Fluctuating Vacuum

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veteransgarage
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Fluctuating Vacuum

Post by veteransgarage » Sat Jul 24, 2021 7:36 am

Need some advice - better education:
I’m working on a 4-134L engine. Rebuild from the block up. Professional Machine shop boiled and magnafluxed the block. All new bearings, rings, etc. Installed new hoarded valve seats, valve guides, tappers, valves, springs, retainers, etc., lapped valves and set at.016. Decked the block and head. New Carburetor, distributor, manifolds planned and magnafluxed. All new gaskets. All 4 cylinders at 110 psi.
SO……engine starts and runs “ok” but vacuum fluctuates at about 18 no matter where I set the timing.
What am I missing. What causes vacuum fluctuating,???

Thank you
Joe


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Scoutpilot
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Re: Fluctuating Vacuum

Post by Scoutpilot » Sat Jul 24, 2021 9:46 am

From where on the motor are you taking the vacuum reading? It should be from the intake manifold and not the carb.
'70-'71 'A' Batt., 377th FA, 101AB
(Slicks and LOH's)(Col's LOH Pilot)
'71-72 CHARLIE TROOP,
16TH AIR CAV, 1ST AVN BDE (AEROSCOUTS)
LOW LEVEL HELL.
'46 CJ2A
'47 CJ2A
'48 CJ2A
'48 B1PW126
'69 CJ5

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Re: Fluctuating Vacuum

Post by veteransgarage » Sat Jul 24, 2021 10:50 am

Vacuum gauge connected to inlet manifold (top to the right of the carb - not on the carb).

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YLG80
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Re: Fluctuating Vacuum

Post by YLG80 » Sun Jul 25, 2021 6:48 am

An indication..

2C045035-4203-4ABA-AF5C-0F8A25037334.jpeg
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Scoutpilot
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Re: Fluctuating Vacuum

Post by Scoutpilot » Sun Jul 25, 2021 8:22 am

How many miles/hours on the motor since rebuild? Is the carburetor tight to the manifold (30-35 lb-ft of torque)? Have you run a vacuum leak test with starting fluid or propane? What is the idle RPM?
'70-'71 'A' Batt., 377th FA, 101AB
(Slicks and LOH's)(Col's LOH Pilot)
'71-72 CHARLIE TROOP,
16TH AIR CAV, 1ST AVN BDE (AEROSCOUTS)
LOW LEVEL HELL.
'46 CJ2A
'47 CJ2A
'48 CJ2A
'48 B1PW126
'69 CJ5


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