The Stovebolt Site Forums The Shop Area Engine Shop How MUCH Vaccuum should I have??!!

Now That my old 235 in the 61 Apache is running, I'm trying to debug the thing. It idles fine, but when trying to give it a little juice it will stumble and misfire badly. The Vaccuum advance does not seem to be working. Put the gauge to it and I have a steady 10" at the end of the vac line in front of the advance, and also checked with the same steady 10" result at the port on the carburetor, so it seems to rule out any restriction in the line. Is 10" what should be there? Is that enough to operate the advance? Putting the gauge to the vac port on the side of the intake I get a rapidly fluctuating read between 19" and 20". When I SLOWLY give it a little throttle, the vacuum at the intake rapidly descends to a wildly fluctuating 12" to 15". Loosened the bolt behind distributor and manually advanced while idling, Vac went to a 20" to 21" reading for several seconds and then leveled back to the 19" to 20" read again. It seems like a exhaust restriction, but the entire system is new, except the manifold itself which was bead blasted and boiled out, new spring on the counterweight, etc, etc. There is a small leak at the counterweight, evidenced by black soot. I've been told that something like a sticky or burnt valve would cause a larger and slower fluctuation than just 1" of vac while idling.Sorry to be so long winded, just trying to let you all know what I've covered, and hope the gurus that have gone before me can tell me what I'm missing. Thanks in advance, Tony

a regular ticking fluctuation on the vaccum gauge could mean just that the valves need to be adjusted. Might start with that. I.E. one valve is not closing all the way. A quick check with compression testor might show which cylinder.

I am assuming that you have the timing set to to stock and the motor is stock.

You can check the vaccum advance on the distributor by putting a vaccum pump on it and then watching the timing light.

Well, while I thought to check vacuum at the line, I did neglect to check the advance can itself. It is toast. I checked one on a spare distributor I have lying on the bench and that one is good. I'll swap that out in the next day or two, and go back to the beginning, recheck the timing, dwell, and re- re adjust the valves. I'll get hold of a compression gauge and check that as well, havent as of yet. Then I'll throw a new set of plugs in for good measure, and see where I'm at. I decided to get the pertronix as well, should be in by end of week. Looks like I'll be busy next weekend. Thanks for the input gentlemen. Tony