Thor and Sea King poppet valves

[opposedtwin]

How do poppet valves work? Didn’t evinrude have some of these on their motors as well? I don’t think johnsons ever did. So this first one is from a 1938 Thor but I know the pre-kiekhaefer sea kings had them too. How do they work and what do you need to do to get them functioning properly? This one has a stuck valve out front. Is that the needle valve for rich/lean adjustment?

• This topic was modified 3 years, 9 months ago by opposedtwin.
• This topic was modified 3 years, 9 months ago by opposedtwin.

[Buccaneer]

The ones I’ve seen have a tiny hole drilled into the valve seat, and
the crankcase vacuum overcomes the spring tension, sucking
the valve open, and hence fuel into the crankcase.
That valve on the outside may just be the fuel shut off, as I believe
the hole in the seat determines the amount of fuel, and rpm
increase in the motor is by advancing the timing…… at least
that’s how I believe my little Thor is set up, but I’m sure
the bigger motors with poppet valves are a little more sophisticated.

Prepare to be boarded!

[PM T2]

The lever sticking out front of that mixer is indeed the needle valve for adjusting the fuel mix.

With poppet valve carbs (or mixers, mixing valves, whatever you prefer to call them) the main things with the mixer is ensuring that
a) the gasket is sealing where it mounts to the crankcase
b)the threaded cap on top also provides a good seal to prevent air leaks into the poppet valve chamber,
c) the poppet valve itself is loose and not stuck to the seat,
d) the spring tension needs to be of a sufficient level that it will return the poppet valve to the close position yet allow it to lift off the seat during the intake phase, and
e) that the needle valve is not loose and flopping around and is allowing fuel to leak past it.

I would mention poppet valve lift/travel (how high it can rise off its seat) but with a Thor mixer, its not necessary because the Thor mixer has no way to adjust that amount of travel anyway.

One of the key elements in poppet valve miser operation is crankcase sealing. If the crankshaft bearings are worn and the clearances are too great, Thors are terrible for displaying behavioral problems that would make a preacher curse.

With the spark plug removed, rope the motor over and listen to the poppet valve. If it snorts or burps every time the motor turns a revolution, it should be functioning well enough to give you some hope of getting t he motor started….. assuming the magneto is working and cylinder compression is strong enough.

Hope this helps.

Best,
PM T2

He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...

[opposedtwin]

Very interesting explanations and recommendations! Thanks buc and pm t2!

[opposedtwin]

Here’s a pic of it disassembled. Does it look like it’s missing any parts?
Thanks!
Scott

[Buccaneer]

It looks like mine had a brass pin to prime the engine by lifting
the poppet off it’s seat to allow gas in the intake.

That piece of tangled up wire was someone’s attempt to stop
the gas line leaking. They wrapped wire around the fitting
at the carb then soldered around it. Doubt if it worked long.

Prepare to be boarded!

[Author]

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