70 302 starts, but won't idle :(

[anothersmith84]

I've got a 1970 coupe with a 302, Edelbrock 1405 carb, Edelbrock performer intake, hooker headers and stock points/condenser system.

I bought it running a few months ago, but it wasn't running great. It ran rich and at a high idle. It would die when I first put it in gear, unless I took off quickly and drove it around for about 10 minutes, then it would be fine. It also had less power than expected.

I replaced:
-Distributor Cap
-Rotor
-Spark plug wires
-Spark plugs (with copper plugs all gapped to .035)
-fuel filter
-Vacuum lines running from the vacuum advance to the carb, and lines running off the intake manifold

After that, it ran slightly better but still not great. I tried to adjust the carb, but the idle mixture screws did nothing to the idle and if I lowered the idle below ~3K RPM, it would die.

Next, I rebuilt the carb. I changed all the settings back to stock including the idle and idle mixture screws which are now at 1 3/4 turns out.

Today's the big day of the first startup after the rebuild and the engine won't run for long. It starts right up if I hold my foot into the pedal. The engine runs at 3000 RPM and sounds smooth if I rev it higher. As soon as I try to let off the gas, the engine will die. No idle at all.

There's also a new noise. Before it dies, at around 2000 RPM, there is a whining noise. Its not a squeak like a belt makes, but a whine that goes with the engine speed. It will be higher and quieter at higher RPMs, but louder and slightly lower pitched at lower RPMs.

Any ideas?

 

[woodsnake]

Somewhere you have a vacuum leak I'll bet. Bad gasket, cracked hose, somewhere.

 

[anothersmith84]

What method would you suggest to find the vacuum leaks?

I've heard that I can disconnect one line at a time and cap it off, then start the car and see how it runs. But then I thought running the car without vacuum advance might damage the engine or cause other problems..

 

[Fstbk]

What method would you suggest to find the vacuum leaks?

I've heard that I can disconnect one line at a time and cap it off, then start the car and see how it runs. But then I thought running the car without vacuum advance might damage the engine or cause other problems..

I have used a small butane torch (un-lit of course) while the car is running, if the RPM shoots up while passing the torch over the various parts of the motor thats your leak.

We use this method on the old V-twins a lot because it makes less mess than starting fluid.

 

[Rusty67]

I second the vac leak issue. Does it have a carb spacer plate ? Check to make sure the gaskets are good there. Also check your intake to head gaskets. You could have a hanging vac line open somewhere thats just sucking in all over the place. Do you have an auto trans ? Check the line that comes off the intake to the trans tube.

I was going to suggest carb cleaner or brake clean but using an unlit torch... that is an original one. I'll have to try that the next time I am hunting for a vac leak (hopefully not soon).

 

[anothersmith84]

Update time!

I tried the carb cleaner method, but I didn't notice any change in idle when I sprayed around the carb and lines.

I do have a carb spacer that I didn't replace, so I figured it would be a good idea to check that gasket visually. The gasket looked fine, with no evidence of leaking. The spacer was cracked, but only on the inside (pic). I replaced the gasket and the spacer.

I tried it again and got the same thing... no idle below 3K RPM or so.

So I decided to try to cap off the lines going to the transmission and brakes just to see what would happen. No change in the idle. Although I did notice a potential vacuum leak with the vacuum advance, the nipple (hehe) came out and is now stuck in the vacuum hose. (pic).

So what am I missing? Assuming I replaced everything correctly what else could be causing my vacuum leak?

 

[NMEMJCM]

did you shoot some of your carb cleaner on all sides of the intake manifold? Thats definately an area for a possible leak. check there. And for shats sake..... get your nipple squared away.... just sayen.

 

[scarb1174]

Just had the same problem with my 66 289. It was the points, they were out of adjustment. I cleaned the contacts with emery cloth and then reset them to .016.

 

[HDTony]

Unless I missed it you make no mention of your timing? Have you checked it? Since you stated you rebuilt the engine I'm assuming the distributor was out of the motor. Check your points, check your timing, are the wires cap and rotor new? Are you sure the distributor isn't off a tooth. Considering, your having a similar problem from before the rebuild I'm guessing it distributor or carb related, swap a new one in and see what happens