TOPIC: 1966 Merc 500 intake

Would a leaky intake gasket cause a motor to fail at full throttle,this is the.same motor I have been having trouble with all summer,I see air bubbles at the crank case seam,. Can this be serviced with out removeing power Head?

It would have to be a huge leak. Leaks along the crankcase/intake joint are more likely to cause problems at idle.

No way to permanently fix this except to pull the powerhead, split the cases, and reseal. You might be able to fix it temporarily by cleaning/degreasing the joint and using some Permatex MotoSeal Gasket Maker or equivalent.

www.amazon.com/Permatex-29132-MotoSeal-Ultimate-Gasket/dp/B000HBGHKE?th=1

This sealer is not fuel-proof, but it's more resistant than your garden-variety RTV. Once fully cured, it might at least last long enough for you to do an op-test on your 50hp.

With the intake cover separated from the block, after cleaning and degreasing the surfaces, use a very very thin coating of Loctite/Permatex 518 anaerobic sealer on the block flange only. Torque to spec and let it cure for at least 24 hours (more if cold in the shop).

What is your Merc doing at full throttle? That might help us figure out what's going on.

HTH........ed

Motor will start with warm up lever rev up and die, will run at idle but not good.I first thought it was a fuel pump problem ,that is replaced,also new fuel lines,carbs look clean with no visible obstructions,ran perfect after changing fuel lines went tubing and everything. A few days later it failed again.I keep thinking there is not enough vacuum to the fuel pump.this motor is a user every summer for at least ten years ran good last year.I posted last month under 1966 merc500 fuel pump problem., thanks for your help.

Have you cleaned and set mag ? set points .008 - .010.

A leaky crankcase can cause vacuum problems, just depends on how bad it is. One way to eliminate poor vacuum as a problem is to pump the primer bulb and if the problem goes away, you've got a fuel issue.

But I wouldn't expect any vacuum leaks or internal issues to be intermittent. Since you got it running good for a few days, that means it's more likely an external issue.

Primer bulbs are known to go bad too, and can have sticking check valves that will cause poor idle quality. If you haven't replaced the fuel line on the portable tank, and it's the "alcohol-resistant" type of material, check the innards for deterioration. The type of line with clear inner liner has a tendency to turn "gooey" and either block fuel flow or send a bunch of gunk through the system.

Definitely check the magneto/points as Dave suggested. These engines can be quite finicky if the mag isn't set up properly. I've had one idle poorly and found wear spots on the points cam. Was enough to throw the dwell off and run bad. Replaced the magneto shaft (which has the points cam built-in) and she ran like a top.

With the mag apart, also check the condition of the ignition coil. Cracks are bad and can lead to arcing, causing poor running. A coil with any cracks at all should be replaced. You'll want to pull the coil out of the mag housing to be able to inspect it thoroughly.