Racing Fuel Systems

Carb is a highly modified 84011-2, 750 vacuum. Runs fine except at complete random, one bowl or the other will flood. Remove needle, blow clean, it's good for a few days and then the other one freaks out. I can't ever find any loose debris in the bowls. Tried multiple different needle/seats with different o-ring material, makes no real difference.

It has nitrophyl floats in place of the 4010-style hollow plastic ones, and also has 4150 float springs added. With the lid right side up and floats hanging down, the springs are set to where the floats are just barely touching the bottom of the needles (the floats are essentially weightless like this but still allow the needle/seat to fully open). Fuel pump is a Carter stock replacement that makes a real honest 6 PSI (unlike the 14 PSI China copyclone pump-like objects that have flooded (haha, pun, get it?) the market).

Am I correct in assuming that, if it's not a saturated float, and it's not too much fuel pressure, and it's not debris in the needle, it can only be bypassing the o-ring?

secondary question: How many more chances should I give this turd before the QJet goes back on, which has never given one single problem even though it's fed by the exact same fuel system, even the very same feed hose and everything?

Nothing wrong with QJs!!!

With the Holley, floats are not going to randomly get fuel logged, sink & cause flooding. Look at float linkage binding, or floats binding/jamming against carb walls.

(I'm about to switch from the dual pattern intake to a Victor Jr, which is the ONLY reason for trying to find an alternative. I did make an adapter, very thin, like .400", that is just enough for the QJ blades to clear the square bore flange - and I'm not crazy about reshaping the flange to suit the QJ bore locations, as that really biases the flow into some runners much more than others. I am definitely going to try it first, though.)

There's no float binding, this weird carb uses a lot of standard 4150 parts (floats, pivot pins, N/S) while still being quite different elsewhere. The 4010 plastic floats are direct interchange with the nitrophyl or brass standard ones. The plastic ones are very prone to cracking though, and when they do, they fill up and sink.

Removing the N/S, blowing clean, and reinstalling temporarily solves the flooding. Until it decides to do it again. If I could live with it long enough for it to get where it's broken all the time I'd be able to figure out what's doing it. But as soon as I touch it it's no longer broken. And it's never fixed itself on its own - I've let it sit overnight and the next day it's still flooding.

Isn't this the reincarnation of the ford 4100 carb which had side hung floats? Summit racing now sells these?
Does this carb use the standard centre hung float and float spring? I have a kit for one of these and it doesn't even mention the float spring. Go figure.
The ford 4100 carb was a great carb but I can only imagine that Holley would screw that up.
What did you mean by highly modified?
Are the throttle blades open too far causing nozzle drip?

No, this uses standard center hung float stuff. You're right, in stock form they have no float spring. And without the spring they do not work with more than about 3.5 PSI fuel pressure. This one, now, should be comparable to any other 4150 in regards to fuel pressure. Same nitrophyl floats, same pivot pins, same springs, same standard .110" Viton N/S.

Yes, Summit bought the design. I have not seen one of theirs in person. Holley finally figured out the design by the time the -3 versions (real rectangular transfer slots; pre -3s had drilled holes instead) were built but the public had already written them off. (they never did anything about the float-spring-missing, though). They couldn't escape the bad reputation and shelved them. The 84011 (vac) & 84013 (mech) have 1-1/2" venturis... so quite a bit bigger than a 4150 750.

'Highly modified' in that all the bleedsnfeeds are adjustable now, has homemade idle tubes with the IFR at the bottom instead of in the top of the clusters, homemade annular inserts, and emulsion package has been changed. But none of that will affect the float & N/S.

When I say 'flooding', I mean an inch of fuel standing on top of the butterflies. Very mild cam in it at the moment, so no throttle blades open too far. This is an inability of the float to stop fuel going into the bowl.

It has flooded with plain N/S from a rebuild kit with the black o-rings, it has flooded with plain N/S with the tan o-rings, it has flooded with N/S using Viton 008 o-rings from McMaster that I swapped in. It will be 100% fine after reassembly, then a few days or an hour later or after driving one single block one of them will overflow again. Bores in the lid below the N/S threads where the o-rings sit are shiny and clean and undamaged.

I'm pretty sure it's not pressure-related as it will be perfectly fine for a while until it suddenly isn't. And fuel pressure is constant whether idling or driving. Seems like if it was going to not be happy with 6 PSI it would not be happy instantly, all the time.

Move down to 5psi

If this were a plain 4150 with all standard floats & needles, would you still blame the fuel pressure?

If you had a stock, simple, easy to work on fuel system, how quickly would you jump to the 'put a pressure regulator on it' solution?

If 6 PSI is too much for it, and the pressure is always 6 PSI, why does it not flood all the time? Why is it OK with 6 PSI for hours or days at a time? It's not heat related, it's not vibration related, it's not runtime related. Sometimes it floods when cold right at startup, sometimes it's OK for days and many miles.

A mechanical pump can't really make more pressure than what the spring makes. The cam lobe retracts the diaphragm for the intake stroke, the spring pushing the diaphragm back down generates the pressure. Something could stick or hang up and make it put out less pressure, but not more pressure.

I'd rather test this by sticking a plain 4150 on it rather than cutting up the fuel lines to install a pressure regulator I don't already own.

Found this on a Corvette site. Might shed some light on your problem.

"The Holley technical data site says that the plastic floats ride higher than the Nitrophyl floats and they give a different "dry" setting for them using drill bits as a pin gage. I don't have it in front of me right now but it's actually quite a bit of difference since I've read somewhere that raising the float level 1/16 inch actually results in the fuel level rising 1/8 inch. Don't know if this is true or not - doesn't really make sense to me since dry - hung settings are usually on the outer toe or middle point of the float.

I think these are Nitrophyl floats but not sure???

From the Holley tech sheet

Nitrophyl secondary float dry adjustment - 13/64 inch on the heel of the float (bottom)

Duracon (plastic) secondary float dry adjustment - 5/16 inch on the heel. "

Hope it helps.