Holley 750 CFM Ultra Double Pumper or Quick Fuel Technology SS-750-AN 750 CFM Street?

[RedHawk]

Originally Posted by vector1

IMO that stumble is the transition from idle circuit to main circuit. Most everybody has forgot how to set up a carb. I did some research on the carbs for the Boss 302 and the holley carbs of the early 70's late 60's along with whatever else info was available.

I have an a/f gauge on the JBL so I could watch what was going on. I came to accept the wild swings of the needle as normal for a carb but wasn't really satisfied, tried quite a few setups and have all the tools and parts to make the adjustments.

After doing the research above, went out to the shop and found a Holley 750 with center hung floats no less that came off a Ford 400M.

Here is that setup on the 400M, and this was in a truck btw, so it should be useable in a lightweight cobra imo. I use it on a 408 and a 351 with small adjustment to the main jets. The a/f gauge needle is so smooth it is unbelievable.

Primary main jet 73
Secondary main jet 80
IFR .029
IAB .070
HSAB .029
PVCR .052
PV 6.5

No siphon breaks on the primary block, .026 siphon breaks on the secondary block

5 hole main well top to bottom--.026 BL .026 BL BL (two hole main well would be both .026)

With this setup in a Holley 750 HP except 74 main jets all around on the 408 netted cruising a/f of 13.5-14, little rich. On accel it would richen to 12.5-13, very smooth and no jumps.

I would try the exact same thing on your 351 with blower, which is probably close to the 400. Should light up your cockles.........

hth

ps, this setup pulls all the way from idle with no problem, note the .029 HSAB and main well settings are important.

Thanks!
See I thought the stumble precipitated jetting up on the secondary to 86 so your saying down to like 80. I'm in Dallas.
I hope you don't mind but I attached pictures of plugs 4-8. From my research it looks the burn marks are closer to the threads meaning too much timing. Also I am reading that more than 3 rings showing a glaze from the top also indicates too much timing. Thoughts?