Racing Fuel Systems

This is also posted on another forum, hope that's not frowned upon?

I have a Quick Fuel SS-850, it's basically a niced-up 4781. I've attached a spec sheet from Quick Fuel.

I have a 65 GTO, 4 speed manual, 3.54 gear, 28" tire. Dual plane intake, 236 @ .050 hyd roller, and 1 7/8 headers, edelbrock heads, 505 CID, 4.35 bore, 4.25 stroke, 10:1.

Running at 60 MPH, 2700 RPM or so, I see about 12.5 to 1 AFR on the wideband. I'd like to lean that out a bit. I am happy with the WOT numbers.

Downleg boosters, 80 primary jet, 86 secondary jet, .069 PVCR on the primary side, .093 transfer slot restrictor.

Do I:

(a) Jet down the primaries and increase the PVCR,
(b) Reduce the primary transfer slot restrictor, or
(c) drink a beer, don't mess with a car that runs good, and go for a ride?

Main jet is easier to change, drop it 2-3 sizes to start with. That'll at least tell you whether it's still on the transition slot at that speed/RPM (60 MPH would lean towards no, but RPM leans towards maybe) or on the main circuit. No real change = reduce the IFR and/or embiggen the IAB.

WOT is good?

I’d go a .034” IFR to begin with.

Oh Lordy, I just now looked at the spec chart... .037 IFR/.070 IAB is way way too rich. Idle & t-slot fuel are not dependent on carb CFM (or even engine HP/displacement for the most part), big carbs do not need megahugelarge IFRs like that.

For reference a Holley HP that comes stock with .035 IFR & .072 IAB is too rich at light/part throttle.

You'll probably need to put a real primary pump cam on it after you get the IFR straightened out, if it still has the pink cam. Blue/green/orange are for carbs that are lean enough to cruise nice, pink cams are placeholders to stop the arms from falling off during shipment.

I played with the IFR's previously and went back to stock, it was soft just off-idle. Is there any harm dropping to a .081 transfer slot restrictor?

About 90% of my driving is cruising country roads between 50-60 mph, I feel like if I could go from 12.5:1 to 13.5:1 under those conditions it would be a nice improvement. Leaning it out under other conditions isn't really a priority just yet.

Im working on same issue 80513 holley currently .035 ifr 073 iab idle is real good mix scrws sensitive afr 14.2 if afr accurate with big cam lots of overlap
Cruise in 3 rd & 4th 1800-2000 13.5 - 14
In 5th at 2000 15.7-15
With .082 TSR

Going to try a .078 TSR to see if I can 3& 4 th gear cruisin leaner
May try .033 IFR at some point
My cam os 250/260 @.050
Prior to this I jetted down 3 steps from the 84/94 when started street driving car no issues at WOT
FWIW