HD 25 Carb percolting

[lloyd]

Yes. The cam should fit tight inside the rotor and the outside of rotor should have gaps inside the rotor casing. Rotor in the photo looks like the wrong one.

[chacha53]

Eureka! I figured it out!
This motor was given to me by fellow who had been given the motor by somebody else. He had absolutely no history to pass on. I have been tinkering with it for months. I finally got it to run but it always overheated. No water coming out with the exhaust. I replaced the pump rotor, the water tube grommet, confirmed that all water passages were open, but still no water came out with the exhaust. Several times while it was running, I removed the drain plug at the base of the head to observe how much water was being pumped. There was always a lot of hot water spewing out under air pressure around the plug threads as I loosened the plug, followed by a flow of cool water when the plug was removed. I began to wonder why was the hot water under pressure and spewing back in the wrong direction from what I thought the flow should be. I again removed the head and also the carb. I traced what I thought should be the water flow and then I found it. The passage through the exhaust cover connected to the carb was blocked by the gasket. Both the water inlet and outlet that directs the water to the exhaust were blocked. I used my office hole punch to punch out two holes, reassembled and started the engine. Warm water spewed out with the exhaust from the holes in the midsection as it should. The carb stayed cool and no percolation!
Someone sometime in the past had installed the wrong gasket. It was a perfect fit, but it blocked the water passages. See pictures attached. The holes that I punched are indicated by arrows. The gasket looks factory, not homemade. Maybe for a different model?

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[bobw]

Once again, persistence prevails. I know you’ve been fighting this for a long time now, so congrats on figuring it out and getting it to run properly. You can see the imprints of the 2 blocked holes on the gasket – good find. Not sure what other gasket would be interchanged on that model but I know the power head base gaskets on some mid 50s model can be similarly interchanged with the same overheating result.

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."

[shane-r13]

Well thats great info. I’m going to have to tear mine apart thats having that issue and look at it now. Thanks for the update.

[chacha53]

Shane. How could you hear gas boiling in the carb while running? My engine makes so much noise as to drown out any other sound. If the gas is boiling you will see it bubbling out of the top of the carb around the float needle sticking through the top. Do you see it doing that? If you have a mist of water coming out the exhaust holes on the midsection then I think your cooling system is working. If you’re engine runs for awhile then stops, I would bet it’s a carb issue.

[bob-d]

Good find, congratulations!
Bob D

[aquasonic]

quote Chacha53:

. The gasket looks factory, not homemade. Maybe for a different model?

I’m thinking that the gasket from your motor is actually homemade, and the maker forgot the cooling ports. I have a N.O.S. Gasket PN 43-221 and took a picture of it for comparison. Notice on the picture of your gasket, some of the finer details of the mating surfaces have been simplified.

[chacha53]

You’re right. Big difference. Agree, mine was homemade. I bet that is why the previous owners gave up on it and just gave it away! Had it running a little while ago. Ran the gas out of the carb at slow speed. Hot water coming out of the exhaust. Just put, put, putted along. A really nice running motor.

[aquasonic]

Happy to hear that! You certainly "paid your dues". That was a very unusual problem, but you didn’t give up. Nice going!

[chacha53]

Thanks everybody!

[Author]

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