1badgenesis

hey guys this is my first carb motor and this stuff is all confusing to me lol right now my car has a aftermaket 350 in it, mild cam, stock heads n intake and a holly 750 double pumper. i bought the car like this last year had the carb rebuilt around april car drove really nice until the end of the summer on some hot days the car would break up pretty bad but it was only certain days if i remember and then it became fall/ and winter . the car runs amazing again lol but i m worried that once it gets warmer in ny again that it ll runn shitty. whats the best carb for my set up. this is a street car that i just like to have some fun in. the guy that built my car when i got it said the carb might be a little to big

five7kid

iTrader: (14)

It's probably not the carb.

What do you know about the fuel delivery system? The factory used a fuel return to help prevent vapor lock problems. For whatever reason, most "hot rodders" defeat that system with a non-return fuel pump that worked great on their best friend's uncle's '67 Camaro, so they assume that's what their 3rd gen needs, too. WRONG!

You gave us very little information about your car, such as year, original engine, original induction system, etc. A good percentage of 3rd gens came with EFI, and were later converted to carb. If that was the case with your car, that opens up another can of worms.

There's an old saying that 75% of carb problems can be fixed with a set of points and condenser. Of course, that came from days of yore before electronic ignition systems came out. And, of course, all 3rd gens came with electronic ignitions. But, heat is the #1 enemy of electronics. It can cause problems that go away when the heat is removed. So, the old adage still has some validity in that carbs are often blamed for what are really ignition problems. So, a description of your ignition system is in order here.

1badgenesis

hey man sorry the car is 85 z28 i dont know what motor came in the car but i m assuming a 305 carb, i dont know much about this car but it does have a mallory hyfire vi-al ignition system if that does help, it has a th350 auto tranny and 373 gears

five7kid

iTrader: (14)

Okay, not raggin' on ya, just trying to get sufficient information to give you the best possible advice.

Look at the VIN. The 8th character is the engine type. H = LG4 305, G = L69 305, F = LB9 TPI 305. Anything else will be V6. The reason this may be important is the car may have come with an in-tank electric fuel pump. Many swappers to carb just let the mechanical pump try to pull fuel through a non-operating in-tank electric. This makes the mechanical pump suck hard (which they aren't good at), lowers the pressure in the supply line, and makes it more susceptible to vapor lock (especially if they used a non-return type mechanical pump). Another possibility is it does have an operating in-tank electric pump, but they used a cheap dead-head fuel pressure regulator which is hard on the electric pump and makes it overheat.

Still a possibility it's an ignition problem, but there's at least a good possibility it's inadequate fuel delivery.

I really doubt it's the carb, though.

1badgenesis

thanks for the help i checked the vin its a f so the car came with the 305 tpi. i m pretty sure it has a electric fuel bump because you hear it and there is a fuel pressure gauge on the side of the motor so i can run that back to the regulator to see what kind it is? would pictures of my engine be easier?

five7kid

iTrader: (14)

Pictures may help. Of the regulator, especially.

The pressure gauge should be on the line that goes to the carb. Some regulators have a gauge port, which is fine.

1badgenesis

it doesnt have a name on it, but theres 2 lines that go from the gauge that go to carb and then theres a line that goes to this

five7kid

iTrader: (14)

Looks like the proper type of reg. Not sure of the brand, either.

Factory in-tank electric pumps can't be expected to last forever. Getting weak on a hot day is one of the failure characteristics.

It would be best if you could observe fuel pressure when it's acting up. Probably can't do that with that gauge, though. By the time you stopped, got out, opened the hood, and looked, the pressure would probably be fine again.

Where does the pressure sit at idle?

1badgenesis

not sure i ll look when i get home and get back to you

1badgenesis

Let the car run for 10 mins checked the pressure it was at 4 psi

five7kid

iTrader: (14)

4 psi is on the low end for a Holley carb. They recommend 4-7 psi. I doubt that's the problem, but it wouldn't hurt anything to bump it up to 6 psi.