Too much or too little fuel? ZZ4 - Chevelle Tech
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post #1 of 51 (permalink) Old Sep 5th, 19, 3:55 PM Thread Starter
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Mike
 
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Too much or too little fuel? ZZ4

350 sbc. ZZ4 with l98 heads. Stock crate motor from what I have researched about it. Late 80's I think because of the center bolts on the valve covers? Here is my problem. Falls flat on it's face at initial acceleration and feels laggy all the way through. Previous owner removed the 650 - 4 barrel edelbrock and installed a 750 - 4 barrel holley and (had it tuned). Backfires loud and hard through the exhaust on deceleration. I feel like it's getting too much fuel. New plugs installed so I will be pulling them this weekend to see if that is the case. Thoughts? Also, the fuel pressure guage on the dash doesnt really react to fuel pressure changes on the regulator. If I let it sit at idle after starting it reads 6.5 psi. If I get on the throttle under load it jumps up to 14 psi but wont come back down for like 10 minutes. Bad regulator? Bad guage? This is the regulator it currently has on it. Seems to have a vacuum line, a return line and a feed line to the carb. Any recommendations on a new one?
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post #2 of 51 (permalink) Old Sep 5th, 19, 4:13 PM
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Re: Too much or too little fuel? ZZ4

I dont think the backfiring is from too much fuel.

That being said the fuel pressure does sound flaky. What fuel pump ? Also do yourself a favor and get rid of that glass fuel filter before your car burns to the ground

What are you calling a vacuum line ? The small line that goes to the red "pod" on the firewall is part of the fuel gauge. The pod isolates the gauge from fuel so no fuel is coming into the interior of the car.
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post #3 of 51 (permalink) Old Sep 5th, 19, 4:20 PM Thread Starter
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Re: Too much or too little fuel? ZZ4

Quote:
Originally Posted by BillK View Post
I don't think the backfiring is from too much fuel.

That being said the fuel pressure does sound flaky. What fuel pump ? Also do yourself a favor and get rid of that glass fuel filter before your car burns to the ground

What are you calling a vacuum line ? The small line that goes to the red "pod" on the firewall is part of the fuel gauge. The pod isolates the gauge from fuel so no fuel is coming into the interior of the car.

You just answered a load of questions for me. I assumed it was a vaccum line because it looked like it ran over to the manifold. Im learning so greatly appreciated.

It is a manual fuel pump on the right rear. I can take a picture shortly. As for the glass filter, thanks for the tip. I have heard that a few times already. Do you have any suggestions for fuel filters? Summit had a black enclosed one that I thought looked cool. lol.

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post #4 of 51 (permalink) Old Sep 5th, 19, 5:32 PM
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Re: Too much or too little fuel? ZZ4

I hate seeing Teflon tape on anything but fuel fittings in particular. I wouldn't be at all surprised if some found its way into the regulator or the brass filters in the carb inlets.

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post #5 of 51 (permalink) Old Sep 5th, 19, 5:38 PM
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Re: Too much or too little fuel? ZZ4

It probably is too much fuel on deceleration as it's unburned fuel in the exhaust and can be caused by a number of things. I would get rid of that crappy fuel filter and buy one that will actually flow fuel. As for the carb hesitating on acceleration the Eddy's have a problem with the sec weight opening to soon as it's too light and the Holley, that could be a host of things from being too big for the engine, not enough squirter, too light of a spring if it's a VS model or not enough converter in the car sometimes. My 461 has had the decell problem with a smaller carb at times but fir me it's no big deal at the track, on the street I can see that being bothersome.
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post #6 of 51 (permalink) Old Sep 5th, 19, 5:52 PM
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Re: Too much or too little fuel? ZZ4

Here is what I have on my Car for the Street and Track use ;

- Holley EFI Sniper Fuel Tank https://www.jegs.com/i/Holley/510/19-105/10002/-1
- Dual Russell Braided Hose Fuel Lines (Feed & Return) https://www.jegs.com/i/Russell/799/632080/10002/-1
- Aeromotive 340 lph Fuel Pump https://www.jegs.com/i/Aeromotive/027/11569/10002/-1
- Holley # 12880 Fuel Pressure Regulator https://www.jegs.com/i/Holley/510/12-880/10002/-1
- Russell # 650310 Fuel PSI Gauge https://www.jegs.com/i/Russell/799/650350/10002/-1
- Installed just before & at the Fuel Regulator http://www.jegs.com/i/Earls/361/230106/10002/-1
- Metal Fuel Filter NAPA https://www.napacanada.com/en/p/NGF3033 Alone frame rail Ĺ way to/from Gas Tank

Also have a Moroso # 64943 Carb Spacer Phenolic & Plastic / 4 hole plenum design / ĹĒ thick
http://www.jegs.com/i/Moroso/710/649...oductId=743742


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1/4 = 11.814 et / 115 mph
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post #7 of 51 (permalink) Old Sep 5th, 19, 9:07 PM Thread Starter
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Re: Too much or too little fuel? ZZ4

Quote:
Originally Posted by 68Chevele View Post
It probably is too much fuel on deceleration as it's unburned fuel in the exhaust and can be caused by a number of things. I would get rid of that crappy fuel filter and buy one that will actually flow fuel. As for the carb hesitating on acceleration the Eddy's have a problem with the sec weight opening to soon as it's too light and the Holley, that could be a host of things from being too big for the engine, not enough squirter, too light of a spring if it's a VS model or not enough converter in the car sometimes. My 461 has had the decell problem with a smaller carb at times but fir me it's no big deal at the track, on the street I can see that being bothersome.

I shouldve kept the 650 edelbrock that I sold with my 71 Malibu 307 car recently. I will certainly replace the fuel filter. Any recommendations? Will just keep it in line with the current one.

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post #8 of 51 (permalink) Old Sep 5th, 19, 9:24 PM
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Re: Too much or too little fuel? ZZ4

That pod on the firewall (as was said) is an isolator so that you can run a fuel pressure gauge inside the car. From the regulator is the fuel. On the other side feeding the guage is antifreeze. There should be a small bleeder screw on it somewhere. It may have some air in the line or not enough antifreeze in it.

Mine was quicker with a 650 than 750. But was fine with either.

Check your timing and make sure it is set right. Might be too retarded.

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post #9 of 51 (permalink) Old Sep 5th, 19, 9:38 PM
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Re: Too much or too little fuel? ZZ4

What is the part number of you carb, Holley makes about half a dozen 750ís.

Steve R

Last edited by Steve R; Sep 5th, 19 at 9:40 PM. Reason: X
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post #10 of 51 (permalink) Old Sep 5th, 19, 9:50 PM
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Re: Too much or too little fuel? ZZ4

A ZZ4 is a smooth idling engine from what I've read. Does your car require that exotic fuel setup ?

Why is there an electric fuel pump and all of that fuel-system nonsense mounted on your car ?

All it needs is a basic mechanical fuel pump if it's a normal crate engine.
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post #11 of 51 (permalink) Old Sep 5th, 19, 10:30 PM Thread Starter
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Re: Too much or too little fuel? ZZ4

Quote:
Originally Posted by nashville beth View Post
A ZZ4 is a smooth idling engine from what I've read. Does your car require that exotic fuel setup ?

Why is there an electric fuel pump and all of that fuel-system nonsense mounted on your car ?

All it needs is a basic mechanical fuel pump if it's a normal crate engine.
This is how the car was setup when I bought it. Ive contemplated going back to a mechanical fuel pump.

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post #12 of 51 (permalink) Old Sep 5th, 19, 10:37 PM Thread Starter
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Re: Too much or too little fuel? ZZ4

Quote:
Originally Posted by Steve R View Post
What is the part number of you carb, Holley makes about half a dozen 750ís.

Steve R
The only stamp I see on the carb is 10569 and 80508-8 with I think C496 below it.
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post #13 of 51 (permalink) Old Sep 5th, 19, 10:45 PM
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Re: Too much or too little fuel? ZZ4

What is the stamp on the air horn??

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post #14 of 51 (permalink) Old Sep 5th, 19, 11:01 PM Thread Starter
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Re: Too much or too little fuel? ZZ4

Quote:
Originally Posted by LeoP View Post
What is the stamp on the air horn??

80508-8 with I think C496 below it.
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post #15 of 51 (permalink) Old Sep 5th, 19, 11:08 PM
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Re: Too much or too little fuel? ZZ4

An 80508 is basically a 3310 with an electric choke. They have a metering block on the primaries and a metering plate on the secondaries, your pictures suggest the carb hasnít been modified from stock. It and your ignition could probably benefit from some fine tuning.

GM did a good job designing the ZZ4, itís not going to be a world beater. When tuned properly the performance should be more than acceptable for the vast majority of people.

Steve R
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