I recently bought a zz4 350 swapped Berlinetta that’s been having some trouble running and driving. Originally the motor had a q-jet that was swapped for a Holley 0-80508s and msd ignition system. When I bought it I was told it was never tuned for the new carb and that was its main problem, only after making the adjustments it still seems to be having an issue. The car sputters down to a stop after putting it in gear and under load unless I keep the rpm up. It also will stall out at idle on occasion, my first guess was a fueling issue and after putting a pressure gauge on the fuel log it stayed reading zero psi. I redid the fuel lines inside the engine bay as well as a new fuel filter and Holley 12-880 regulator. I put the gauge at the regulator and when priming the system the gauge read 3 psi and dropped down to zero and stayed at zero. At this point I believe I have a fuel pump that needs to be replaced but wanted to get input on any other possible problems and recommendations for parts. Any advice would help, thanks.

 

Sounds like the fuel pump is out, so that's a good place to start.

Next, I'd take the MSD ignition system, toss/sell it, and put an OEM HEI on there. That is another area where you can eliminate gremlins as that motor doesn't need any more than a stock-type ignition set up.

After you've done that give it a once over, check the timing, tune the carburetor, and be on your way. The Holley 750 should play nicely with the ZZ4 once you get it tuned right.

 

thank you for helping, do you happen to have any recomendations for brands or part numbers. And I’ll definitely look into replacing the ignition system.

 

I run a holley blue pump right outside the tank on my car, but any standard replacement for the in-take pump should be fine.

Ignition parts you can go one of two ways, you can find a stock-style replacement (i.e. just go to autozone and say you need a whole distributor for an 86 camaro) or go with a large-cap HEI. For large cap HEI parts I recommend AC-Delco, should be easy enough to find. Just remember for that option you're not going to be looking for a distributor for an '86 Camaro. When I'm buying large cap HEI parts I usually narrow the search down to some 1976 model carbureted V8 (like a chevy K20, for example).

 

Davis unified is a good distributor

https://www.summitracing.com/parts/dui-12720bk

 

If the car still has a fuel filter, check that before dropping the tank for a new fuel pump.

 

I could only find one in the engine bay, but I’ll definitely take a look before dropping the tank.

 

Thanks for the help and recommendations, I truly appreciate it. I’ll find a in tank replacement this week and hopefully get it installed soon. I’ll keep tabs on the thread in the meantime and update when I get the parts installed. Again thank you all for the help.

 

I have a large cap HEI takeoff distributor from my ZZ6 crate engine that I would be willing to sell. Brand new, never used, complete with cap/rotor and coil. PM me if interested.

On the fuel pump, it likely only has the mechanical pump on the motor and none in the tank. Some of the L69 305 HO motors had a both low pressure in tank electric pump along with the mechanical pump on the motor. The LG4 low output 305 didn't get the additional in tank pump until 1987. Change the mechanical pump with a stock replacement and change the fuel filter and see what that does before going further.

 

I see no mention of the carb setup... Like what jets are in it... Tuning a carb is not just twisting a screw or two... It has to have the right fuel flow for the air and the load. It may be set up too lean... With jets that are too small...

I don't know Holley carbs... I am a qjet man... But I do know that the right internals make all the difference...you have to make changes there and then check performance. A carb is not just a carb.... Read up on metering changes to the carb. All the fuel pump changes in the world will do nothing if the jetting and mix is wrong...

 

the location for the mechanical pump has a block of plate from factory according to a spec sheet I found online. In that location was the mounting bracket for the old FPR.

 

from my understanding when buying the car, the carb was pulled from the box and put on the engine. This is from the Holley spec sheet. Being new to all of this I don’t know if this looks like it’s good or not.

 

I have a 385 fastburn in my car topped with a 750 double pumper (so a ZZ4 with different heads, breathes a little better). The 750 you have can be tuned to work well with your motor but the problems you've described should be addressed in the order many folks have previously stated on here. You can absolutely go down the carb tuning rabbit hole, but it's close enough now (and may be fine altogether) but you can't tune the carburetor properly until you know that all other systems are up to snuff.

If you tune it and your timing is off. . .you'll have to retune.

If you tune it to work with a dying fuel pump. . .you'll have to retune.

etc.

 

An 86' Berlinetta with a 305 would have been a 4bbl carb and would have had the mechanical fuel pump there. The blockoff plate would only be on the fuel injected 305, which were only available on the Z28 and Iroc-Z.

Your fuel system may be modified from stock.