Re: IML: 73 now runs..(but)

[David Whitney <hazegreen66@xxxxxxxxx>]

Jerry, you need to warm up the engine before setting the timing.  Also, make sure your ignition and carburetion is in top shape.  No vacuum leaks, no electrical interference and no dirty connections.  I recommend the "total timing" method.

 

Running the same gas you normally do (no additives, unless you always use them), make sure the engine is good and hot.  Disconnect and plug the vacuum advance port at the carb.  Connect a vacuum gauge to the carb's other front port -- that's manifold vacuum.

 

Loosen the distributor hold down clamp and twist the distributor cap until you have the highest vacuum reading.  Tighten the clamp.  Whatever the timing mark says at this point is the initial advance your engine combo likes best.

 

Have a buddy, wife, whatever help you do this while you watch the timing mark.  Raise RPMs to 2500.  Your car probably does not have a tachometer, so have the helper press on the accelerator pedal or pull on the carb accelerator linkage until the timing mark does not advance any further.  Now your mechanical advance is "all in".

 

You do not want more than 36 degrees total advance.  Mechanical advance from the distributor is fixed, so if "all in" is above that, retard initial advance by the appropriate number of degrees.  If your damper does not have a timing tape or marks indicating every ten degrees, you'll have to scratch some in.

 

Disconnect the vacuum gauge and cap the manifold vacuum port.  DO NOT connect vacuum advance yet.

 

Now take it out for wide open throttle acceleration.  Wide open.  Mash that puppy to the floor.  If it pings, retard initial advance some more.  If you have to retard initial advance to the point where idle is poor, you have the wrong distributor advance curve and you need to have that changed.

 

Once you are satisfied with your initial advance, plug in the vacuum advance.  Now, here is where most people miss the boat.  Wide open throttle means zero vacuum advance.  You are testing nothing at WOT acceleration.  Do a series of part throttle accelerations.  Your hill sounds like a good place.

 

Remember, at this point your initial and mechanical advance are where you want them.  If vacuum advance is too high, you can adjust it using an Allen wrench at the diaphragm.  A small change has a great effect.  If your diaphragm does not have this feature, get one that does.

 

If your acceleration is just fine but the car goes BLAP BLAP BLAP when you let off the gas, here's what's happening:  You are at full initial and mechanical advance at 2500 RPMs.  When you let off the accelerator pedal, you have dramatically increased manifold vacuum, and your vacuum advance is "all in".  To correct this, you must retard the vacuum advance.

 

Some big block Mopar engines like absolutely no vacuum advance.  I have a 383 in a "lesser" Mopar that is that way.

 

Once you have set timing correctly, the next thing to look at with part throttle acceleration is your carb jetting and metering rods.  A lean condition will also result in a ping and possibly a backfire if it's bad enough.  But that's a topic for another day.

 

Happy motoring,

David

'91 K-Imperial driver
'66 Crown Coupe project
'66 LeBaron dual air and every option known to man

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