingfuelsystems.myfunforum.org ... ?f=25&t=42

[#84Dave]

Three sizes of main air bleed jets = approximately 1 main jet fuel size. -Dave-

[cv67]

Hmm sounds like I should leave as is til I get a wideband on and tune from there.
Meaning see what the A/F ratio is doing upstairs

[Eric68]

If the engine is a little lean on the top end, then go tighter on the high speed bleed. If the fuel curve is flat and the carb responds to jetting changes then I would leave the bleed alone and give the engine what it wants for fuel with the jet. Someone (hopefully) designed that carb and its fuel curve so I always hesitate when changing high speed bleeds.

If you do decide to change bleeds, a .002 or .003" change should be noticeable (about a 2 jet size change in my experience) but that depends a lot on the booster, emulsion configuration, and carb size too. Also, keep in mind that going smaller on a high speed bleed may make the engine a touch leaner on the bottom end too since it is restricting emulsion air (less lifting action from the emulsion air at low RPMs).

If an engine is not responding to jet changes or bleed changes then take a hard look at the jet diameter vs. the exit channel diameter. Sometimes metering blocks with the wrong (too small or too big) exit channels get installed on a carb. This makes the exit channel the metering orifice instead of the jet and air bleed.

Hope I didn't go off the tech-geek cliff with this post and you find it helpful!

[Doug Schriefer]

Your main jets and air bleeds do different things. There is NOT a direct correlation between changing jet size vs air bleed size. The simplest way to think about it is to look at a funnel. The small end is idle, while the open end is WOT. Changing your main jet will change the size of the funnel (ie larger jet larger funnel, smaller jet smaller funnel) Changing the bleed will change the shape of the funnel. A larger bleed will draw less fuel (Picture a transmission funnel) where as a smaller bleed will draw more fuel (such as a wide mouth fuel funnel)...