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52' 300 timing / vacuum advance
Just popping in
Just popping in

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Its been a while since I last posted due to life getting in the way. I am getting back to working on my 52' 300 trying to get it ready to enjoy this summer.

It all started when I had issues with the accelerator pump in the carb not working and not allowing me to accelerate. So I ordered a rebuild kit from Max Merritt and rebuilt the carb. Got everything put back together and got the car fired up with using the base fuel screw settings of 2 turns out. It was idling higher than I would have liked, so using a dwell/ tach meter, I am able to watch the RPM and dwell with the car running. Currently the Dwell is set to 24 degrees which is within the spec of 21-30 degrees according to the service manuals. These measurements are taken with the Vac Adv disconnected at the carb and the carb plugged off. I cannot get the idle down to the factory spec of 450-500 rpm without the car dying. Currently its idling around 750-800 RPM with the Vac Adv connected, but has an audible miss at idle. It smooths out when given throttle.

I thought that the timing may be off since it won't idle at the correct RPM. After checking the timing with a timing light and Vac Adv disconnected. It is right on at 6 degrees BTDC which I believe to be within spec. When I check the timing with the Vac Adv connected, the timing jumps up to 16-17 degrees BTDC and continues to advance further when RPM's are increased. It has the Delco distributor if that matters.

My questions to the experts:
1. Is the timing supposed to be set to 6 degrees with the Vac Adv connected?
2. Is my advance of 16-17 degrees with the Vac Adv connected seem reasonable. Is this due to the RPM's being elevated above the normal spec of 450-500 RPM?
3. I assume if I can get the RPM to 450-500 then there shouldn't be any timing advancement from the Vac Adv? If its still advancing at 450-500 RPM is there any adjustment to the vacuum canister to reduce the advancement or does it need rebuilt?
4. Any other suggestions or areas to look at?

thank you for any insight or help you all can provide.

Posted on: 5/21 23:03
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Re: 52' 300 timing / vacuum advance
Home away from home
Home away from home

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You will need to set your base timing with the idle down in the 400-450 range. Otherwise, the centrifugal advance inside the distributor begins to kick in and you will get a false reading. I just had in a 52 with the idle set way high. When I got that cranked down it turned out the timing was about 8 degrees retarded which explained the overheating and poopy performance.

At low idle the carb is so constructed that the vac advance receives no vacuum and thus does nothing. I usually don't bother to disconnect them when checking timing --I just make certain the idle is good and slow--and there is no need at all to plug anything.

A short observation will show if everything is basically correct: while using your timing light slowly give gas. In very short order, the vac advance will kick in and the timing will jump. Give more gas and the timing will slowly increase with speed as the centrifugal advance does its job. Then snap the throttle shut and the timing will instantly jump way back as the vac advance goes out of the picture. Then as the engine slows to an idle the timing will return to base.

Posted on: 5/22 6:24
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