440 not running right

[barryv]

hi, i have a 72 440 in a barracuda that seems to have a miss and idle seems to go up and down. i have performed tune up etc. any tips.thanks

[FJ5_440]

Since it has had a recent tune up, I would look for a vacuum leak first.

[MEK-Dangerfield]

It could be a number of things. If not a vacuum leak, what kind of shape is your carb in? Is it new, or newly rebuilt and set up correctly? The problem could be electrical too. One of the spark plug wires might have a crack in it, and it is arching to ground. If the plug wires are new, make sure they are on all the way on both the plugs, and distributor. One of my wires going to the distributor wasn't quite on all the way, boy was that perplexing.   


  Mike

[71chally416]

BB Mopes are notorius for cooking plug wires. That would be suspect #1 to me. Make sure none of them are laying on the exhaust.

[barryv]

plug wires have been changed,i took another carb that belongs on my roadrunner and it still runs bad.i even ran gas straight from a gas can and it didnt help.im going to look for a vacum leak again.any other ideas would be appreciated,thanks

[MEK-Dangerfield]

Is it missing at idle, while at speed, or both?

[barryv]

this is going to sound strange but only at idle.it doesnt have a tranny in it yet but i have bellhousing on it so i could mount starter. it used to run smooth but now it seems to miss and idle surges up and down.it starts right  up so i think timing is close although i dont have a timing gun.new timing chain was installed last year

[MEK-Dangerfield]

this is going to sound strange but only at idle.it doesnt have a tranny in it yet but i have bellhousing on it so i could mount starter. it used to run smooth but now it seems to miss and idle surges up and down.it starts right  up so i think timing is close although i dont have a timing gun.new timing chain was installed last year

When I had my problem of one of the spark plug wires not pushed down far enough into the distributor cap, it would only miss at idle...That's why I asked. In fact, the engine would almost stop/freeze sometimes when it missed. If I pushed on the gas, no miss. I don't understand the surging though.     That sounds like a vacuum leak that is sometimes there. Under the carb is where I've had leaks in the past, so I apply Gasgasinch on the gasket now to prevent that. Have you replaced the valley pan gasket recently? That would be my second guess for a leak.

[Grancoupe]

I posted this nce before. Wait till it gets dark and run the engine to where the miss starts to happen. Closw the hood until you can just see into the engine compartment and look for a light show. Easy way to see if your wires are arching. I would do some searching through the past threads as this whole thread is a repeat.

[barryv]

i  ran it at night no arching.can it be anything internal. i did not change manifold or anything . iam going to check for vacum leak next weekend,thanks

[Grancoupe]

Got a vacume gauge on the motor. Should be pretty steady. If there is a fluctuation then it could be mechanical.

[barryv]

no, i dont have a vacum guage.are they expensive

[Chryco Psycho]

not very , probably pick one up for under $20 at a discount tool store

[Grancoupe]

If the car has been sitting and just started a miss in the engine I would go after plugs first. Doesn't hurt to check you cap and rotor. Had a cap and rotor cause a few cylinders go south but that was while I was running the car hard.

[barryv]

all tune up parts were replaced. ill try to check for vacum leak again