Flathead low intake vacuum

[oliverguy]

I’m working on a 46 ford flat bed truck. It has 78k miles on it and it has not been on the road since 1976. I have very low intake vacuum, only 6” at the wiper port. All cylinders have 50 psi of compression. I’ve found some leaks and also changed the intake manifold gasket because some bolts were loosened to replace the spark plug wires.

Cranking the engine over I watched the valve lifters
And all of them are Moving. I put some oil down each spark plug hole. What would be causing these low readings? I have nice hot spark and plenty of fuel. I can’t even get it to cough at all. I timed the
Distributor on the bench, could the timing be off enough to not have it
Even try to fire?

[Ggmac]

Kinda low on the compression. But it should at least ignite . Is your firing order correct. #1 on passenger front . Blocked exhaust ? Fresh fuel with a good carb , plugs gapped correctly.
You have good spark at the plugs so Im thinking fuel or ignition timing . The distributor can only go on one way , unless you force and crack it .
Coffee is calling , Ill keep thinking but will need more info . Others will chime in that are far better than I .
Gary

[Terry,OH]

See chart below. Looks like a vacuum leak. Yes it will make the engine hard to start. If you are unable to get the car running you can't do a vacuum test. The test is to be done at idle with the engine warm.

[petehoovie]

Originally Posted by Terry,OH

See chart below. Looks like a vacuum leak. Yes it will make the engine hard to start. If you are unable to get the car running you can't do a vacuum test. The test is to be done at idle with the engine warm.

[drolston]

Try a squirt of starting fluid (ether) in the carb while cranking. If the engine fires on that it should keep running on gas. If you get it running, drizzle some MMO in the carb while jazzing the throttle to keep it going. Run it up and down for 20 minutes or so. Then run your compression check again. It could be considerably better. Remember to leave all of the plugs removed and block the throttle full open to get the truest reading.

[slowforty]

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I got 15 in vacuum on my old motor. It had 60lbs compression on 7 cyl and 35 on one. Ran decent for a long time.

[rockfla]

Originally Posted by Terry,OH

See chart below. Looks like a vacuum leak. Yes it will make the engine hard to start. If you are unable to get the car running you can't do a vacuum test. The test is to be done at idle with the engine warm.

Terry, even though Pete enlarged the file here on the barn I sure would like to get a cleaner copy of that chart you posted.....Might you be able to email it to me to see IF it comes across any crisper and cleaner.....I love to put that up on the wall of my shop!!!! [email protected]

[cadillac512]

If the vacuum is being checked while cranking (won't start so it's not running) it'll be low for sure, and will drop to zero when holding the throttle open. That won't cause it to not start. A shot of starting fluid is a good idea since that rules out the fuel system.

You can check timing with a timing light while cranking if you want to verify timing. Use a 12v battery to power the timing light if necessary.

[panic]

Is the spark @ full retard?
Try advancing it a bit.

[oliverguy]

Thanks for the suggestions. I’m going to try timing adjustment and make sure there isn’t anything stuck in the exhaust

[alanwoodieman]

V8 or I6? sounds like stuck rings, I am working on a 49 truck that has sat for 18 years, soaked the pistons/rings with ATF and acetone, when I let this mixture sit for 10 days in the engine compression started coming up, when cold it has 110 to 120 lbs compression. running it has 18/20 vacuum with a slight fluxation so started pouring mmo down the carb and added some to gas valve finally freed up and sounds good. timing is set with the distributor off the engine but look on ps side for a screw with a plated--loosen scre and move plated up one line at a time