[89WhiteGTRagtop]

I've got a Holley 600 with vaccum secondaries on my 66 stang that has a 302 in it. It has ran fine for about 5 years....until yesterday. My car started "missing" at high rpm, and at idle it's missing so bad, the motor is shaking violently. I'm assuming it's a fuel problem.

Here's what I've done:
1) Checked the fuel filter...it's fine.
2) Checked the float levels, and the front bowl was full to the top. So, I took off the front bowl, checked the needle and seat, reset the float level and put it back on. It was still filling to the top, so I removed and reset the rear float level too. The fuel level seems to be fine now in the front and rear bowls.
3) I put new plugs in it because I thought since it was running rich that I had fouled a couple of them. The plugs looked fine, but I replaced them anyways.
4) I am getting spark to all 8 cylinders.

I have a Mallory Unilite distributor as well. I bumped up the idle on the carb and it will idle a little better, but when I tach it up it starts popping out of the exhaust and it feels like it's only running on 5 or 6 cylinders.

WTF is wrong????? Anyone? This carb was bought brand new 5 years ago and has only about 1500 miles on it. Thanks.

 

[TommyN]

I may not be much help, but why are you assuming carb instead of ignition? It may be helpful to follow a troubleshooting check list to narrow the problem. Maybe a bad wire, cap, rotor, or coil? If it is carb related, maybe the power valve is blown. This should only affect the idle or part throttle. WOT should be OK. The plugs would be fouled if you had a blown pv and you could see the gas pouring into the carb at idle if you looked at the boosters. A stuck float would cause flooding at idle as well. Good luck! Tom

 

[SinisterSnake]

Check your fuel pressure, my car was doing that last year, come to find out i only had 4psi.

 

[89WhiteGTRagtop]

Tommy: I am pretty sure it's not ignition because I have spark to each plug even while it is running like crap.

How do I check my fuel pressure? I've done it on my 5.0 through the schrader valve, but what about on a carbed car?

 

[stangPlus2Birds]

What's a carb?

Does it sound like a miss or stumble? Can you see the gas going into the engine? Does it look like a fine spray or blobs? Does the engine Every smooth out? Get a sight plug for the side filler hole. They are good for the first few months. After that, they get cloudy.

Get some starter fluid. Do you have an open element air filter. If so, it's harder to check for vacuum leaks. Use the starter fluid to check for leaks. Check your vacuum.

You can get 4 bls super cheap at swap meets. 2 years ago, I threw out over a dozen carbs. I used to swap carbs at once a year.

 

[CP85GT]

A vacuum leak from the carburator itself might cause the symtoms you mentioned. At idle a bad carb vacuum leak will cause a lean condition causing the carb to try and compensate and dump gas through the boosters I think, I had a 600 dp holley that did this until I jetted up. This could be why your plugs are fouling. At high RPM you would get a miss and detonation from a lean condition. Your holley should have several vacuum ports on it. Check to make sure these are all sealed. Check to make sure your carb gasket is still sealing, and that your carb base plate is not cracked(holleys do this) Another thing to check is for a bad coil even though you don't think it is ignition related. I had a coil go bad which caused the engine to idle poorly, run rich, and miss. These are just some things that occur over time and have happened to me so I hope the info helps.
Eric