Low vacuum on stock 383

[Yellow Submarine]

Just went back into the garage and tried the #7 that was only 100psi. I tightened up the fitting and got 110psi consistently. That's a bit closer to the others but still low. I'll try to improve the idle a bit or try another carb and drive it an see if that helps.
If all else fails there's always a 440 or Hemi. Ok maybe not a Hemi.

John

[Strawdawg]

I would be tempted to do a leak down test and if it is okay, I would change the cam to something known to work with factory stock components


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[Yellow Submarine]

Ok since the last time, I went back to all the cylinders doing another comp check. I was more careful to be sure the screw in connector was tight. I also propped open the throttle blades as I had overlooked this previously. The max compression came back at 120psi +\-about 5-6 psi. So now it's still low but at least somewhat consistant.
I cleaned and gapped the plugs, checked the wires for high or inconsistant resistance. I took an old (but not worn) Holley, put a rebuild kit in it and replaced the Carter and fired it up. It runs basically the same as it did prior to these changes.
It's looking like I need to check the came indexing and maybe change out the cam to a known quantity. I'll let you know how this goes and thanks for all your help.

John

[Yellow Submarine]

This afternoon I found a stand alone tach to see the RPM and went about adjusting the idle on the carb. I placed the vac gauge inline and kept lowering the idle speed then adjusted the two idle mix screws to even it back out. I kept going back and forth until I got it to about 850RPM and maintained 17.5MMHG vac. It idles better than it has before and the throttle response is crisp. I can put it in gear without stalling it. I will try putting a few miles on it and re-check.

John

[734406pk]

I would be tempted to do a leak down test and if it is okay, I would change the cam to something known to work with factory stock components


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  I would do a leak down test on this engine to find out if there is a compression leakage issue here. If no leakage problem is found, your cam timing may be set up late. This would explain the 120 psi compression pressures you are getting. The leak down testers are fairly economical. Summit has them for around $50 or so.

[Yellow Submarine]

Thanks again Andy