Home Forums Gear Hunting Trucks and Four-Wheel Drives Anybody familiar with old Chevy big blocks?

I'm sorry I haven't opened this thread until now. Tzone brought it to my attention.

Please leave your timing and all ignition related items and adjustments alone. Don't go chasing gremlins that aren't there.

You have a fuel problem. I saw it from your first post and every post you have made since your initial post confirms it.

You are flooding, plain and simple.

Your black plugs, the sluggish running, the heavy fumes, having to hold it open to clear the cylinders to get it to start.

Rich, rich, rich.

You have gone down the right path on your own with fuel pressure gauge and regulator, this tells me that you also suspect a fuel issue.

Mechanical pumps like you have installed usually aren't going to give a problem with overpressure that will overpower your float unseating your needle and flooding your carb.

I do like around 6 PSI myself for a street application where your engine is sucking it's air through a carb.

Overpowering your float with too much fuel pressure is the first suspect and possibility. It's more common in cases where an IFI set up with elect fuel pump has been replaced with a carb but the guy is still running the old efi pump.

Do you have an edelbrock 4 barrel like you spoke of earlier? looks like an old Carter AFB?

does it look like this?



This one pictured has an electric choke, does yours have that or is it a manual choke?

here are a couple other possible carbs you might have on your big chevy.

holley:



this is a rochester quadrajet:



Please tell me it's not that ugly sumbich you have on your engine....

Check your engine oil too gruff, pull the dipstick and see if the level is high, smell it and see if it smells like gas.

If your old pump was leaking they can leak into the engine and put fuel into your oil. It's a diaphram that causes leaky fuel pumps, if the diaphram cracks then fuel leaks through to the dry side of the diaphram. Usually there is a weep hole on the dry side that allows the fuel to leak outside of the engine but gunk or other things can cause it to basically have "internal bleeding" as in, the gas leaks into your engine block instead.

great suggestions northern dave. But why the hate on Q-Jets?

Shortest answer I can provide is... I'm a Ford guy lol!!

That being said... I actually had a Q-jet on my 360 ford in my plow truck until just recently.


Q-jet in all honesty is a remarkable fuel delivery device, it stands far out from the croud of conventional jet and power valve metered carbs.

But, it can be a love hate relationship. High maint IMO.

If gruff does have a q-jet, I'd suggest running that fuel pressure in the 3-5 psi range, no more than 5.

I'd also suggest he look at the float first as the plastic foamish floats are kind of notorious for becoming saturated and not being able to close the needle. The needle has a wire clip that has to be installed correctly as well. it is very common for q-jets in particular to have this spring installed incorrectly. Also the welch plugs often leak in these carbs, it was common for them to be installed and also JB weld sealed on rebuild to help prevent leaking.

We'll let gruff come back with an ID on his carb before I go dishing out too much trouble shooting though.

I won't be able to look at it till tonight, but I'm pretty sure it matches the Edelbrock in the top picture. And it has the electric choke. Right after I did the engine swap it would start and run, but after a while die out. I checked the choke and it wasn't opening even after the engine was well warmed up. So I bought a new thermostat, but either didn't put it in right or something, so I ended up wiring the choke open and running it like that for awhile till I took it to the mechanic. I specifically mentioned it to them, and I know they replaced the wire to it (old one showed hot when the key was on so I don't know why it was bad) and I'd hoped it was fixed. As to the leaky fuel pump, I honestly don't know where the gas was coming from. Sometimes it would be a real steady drip, which naturally worried me, but then it would stop and wouldn't leak for several days. But it wasn't an all the time thing. It was coming from the pump though, and not just running down the fuel line from higher up. I have to add oil regularly as the rear seal is leaking. I'll check for a gas smell tonight. I would have loved to replace it before I put it in the new truck, but I was crunched for time with my buddy and so on his advice I just figured I'd add oil every so often until such a time as I either acquired the right tools and know how to pull the motor again a do a whole overhaul, or saved enough pennies to pay a mechanic to do it.

The Q-jet is a great carb when they are right...when its time for a rebuild..they are a nightmare!!

I'm with you Dave, also wish i had seen this thread earlier. Its a fuel issue, too much...way rich!

I do hope its an Edelbrock carb, it can be rebuilt with his eyes closed!

Man, I love this site! You all you guys are a big help.

True, the Edelbrock/Carter (I call them Carters, cuz that's what they ARE...Edelbrock bought the rights and started making them years ago) are way easy to rebuild. Anyone can do it. I would buy a rebuild kit online and do it yourself, as carb shops get an ungodly amount of $$ to rebuild carbs. Case in point: I have a one barrel Holley model 1904 on my '60 GMC 4x4 305 V6. Carb shop wanted $175 to rebuild it!!! I bought the rebuild kit online for $38 and did it myself in about 30 minutes!

One other thing I was thinking about...without going back and reading the entire thread...I had my 64 Suburban act like it was running out of fuel at odd times, not all the time. Turns out it was the rubber fuel line from the fuel pump to carb had a lengthwise slit in it from age, and would allow air to enter, causing all sorts of hard-to diagnose driving issues, as it was not a consistnet problem. Perhaps look at your fuel lines carefully to insure they're not in bad condition? I tell ya, by looking at my fuel hose, it wasn't obvious it was bad, until I started flexing it and saw the slit. Just some more things to check that are free! Good luck!

If it was almost anything but an edelbrock I'd say power valve.... but sadly the edelbrock doesn't use a power valve...

But that does simplify it a bit.

Check your choke, see that it is opening when warm. That black plastic round thing on your elect choke side has a bi metal spring inside of it. When the spring heats up it loads the choke plate shaft twisting the plate open. the spring travel can be adjusted by loostening the screws (usually 3 of them) that clamp the black plastic housing in place. You can loosten the 3 screws and dial the plastic "knob" clockwise or counter clockwise. It will say "lean-rich" on the knob telling you which way to turn it.

You might need to turn it in the lean direction to help the spring flip the plate open all the way.

But you'll want to test this with a hot spring and a cold spring, you don't want it would too tight in either direction. If you have it wound too lean then it won't choke fully or at all when it's cold and you need the choke closed.

If you know that your choke is working then I'd go after idle mixture screws next. those are the 2 adjustment screws on the front of the carb. Take a screwdriver and turn them all the way in making sure to count the number of turns for both screws. This way you can go back to where it was set in case this is not the issue.

Some carbs find the right idle fuel feed at 1 turn on each screw, some like as much as 5 full turns, there is no one set rule.

I'd take a stab at saying you might settle in at around 3 turns each but I wouldn't bet on it.

Count your turns on both screws to turn the screws in until they stop, write the number of turns down. Figure an average for both screws (left one is 4 turns, right one is 3, go 3.5)from all the way in (closed) turn them both out to your average number between the 2 and start there.

With the truck running start turning them in and listen for the idle to clean up and rpm to rise. Go half turn in on both, half turn at a time. Keep the adjustments even for the 2 screws. See if you can find a sweet spot.

Find your cleanest, highest RPM idle setting now with 1/4 turn adjustments on each screw, (fine tuning) find the sweet spot on a warm engine then go out from there a 1/4 turn on each screw and leave it.

Hint, if you can turn the screws in all the way and the engine still runs, then it's flooding inside and you need to go after float/needle/seat.

My thinking here is if it was weak on fuel supply with a bad pump, someone may have been trying to compensate by spinning the idle mixture screws out beyond the norm.

Thanks man! I'll get after it tonight. The thermostat on the choke, it warms up via the hot wire right? If so how long after the key is turned should it take for the spring to expand and open the choke? Then with a hot spring I can adjust it till the choke plate is open, then check it after it cools to see it closed. If I understand it right? FWIW one of the things I did when it started acting up this most recent time was wire the choke open on a warm engine and it did not help with the running rough.

Ok, that makes sense to me then. I wondered how it could go from adjusted and running to out of adjustment and not running without me tinkering.

I'm scared to get my hopes up, but that really makes sense to me. All the issues started when I replaced the blasted pump.

the stuff I explained just now is still good stuff to do regardless... but...

Since you now have a fuel pressure regulator do me a favor and try getting your fuel pressure down under 5psi at engine idle rpm (750-ish) and see how she acts.

You honestly don't need more that 3 psi even if you were making wide open throttle runs on 1/4 mile.

This all started when you switched pumps.

that should always be the first question when trouble shooting "what did I change or do different that might have caused this"

Try that first, fuel pressure.

Alright, will do. I'll put it back on tonight and crank it down. I'll post again this evening. Thanks again Dave.

I don't think the AFB (edelbrock) likes much if anything over 5 psi, and like I said, 3 is really enough.

If she still actually floods with low supply pressure and good choke function and good idle mixture setting, then you'll have to go after the float/needle/seat stuff.

Maybe just a little chunka dirt in the needle/seat area from the pump change out. Easy to get a little crusty crud into a line when doing that. It's usually filthy down by them pumps.

I tried to tun a 650 Eldebrock on my 78 camaro with a 350 in it. I had nothing but problems with the acc. pump and needle seats. I was having the same problmes you're having. I bought the carb new and it did fine for about 6 months. I switched to a 650 holley and never had any trouble again. I may have gotten a bad one but the fuel pressure may have been the problem all along like Dave said. I never thought of that.

They have 2 floats, 2 seats, 2 needles... fuel bowls are on the sides left and right. Easy to figure out when you take the top off the carb.

Yea I know, had mine apart several times it just never crossed my mind about fuel pressure. That was over 20 years ago and I was just learning how to work on them. When I read your post I said to myself that was the problem most likely but that was a long time ago. You learn something new all the time. Where were you 20 years ago.

20 years ago I believe Northern_dave was serving his country in one of those uncomfortable sweaty lands.

Yeah, I know it was a rhetorical question...

John

yeah you is right John. LOL!

but when I got home I slapped a brand new 600 cfm edelbrock on my 327 chevy which i still have today.



For me it was always kind of a toss up between the edelbrock of the time and the current 4160 plain jane holley single feed vac secondary 4 barrel.

I had one of each at the same time, both new.

I still say I liked the holley just a little bit better.