Thread: I need help with my Chevy 355 fueling

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Well I can't get a response from the Impala Forums so I'll try you guys. Any help is greatly appreciated.

In my '66 Bel Air, I have a 4 bolt main 350 out of a 1970 C10. Its bored 30 over, RHS Pro Action heads 180cc intake runners 74cc chambers, manley 2.02/1.60 valves, Comp Extreme energy cam .463/.469 lift 262/270 duration, Manley flat top pistons approximately 11:1 compression, Edelbrock torker II intake, Holley 650 double pumper 70 primary/72 secondary, carter super strip fuel pump, GM HEI with accel super coil. Timing is 4 advance at idle (if i remember right) and 35 full advance at 3,000 rpm

When the engine was dyno'd, it ran lean until they put the 70 primary jet and 73 secondary jet into the Holley and when it was in the car it was running really rich, the exhaust pipes were black after a tank of fuel through it and the plugs were black. It started running rough and I went down to a 68 primary/70 secondary and slowly worked my way up. Come to find out one of the plug wires was arcing across. So I changed that and now it idles fine back at a 70 primary. But now with a 72 secondary jet it stumbles when you step on the gas. So I put one size bigger primary squirter, and one size bigger secondary squirter in it, and that helped a little bit but it still stumbles when you stomp on the gas.

The motor was broken in on the dyno, has about 6 or 7 dyno pulls on it, and probably 500 miles in the car. Fuel pressure is between 9 and 10 psi. I've changed jets so many times I'm sick of it. I'd like to be able to stomp on the gas and not have it fall flat on its face. Any help is appreciated.

Try a fuel pressure regulator , to drop the pressure to about 5-6 psi .

Could also check the vacuum advance canister on your distributor, make sure it's pulling some advance in when required... Did you leave the stock springs and weights in the mechanical advance?

I can try the fuel pressure regulator. I was told that 9-10 psi would be fine on a Holley but I have a Holley Black fuel pump i'm going to put on the car, so I'll put a fuel pressure regulator on then.

The stock springs and weights are in the distributor. I replaced the rubber hose to the vacuum advance but i'll check the canister. My neighbor who drag races a 68 Chevelle with a 400 small block/ th350 said that what he did on his car was cut the vacuum canister off and welded the rod where it was.

I should note that when the motor was on the dyno, and in the car for a couple hundred miles, the vacuum canister wasn't hooked up to a full vacuum port. When it started running rough, I timed the motor, and hooked up the vacuum canister to a full vacuum port. That should only affect mileage though right?

I doubt you would notice any difference in fuel mileage... An alternative to locking out the vacuum advance is using one of the adjustable vacuum advance canister's, by turning the adjustment you change how quick the advance comes in. Sounds like the engine likes the advance, it would be worth a try to lock in the vacuum advance arm again. Lighter springs and the different arms will also bring the mechanical in a bit faster.... I would suggest just changing one side of the advance at a time, messing with both at the same time can lead to a lot of frustration!!!!

Alright, I'll get a set of arms and springs off of Jegs sometime soon and try those out. Would you suggest doing both the adjustable canister and the weights and springs, or just the weights and springs?

I think I'd start with the vacuum side, then do the mechanical... Probably doesn't matter which you start with, just remember that the vacuum advance comes in first, should start just off idle, the mechanical advance comes in second and should be all in by about 3,000 RPM.

Are you running an auto tranny? If so the secondaries, being manual, are coming in too soon causing you to bog.

Yes its a TH350

I suggest that you pull the DP off and go with 4160 vacuum secondary carb. DP's and auto trans don't work well together unless it's a full out drag car that you are running at WOT.

How much of a stall converter do you have and what is your rear end gear ratio. A 66' Bel Air is on the heavy side and to get it to "shat and get" from a stop will take some gear and a bit of a stall converter regardless of your carb. The double pumper 650 should be fine and I think your advance is good too. I'd probably gear it with sometinng near a 3.73 ratio range at least. Possibly a little lower. A 3500 rpm stall converter should help as well. Also a 2 plane intake manifold gives more bottom end torque as well but the Torker II single plane manifold should be fine if you are running lower gears in a heavy car.

I don't know who told you that a Holley will take 9-10 psi, but he should be tied to a pole and caned.
Tee off at the carb inlet and run a copper line back to the firewall, then up past the hood lip and onto the cowl. Temporarily mount a liquid-filled, 0-15 psi mechanical fuel pressure gauge onto the cowl with tie-wraps or duct tape or whatever. It's only temporary until you get the pressure under control. Old Stromberg 2-barrels would withstand about 2 1/2 psi, modern day 4-barrels will tolerate between 5 and 6 psi. Don't just put a regulator in the system until you rig up this gauge and can monitor the pressure through the windshield as you drive. Pull it back to 5 psi and I think you'll have a completely different critter on your hands. Any more pressure than that can blow past the needle and seat and blow raw fuel into the intake manifold, creating a tuning nightmare. A carburetor is a carburetor, not fuel injection. You cannot make more power with a carb by raising the pressure.

Like TechInspector stated, dial the fuel pressure back to 5-6 lbs. That is your major problem. Secondly, you have a mismatch of parts in the engine. Automatic transmissions and double pumper do not go well together unless you have a lot of stall speed. Compounding the problem is your intake manifold which is a single plane, and you should be running a dual plane if you want low end torque which most automatic transmissions need. Like others have suggested, fix the fuel pressure first, and then consider upgrading to a vacuum secondary carburetor and a dual plane intake like a Performer RPM. The difference in performance will be like night and day.

Like rumrumm said you need a lot of stall or a total manual valve body to run your TH 350 and a 650DP on the street. DP and Auto tranny = pig.

Okay. I'll get a regulator on there. It has a 2,000 rpm stall, and I'll try out a dual plane intake eventually since I have my 3 other projects to work on too. I have a vacuum secondary Holley sitting on my shelf from a L35 396, I can't remember the cfm. I do want to fix it, but it's not something that needs to be fixed right away. I have an L35 396 out of a 1966 impala that I'm going to build for it eventually, and then the 355 will go in my 1982 Chevy K20. But I will definitely try the advances, the regulator, and probably the intake manifold.