I have a 1981 Z-28 350 bored .60 over. Semi agressive Bracket master Cam Holley Fuel pump and Holley 750 carb. I began having problems from the time I switched from a Edelbrock carb to the Holley. Motor seemed like it wants to fall on its face at high rpm while going down the road. Tried all kinds of timing changes with no success. We have kinda narrowed it down to being a possible fuel problem. I ended up getting a pressure gauge and it was reading about 6psi at idle. Took it out for a drive and then checked the psi again. It was then reading 0. Engine cooled off and fired it back up and it was then reading around 5. decided maybe it was the fuel pump. Replaced the edelbrock pump with a 80gpm holley. Fired the engine and was reading around 6 again. Drove it and like before fell on its face and got back and the psi was at 3. Checked all fuel lines fitting and everything for leaks and tightness and everything is fine. The holley that I bought was used so is it possible that the carb needs a rebuild or something with the carb that is causing the fuel system to not come up to pressure? as of right now the fuel pressure is hanging around 3psi

 

Has anything been changed from stock with your fuel lines, mainly the vents? Could be the tank isn't venting and you're creating a vacuum. Next time try checking the fuel pressure like you did, then remove the gas cap and see what you get.

 

Nothing has changed from the point of the fuel tank to the fuel pump. Everything had worked fine untill I changed to the Holley Carb. I have even tried disconnecting the line going to the cars fuel tank and running a small line into a gas can to see if it may have been sucking air somewhere in the fuel lines. The pressure still stayed at around 3PSI. I will try the gas cap thing tomorrow just to check and make sure. Thanks

 

That is where I would look... I am not up on all the Stuff for the 81's but I know they had a computer controlled Qjet, I don't know if the computer controlled the Vent system too... If you are still getting a low reading after that Drop the tank and see if you have junk in the tank or if the sock on the pickup is plugged with junk.

Welcome to the forum by the way!!!!!!!!!!!!

 

I went out and fired it up and took the gas cap off and it still was at around 3 psi. I agree that the sock inside of the tank could be plugged but with me running a fuel line directly into a small gas can kinda eliminate that being the cause if the problem was still there when I did that? Or will that really not tell me anything at all? And thanks I think I will be around the forum very often haha!

 

Then it sounds like you may have an obstruction in the fuel line, anywhere from the pickup in the tank to the pump.
Is there an inline fuel filter between the pump and tank that might be old and clogged?

 

No there is no inline filter other than the one that I have between the pump and the carb which is all new. I have been looking around online and I have seen that 1.5 inch fluid filled gauges are worthless when they heat up. So i am thinking I may not have a pressure problem after all. Has anyone ever hear of that problem with gauges? I am back to thinking that the motor is falling on its face because of an issue with the carb. Maybe it needs to be rebuilt since it was used? Seems to be leaning out when it is under load and sometimes causing the temp to hang around 220 degrees.

 

I haven't had experience with a liquid filled fuel pressure gauge. I had a non fluid on mine, and it started to leak internally after a couple of months. However my liquid filled dash gauges work fine.
Have you checked your float levels yet? If one or both are low (or high), it'll give you a stumble off line. Or if they're set too low, it'll starve the engine at higher rpm's.

 

Ok, I am thinking they are right the liquid filled gauges mounted in the fuel line at the carb can fail and do!! Checked pressure with a vacuum/fuel pressure tester and it was fine. Right at 6psi at startup and after warmup and driving. Put the Edelbrock carb back on and went for a drive. Never missed a beat. So it sounds like to me the Holley needs a good rebuild cuz something isnt right with it!

 

Just as a safety reminder, fuel pressure gages that bring the fuel right to gage mechanism should not be used in the passenger compartment. If the gage leaks, gasoline is going to get squirted in the passenger compartment, and there is a good possibility it may stink up the interior, or even go on fire.