stored 1969 runs, but won't idle

[Map]

We are working on a 1969 429 that will start (after adding a new carburetor, new points and new condenser) but will only run a high (3000+) rpm. The car had been setting for an unknown period of time and we were told it needed a carburetor. Backing off on the throttle results in the engine dying. There is fuel to the carb and the spark seems good. We'd like to get some ideas on where to look for the problem.

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[OneAmongOthers]

Some possible issues for irregular running engine/idle, and my god 3000 is a very high idle for a big block!

1: Engine timing is off.

2: Check the vacuum advance can on the distributor.

3: Distributor itself is bad and needs to be replaced.

4: Improper fuel/air mixture.

5: Timing chain is stretched.

6: Throttle cable connected to carburetor is incorrectly set and or damaged.

7: Internal engine issues.

 

[64ZCODE]

Sounds like air leak of some kind. You could block off all the vacuum lines at the source (carb, manifold) and see if it idles then. Obviously don't try driving the car as you won't have power brakes. If it idles, then try reconnecting the vacuum lines one by one until you find the culprit.

 

[Map]

Sounds like air leak of some kind. You could block off all the vacuum lines at the source (carb, manifold) and see if it idles then. Obviously don't try driving the car as you won't have power brakes. If it idles, then try reconnecting the vacuum lines one by one until you find the culprit.

Thanks. since replacing the points and condenser did not affect a change, vacuum seems to be a good guess. I'll post after we have a chance to check this.

 

[05Dave]

We are working on a 1969 429 that will start (after adding a new carburetor, new points and new condenser) but will only run a high (3000+) rpm. The car had been setting for an unknown period of time and we were told it needed a carburetor. Backing off on the throttle results in the engine dying. There is fuel to the carb and the spark seems good. We'd like to get some ideas on where to look for the problem.

Had the same problem with a 67 Corvette tri-power set up. In my case the guy who rebuilt the carbs put the same gasket in each carb. The center carb has a different gasket because it has a primary circuit. I would check that you have gas coming out of the primary jets. Sounds like you don't have a fuel supply at idle. Biggest issue will be losing the bottom end as rod bearings do not like to be revved when cold.

 

[05Dave]

The vacuum leak is also a good choice, but it would a severe leak. I had a similar leak on a Chev p/u small block. Leak was in the PCV line and the previous owner had just cranked up the idle and opened the air control screws to counter it. The idle was limited to about 1500 rpm before it smoothed out.
All old hoses should be replaced, but still do a individual hose check if that doesn't work. Sometimes it is what the hose us connected to that has failed.

 

[64ZCODE]

I was thinking PCV as well, possibly the valve itself is defuctive. Fortunately these cars are pre-EGR valves so we can rule that out!

 

[05Dave]

Just remove the hoses one at a time and plug with your thump or a suitable push cap. Do not plug with something too small or the engine could digest it. Check the primary idle circuit on the carb too.

 

[05Dave]

Make sure the air screws are set to specs. Not sure what that should be but possibly one full turn open and adjust from there once you establish a reasonable idle. But do not jas the throttle much. That cost me a crank and bearing set.

 

[05Dave]

Look at or run your fingers around the carb base. Is it possible the carb was designed for a pcv and the hole is open? Usually in the rear or front of the throttle base