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Bad Intake Manifold?

On those old Harley engines we would spray around the fitted surfaces and suspect areas and see if it affected engine rpm or ignition...it may provide a clue for you.
 
quickest way would be to just replace it.

If it is off, you can have a machine shop magnaflux it or use a similar system.

Last (time consuming) option would be to fab some block off plates and then check it with compressed air and a gauge.
 
If you can find some 2 plus 2 carb cleaner, spray it around the base of the intake with the motor warmed up and idling. (Be sure the hatches are open and the blowers running!) If the motor picks up speed, there's your leak. Be careful not to get the cleaner into the flame arrestor or it will trick you.

Jeff
 
The issue is hidden water leakage into the crank, right? Take off the intake and inspect it. I'd do a pressure test first, and don't forget to drain the block, both sides. You might get lucky and see a water trail from the defect. If the heads have ever been decked, you should also take some metal off of the intake. A machine shop job.
 
Thanks all. Pulled the intake again and looked it over to find nothing obvious. Got new intake bolts and reinstalled with no luck.....
More water in the oil and not to happy. FWC goes down while temp goes up and oil level too.
 
Uuugh! Before yanking the heads (or the motor) I'd try some NAPA sealer. Use the silvery kind in a tube that looks like aluminum powder. It worked grat for me on a car engine with a cracked head.

Jeff
 
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