JP84Z430HP

First of all, this is just an interim fix that I want to accomplish, my final goal is EFI. The longer I can make the carb last, the better though, I'd like to get a bunch more stuff done first, like suspension and steering all rebuilt, Body work, etc.....

Here's my car: 355, Fastburn heads, LT4 HOT cam, around 10:1 compression, basically a ZZ430, but built by me.

The problem: The thing is great under light throttle, part throttle, idle, acceleration, basically, everything but WOT. Once I get to WOT, it pulls really hard for about 2-3 seconds (I'm guessing long enough for the air valve to get opened up all the way) then it SEEMS like a lean misfire. I let off just a tad bit, then get back to WOT, then the same thing after a couple secs.... Sounds simple enough to throw some richer rods in it, but that didn't seem to help. I had a set of AX rods here, which look to be pretty rich to me. Is the tip still too big to let enough fuel in? I know the fuel pump is keeping up, it still has pressure when this happens, and it's an electric pump. The problem is also NOT RPM dependant, although, I can't keep the RPM's low with an auto trans!!!!

I have dome a few mods to it, such as allowing the AV to open all the way, new gaskets and cleaning, adjusted the throttle stop to go to WOT, epoxy on the welch plugs, etc....

Should I dig up some other rods? I think the hanger I have in there is a "D" hanger, maybe I need a "B"?????
Any advice is appreciated in advance!

TMX

The first things I'd be looking at, based on the symptoms you describe, are fuel pump volume, float level, and the condition of the fuel filter.

-Bob

Stekman

What is the float level at. At WOT, you could be emptying the fuel bowl.

JP84Z430HP

Good point, I'll have to go back and see what I put it at.

I know I have sufficient fuel TO the carb, pump, lines, filter all have been chacked, or are new..... It's not a BIG fall-off, just start's what feels like a lean-misfire....

RB83L69

Yup, that's a clear-cut case of fuel starvation.

Try a new fuel filter. I'd recommend the nylon screen type, not the paper or the bronze type; if you have to use the paper one, remove the little rubber check valve.

You may also find that a lightweight fuel pump drive rod will help.

A Q-Jet is entirely adequate for a small motor like a 350. They were used on motor homes, dump trucks, etc. etc.; things with much larger engines, and vastly higher fuel requirements. There's nothing wrong with the design of the carb that would prevent it from feeding the motor.

Another possibility is that the pickup tube in the gas tank (part of the sending unit) has hardening of the arteries, plugged with dried-up old gasoline crusties; especially if the car has sat around for periods of time.

JP84Z430HP

RB:
No mechanical fuel pump any more. The 350 block is a 98, and it doesn't have the hole drilled for it. I would've had it drilled, but I plan to be fuel injected some year! I'm using the Carter P4070, the one with a green label. The specs on it: 4-6 PSI, 72 GPH free flow, which I believe is more then I need?

When driving it today, I noticed it smelled like fuel when it acted up. Maybe it's flooding out? I never let it go for very long, just in case it is lean, I don't want to hurt anything!

I still need to check the float level, and verify what Rods I put back in it last time.

spekbikes

hey man, im having the same problem with my quadrajet, i jsut finsihed building up the motor, and it seems to like large primary jets, and lean secondary rods, it seems jumpy as hell on the primary but once my secondary openms up it bogs liek hell, somethings weird! al lyour symptoms sounds simiolar to mine!! hope we come to a conclusion!\

RB83L69

Spek:

Your problem is not at all the same as JP's. His is time-domain; i.e. runs good for a while, then when the fuel in the bowl runs out, it starves. Yours on the other hand is the typical QuadraBog, usually caused by inadequate secondary air valve tension, usually because somebody who didn't understand how the carb works, thought that it would run better somehow if the valve could just flop open. Misadjusting it like that lets in far too much air, which is the flip side of the same coin as too little fuel, both of which are a lean condition, which is what causes the bog.

Try setting it to 5/8 turn.

JP84Z430HP

Ya, that Air-Valve can be touchy!

I still don't think I have a fuel DELIVERY problem, because it is instantaneous that it will pick back up, and I only lift by like 5-10% from WOT. It feels like metering rod issues, but I have tried all of them I have. What is the common reccomendation for a beast such as mine?

Is it possible that the AV is opening too far? I did the trick of grinding away the stop to get it to NEAR vertical. The problem was there before and after that change, (IIRC), but I think it was just a tad bit worse.

I'm thinking about grabbing a spare card out ot the junk-yard and trying it out (after freshening it up a bit of course!)

I still haven't checked the float level, but I remember that I had set it to one of the higher (fuller bowl) settings they listed on the spec sheet (did that since going from 305 to a healthy 355).

I'm gonna quit muttering now, and hopefully I can take a look at it some tomorrow. Today's work on it was new wiper blades (all that I had time to do, and I needed them!)