panchop

couple things.
the engine is a 327 with with a edelbrock RPM cam, heads, and airgap manifold. running about 10.5 to 1 compresion. using stock distributor and points.
1) when i tighten down my distriputer clamp the last couple turn it will change my timing by a couple degrees?
2) my engine returns to idle slowly and i am only making about 8 psi of vacume at 800 RPM. i suspect a manifold leak but is there a good way to check?
thanks
greg

johnfharding

The most common procedure I have heard is to take a can of WD-40 ,,, or Carb Cleaner and spray intake to head seal areas with the substance while the car is idling, while you are doing this and listen for a change in idle speed up or down,,, if you use carb cleaner be careful of painted areas,, as I have seen this stuff remove paint. I don't know about the distributor,, try setting it two degrees advanced of what you want it and tighten. or have some one hold it while you tighten it..

INMYBLOOD

Sounds like your gonna figgure it out alone..!!! I've used spray start .... I think. You get a speed change when you find the leak. My hold down clamp has given me fits through the years. Not a vacuum leak just loosens and weeps oil.

67L36Driver

Find a large flat washer that will fit around the dist shank after you saw it in half. Put it under each leg of the hold down clamp. Dist housing surface is dug up from years of use and the clamp is finding its old 'home'.

DansYellow66

I've noticed this on nearly every car I've owned with a distributor. I think it has to do with some tolerances in the dist housing to block fit that a running engine moves in one direction from the cam/distributor gear loads, and then when the clamp is tightened it moves it back to centered, slightly changing the timing. Same thing happens on my Plymouth. I just learn to use a little windage and compensate so that it ends up where I want it with the clamp tight.

Assuming you don't have a pretty radical cam the 8 deg is really low. What initial timing are you setting it at? Is this manifold vacuum or off the carb? I think I've also heard of using a propane torch (unlighted) to check along the intake manifold to block surface - the RPM will increase if you hit a vacuum leak. Of course the leak could be to the interior of the engine which is more difficult to check.

66BlkBB

1) when i tighten down my distriputer clamp the last couple turn it will change my timing by a couple degrees?

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One other thought. If you are using a fiber washer under the distributor flange it could be that it is saturated or spongy and when you tighten the distributor down the washer collapses and allows the distributor to move downward changing the timing by a couple of degrees when the gears push deeper into the cam gear. Not sure how you could cure it other than putting in a non-porous washer, if you use one.

California Cowgirl

We have the same problem on our 61, but no matter how tight I hold it it still looses 2 degrees when I tighten it down...Tried to advance it 2 deg. figuring it would work..Nope..so right now it is still off by 2. Where do you get internal vacumn leaks???? New manifold, new carb and still have a problem...I am no expert and just need some input from the forum..it must be something I am missing...will try the "washer fix" on the distributor. THANKS!

MikeM

If you're using the spring steel hold down clamp, I'd exchange it for one of the flat, stamped steel clamps. I think your problem will go away then.

DansYellow66

[QUOTE= Where do you get internal vacumn leaks???? THANKS! [/QUOTE]
Instead of the intake gasket leaking to the exterior of the engine, it can also leak on the bottom side to the interior of the engine, into the lifter valley. Depending on the condition of the engine the lifter valley may be slightly pressurized or it may be very slightly negative from the PVC system. Either way 15 inches of vacuum at idle will overcome it and pull air from there if the gasket isn't tight.

California Cowgirl

Thanks for the response Dan, but we only have 10.5 " of vacuum at the intake manifold...Could the problem be a single plane high rise aluminum intake manifold (which I understand will lower vacuum) Could Dart heads contribute???? We have an older Mallory distributor, that has very little use, but we do have the problem in tightening it down...will try the washer trick...Thanks for all of your help Forum members!!!

panchop

vacume leak turned out to be a bad/wrong type gasket on the power brake booster end of the connecting hose between the manifold and brake. pulled my distributor. found about .058 of end play. don't know if that is the culprit. i will also change to a solid type hold down clamp as i do have the spring type.
thanks
greg