MBDiagMan

kalli might be onto something. There might be a need for stagger jetting.

You are very wise to keep it running fat until you can get further into the problem. You DON'T want this engine to even dream of leaning out.

Even though I didn't pick up on the blow through part, the principles that I spoke of seem to all apply

68dustin

well jetting is very easy to do, so what do you guys think of jetting the rear up to? should i just do standard 2 at a time and see how it feels? i cant find any carb # on the horn since it's been shaven. It looks like my old 4150 double pumper that i had on the car before. THe main body has a big holley logo on the side if that helps.. tonight when i get off work i will step up those rear jets and see if it improves...

Driving situations:

stop light first gear hard accel from dead stop (car accel strong with no hesitation until you switch to third, small hesiation then pulls hard again.

driving around in any gear with rpms steady around 3k, smash on the gas hard or even drop down another gear (no hesiation)

driving around lower than 3k, smash gas then hesiation then take off

urban_cowboy

So your hesitation is basically at low rpm? Have you tried a quicker pump cam curve? The pink cam pumps more fuel over the course of the throttle movement, but it is not very quick.

See the chart below.
http://www.carbdford.com/tech/Holley20PumCams.gif

kalli

well ... you could always compare the plugs front and back straight after a WOT run (no idling/driving after that. run. shut off engine. check). you can as well take the rear bowl off. if there is no powervalve in there (i assume your carb has only one in front metering block), then I would go 6 sizes up in the back (back only). If the lot is too rich, reduce front and back by two at a time from there.

This is my personal opinion so someone back me up onm that :-) can't go bad but loose a bit of power going too rich ...

68dustin

Sounds good guys i will get back to you. Is the blue cam or green cam the one with the most aggressive pitch?

67mustang302

Jetting on Holley type carbs is usually about 6 sizes bigger in the rear. That's because the power valve channel in the front accounts for about 6 jet sizes worth of fuel flow. BUT that's only if you don't have a rear power valve, and it's also going to depend on what the air bleed settings are and booster sensitivity as well as the emulsion circuits. I'd go to whatever the factory jetting was + 1-2 sizes front and rear. So if the factory jetting was like 68/74 try 70/76 for instance. Keep the jet staggering the same, if you need to jet down, go one size down on both the front and rear.

Get the idle set right and then get the WOT jetting correct, probably want to keep WOT AFR under 12.5, low 12's is a good safe zone for light boost on a blower, or you can even go high 11's for extra safety as long as it's not fouling plugs etc. Then put the wideband on and drive around and figure out WHERE and WHEN it's lean. At part throttle accel, full throttle accel, what rpm etc.