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Old 11-03-2020, 12:45 PM   #1
hmmech
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Default engine vacuum problems

i have a rebuilt 53 ford flathead engine ,ever sense i 1st started it ,it starts right up but rough idle and vacuum gauge jumps all over from 5-12"and increase rpm from 8-15"with little pops out pass. side of exh., i did a compression and cyl. leak down test looks ok, the vacuum chart shows could be leaking head gasket, put new head gasket in and the same thing, i do have new alum heads which look ok, could they be warped and causing this problem, also checked my 2x2 intake manifold and carbs with no leaks, not sure where to look now. any help out there ?
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Old 11-03-2020, 12:51 PM   #2
big job
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Default Re: engine vacuum problems

sounds like tight valve lash from here....
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Old 11-03-2020, 12:58 PM   #3
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Default Re: engine vacuum problems

First I'd make sure there aren't two plug wires switched. Then I'd idle the engine and short each plug wire in succession to see if each drops rpm slightly as it's shorted. If you can isolate the affected cyls it will be easier to diagnose.



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Old 11-03-2020, 01:19 PM   #4
hmmech
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Default Re: engine vacuum problems

readjusted already
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Old 11-03-2020, 01:31 PM   #5
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Default Re: engine vacuum problems

Sounds like a vacuum leak to me.
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Old 11-03-2020, 01:40 PM   #6
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Default Re: engine vacuum problems

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Sticking valves perhaps--- try some oil--- memo--
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Old 11-03-2020, 01:42 PM   #7
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Default Re: engine vacuum problems

Any kind of head gasket or warped head issues would have shown up on the leak-down test. I'm with tubman, sounds like a vacuum leak somewhere.
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Old 11-03-2020, 01:50 PM   #8
1931 flamingo
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Default Re: engine vacuum problems

Vacuum wipers??
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Old 11-03-2020, 01:55 PM   #9
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Default Re: engine vacuum problems

I'm with others here re vacuum leak. As a possible point of reference, best my '47 with 30,000 m will do at running temp is a steady 19.
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Old 11-03-2020, 04:26 PM   #10
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Default Re: engine vacuum problems

Try spraying brake parts cleaner around base of manifold,carb,anyplace where you could think of where it would leak. The rpm will change when you get close. Wiper hose is another possibility, mine was all cracked, I found it when I tried to lube the wiper motor with a syringe and I had a puddle of MMO under the dash.
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Old 11-03-2020, 04:51 PM   #11
hmmech
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Default Re: engine vacuum problems

my 53 has no vacuum wipers so i will try spraying around the intake and check for leaks
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Old 11-03-2020, 05:03 PM   #12
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Default Re: engine vacuum problems

Quote:
Originally Posted by hmmech View Post
readjusted already
How did you go about adjusting the lifter clearance?
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Old 11-03-2020, 07:46 PM   #13
hmmech
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Default Re: engine vacuum problems

I went by the book to adj the lifters,had holes drilled in the housing to hold the lifter in place while adjusting and they were tight locked in place
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Old 11-03-2020, 08:51 PM   #14
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Default Re: engine vacuum problems

Which book, LOL?
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Old 11-04-2020, 11:20 AM   #15
hmmech
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Default Re: engine vacuum problems

How to Rebuild and modify ford flathead v8 engines. maybe i should have read it twice.
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Old 11-04-2020, 11:43 AM   #16
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Default Re: engine vacuum problems

If valves adjusted correctly. I'd guess its the valves sticking with tight new guides. mmo down the carb till it smokes out and then drive it. Repeat.
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Old 11-04-2020, 11:46 AM   #17
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Default Re: engine vacuum problems

I would think a vacuum leak in the intake would just create a consistent low vacuum reading through out. Not a erratic vacuum reading, that would show a individual cylinder or valve issue.
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Old 11-04-2020, 06:41 PM   #18
hmmech
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Default Re: engine vacuum problems

i will try mmo tomorrow, i put a little in the oil and gas tank ,but didn't do the carb
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Old 11-04-2020, 06:53 PM   #19
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Default Re: engine vacuum problems

Just going to ask what cam, so we can judge roughly what vacuum it should be.
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Last edited by Talkwrench; 11-05-2020 at 12:58 AM.
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Old 11-04-2020, 07:32 PM   #20
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Default Re: engine vacuum problems

Quote:
Originally Posted by hmmech View Post
How to Rebuild and modify ford flathead v8 engines. maybe i should have read it twice.
If you happen to have the intake off again for something I would check a couple of valves again for clearance being sure the lifter is on the cam heel for each one you check. But the issue is more likely a vacuum leak somewhere. Also, if the cam was not degreed when it was installed there is always the possibility of the cam being off or the timing gear not being marked correctly.

Last edited by JSeery; 11-05-2020 at 12:50 AM.
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