[chevyrestore]

Hey everyone. Ive got a 1980 454 in a 59 chevy truck. The engine began running rough a while back, not too bad, and its slowly gotten worse to the point where its time to get it figured out.

I just checked for a bad head gasket with the combustion leak detector and it passes and the plugs looked decent as to show no bad head gasket.

What its doing is when I first start it in the morning it cranks a lot before starting up as if the carb had been drained. Once it gets going the idle is very very harsh and low but on its own after a few minutes it raises and smoothes out a little but still idles very rough.

When giving it gas it sputters a little and shakes more than it should. Once its at operating temperature its much much better but I still feel a little shaking and sputtering. My question is since the head gasket passed the test what should be done next?

Should I condemn the carburetor to be rebuilt? Its an edelbrock performer 1407 and had been used lightly for about 8-9 years but did backfire a few times so maybe that damaged something?

Anything I should do before ripping the carb off and taking it to the rebuilder?

[2wld4u]

fresh gaskets is never a bad thing so yes Id rebuild the carb regardless..

Id check the oil to make sure it does not smell of gas.. thats the first thing Id do... If it does...do not crank it again untill you find out why..

[cdminter59]

Do you have a pressure gauge you can check the fuel pump with or disconnect the line, put into a bucket and spin the motor over to see what volume is coming from the pump. Check distributor cap and wires. Pull the carburetor as a last resort.

[chevyrestore]

pump, cap, and wires are all new and look good. Oil does not smell like gas. Timing is set at 12 deg BTDC with vacuum advance disconnected and plugged.

[2wld4u]

8-9 years driven lightly indicates its sat alot.... you might want to make sure all rubber hoses are in good condition and that you have no leaks etc... and as I was saying sitting for long periods I would either replace or rebuild the carb.

[chevyrestore]

all of the hoses are good, I replace them every once in a while just to be safe. It didnt really sit a lot, I just didnt drive very far very often, I drove it about 4 miles per day while it was running good and this slowly started to happen in that period of time which leads me to believe its not from sitting for periods of time.

[66GMC]

I know that it's human nature to point fingers at the carb first.

But I believe that you really need to be sure that all of the mechanical and electrical components are in good working order before you condemn the carb. Compression test? Valves are in good shape?

A fuel delivery test has already been suggested, and I agree ... whether the fuel pump is new or not. (A new pump can't pull fuel through a plugged fuel tank strainer or fuel filter.)

I'd also be looking for vaccuum leaks and crumbling vaccuum hoses or even rusted (or plugged) steel vaccuum lines. Spray a little brake clean along the edge of the intake to check for leaking intake gaskets. (Make sure you're in a well-ventilated area first)

Assuming this to be a stock engine with HEI ... have a *real* good look at the distributor rotor. They're somewhat infamous for arcing and burning a hole right through the center of the rotor to the distributor shaft. This occurs when the resistance builds up in the plugs or wires.

I'm not an Edelbrock carb guy ... do they use a bronze or paper filter on the inlet?

How about the choke? Is it adjusted and functioning correctly? Black smoke coming out the tailpipe? If dual exhaust, is the misfire prominent on one bank?

The key is diagnostics. If you think that you've ruled out everything else, try swapping carbs or othe components with a buddy (the "known good component" approach.)

[chevyrestore]

Ill give the vacuum leak spray a try and ill check the rotor. This is a high output motor but nothing insane and N/A. The plugs and wires are new, cap and rotor are semi new but havent done a visual on it. The vacuum hoses themselves are all new and tested, new fuel filter and its clear so I can visually see its clean and not blocked (good fuel flowing through it also)

Its a manual choke and not hooked up to anything. Not sure on the carb gaskets. No black smoke from the tailpipes ever.

[454C10]

Did you change the cam? Because it sounds like a cam going flat. Pull the valve covers and start it up. Look for the rocker/s not moving as much as the others.

A compression test would also be a good test to do.

[chevyrestore]

Compression is good and I did not change the cam since the motor was built.

[H D]

Try a different type of fuel filter.
That clear filter may not be flowing enough fuel to the carb.
I had this very thing happen with a clear filter trying to feed a thirsty
460 BBF in a 1978 Bronco. Good luck
H D

[454C10]

so, you are saying it is a stock cam?

I would still check for rockers arms not moving as much as the others. I have had a few issues over the years with BBC's and cam lobes.

[chevyrestore]

its a stock cam but forged so its not the OEM style cast iron cam. I drove it today to get some more info for you guys and I noticed that when im on the freeway just cruising it runs like the healthiest engine in the world. When I accelerate from a stop or theres a load on it like under acceleration thats when the sputtering/hesitation is. Other than that like I said when im cruising even up in the 80s-90s mph it runs awesome. Would that point to something specific?

[chevyrestore]

Hey guys I took another drive today and figured something else out also. I took the air cleaner off and ran the motor with the carb exposed just down the block for testing and it was a TON better, still had a very slight stumble feel and hesitation but it was almost completely gone.

That makes me think its probably all in the carb, with the symptoms I described do you think I should try to lean or enrich it to make it better? or just rebuild? thanks for all your help and suggestions.

[chevyrestore]

Ok guys I think I may have pinpointed the problem. I tested the brake booster for a leak and the vacuum line going to it. All good there.

I sprayed the top of the motor with brake cleaner and found that it would stumble/shake more when spraying the cleaner around the passenger side of the carb.

I replaced the base gasket and that helped a little.

I resprayed the area and found that an addition stumble area happened when I sprayed it around the manual choke linkage points on the passenger side of the carb.

Would a leak small enough around the linkage area be enough to cause that stumble under acceleration? Im starting to think it may be an accelerator pump as well. Any good ways to check that on the car? I see the mains spraying but I dont know how hard it should be.