440 will not idle

[chargerrtmikey]

I have a 69 charger with a 67 440 I don't know anything about the internals of the motor other than it has a BIG cam in it. The problem with it is that it will not run on the idle circuit the rich/ lean adjustment screws have no effect. I have tried 3 different carbs a 750 edelbrock, 750 holley and now it has a holley 750 double pumper. Is the only answer is to swap cams?

[b5blue]

First check ignition settings, where are they set to. Also look for vacuum leaks as that can kill idle. Large cams idle lumpy. Post pics. 

[chargerrtmikey]

There are no vacuum leaks, timing has been set just about everywhere but no effect the idle has been set as low as possible

[b5blue]

Your not giving much to work with.

[BSB67]

There are no vacuum leaks....

You know this how?

[chargerrtmikey]

I replaced all vacuum lines, sprayed carb cleaner around potential leaks but nothing the engine runs strong just will not idle on the idle circuit maybe not enough vacuum?

[myk]

Disconnect the headlight vacuum system and cap it off at the booster; there could be a leak there too.  I ran with a vacuum leak there for YEARS and never knew about it...

[ws23rt]

A vacuum check with a gauge at the carb will tell the best story.  If you do have good vacuum but it still won't suck than the idle circuit in the carb may be clogged

[billschroeder5842]

When you say "it won't idle" do you mean it won't run at all? If it does run, how low of an idle can you go before it dies?

[cudaken]

When you say "it won't idle" do you mean it won't run at all? If it does run, how low of an idle can you go before it dies?

I was going to ask that my self.

Mike, what do you have the timing sat at? Do you have a Mechanical or Vacuum Advances distributor? 

I have a fairly big cam, MP Purple shaft 292/292/509/509 cam and bottom end was Chevy and lumpier than heck. (would idle) Had the engine at stock timing mark, then I advances it to 14 degrees BTDC and it was a little better. I now have it sat at apx 20 degrees BTDC and engine is smoother and bottom end is much crisper.

Here is what I suggest. Discount all vacuum lines. Get a vacuum gauge and advances the timing till you have the highest vacuum reading. Then see how she idles and take her for a test drive. If she knocks, retard the timing 1 degree and test drive again.

With you trying 3 different Carb's I don't think all 3 would have a bad idle circuit.

On you not having a vacuum link? One thing I have learned. Just because it cannot be the problem does not mean it is not the problem! 

Cuda Ken

[chargerrtmikey]

I have done the vacuum gauge and the most vacuum I can achieve is 8 to 9 on the gauge and that is at 14 degrees advanced. The 3 different carbs are all new. The engine will idle but the adjustment screws have no effect you can turn them all the way in and the engine RPM is the same. I believe it is bypassing the idle circuit due to low vacuum that the big cam is producing

[firefighter3931]

I have done the vacuum gauge and the most vacuum I can achieve is 8 to 9 on the gauge and that is at 14 degrees advanced. The 3 different carbs are all new. The engine will idle but the adjustment screws have no effect you can turn them all the way in and the engine RPM is the same. I believe it is bypassing the idle circuit due to low vacuum that the big cam is producing

If the idle circuit is unresponsive you have the idle speed adjustment screw set too high and it's running on the main circuit....not the idle circuit.  

With a big cam profile the engine is going to want lots of base timing. Try advancing the base timing using a vacuum guage. Adjust for max vacuum then readjust the idle speed. This might require a re-curve on the distributor mechanical advance mechanism but for now just focus on getting the idle circuit functional.

In some cases you have to drill small holes in the primary throttle blades to allow more air into the venturies.

Is your holley 750dp a 4 corner idle carb ?



Ron

[chargerrtmikey]

It is a 4 corner idle carb. I have advanced the timing and got the max vacuum per vacuum gauge and adjusted idle speed as low as possible but still running on the main circuit

[firefighter3931]

It is a 4 corner idle carb. I have advanced the timing and got the max vacuum per vacuum gauge and adjusted idle speed as low as possible but still running on the main circuit

Are the secondary throttle blades fully closed ? If so you should try cracking them open a bit to see if that helps. 

It definately needs more air at idle than it's getting. In the past i've drilled 1/8 holes in the primary throttle blades to allow extra air into the venturies. This allows you to close the throttle adjustment enough to get it to idle on the idle circuit. If too much (or all) of the transistion slot is exposed you'll never get the idle circuit functional. 


Ron

[chargerrtmikey]

Thanks Ron ill give that a try