Martin 75

[edgartc]

my son-in-law gave me a Martin 75, with the carburetor in a box, he found it at a flee market. I cleaned and set the points, good spark now, good compression, and I have it together. It started on the second pull and runs pretty good for about 3 min. then sneezes and stop. then will only start if it is chocked, then it will run about the same amount of time sneezes and stops. I have tried multiple jet settings and I can make it worse but not better. I have heard about O-ring on the valves, could this be causing this?

[chas56x]

Yup. Order new rings from : https://martinoutboards.com/

[richardg]

Does that mean that exhaust gases are blowing by the rings filling the crankcase with an incombustable mix?

[outboardnut]

be sure to keep the same valve in the same hole when replacing the o rings

[garry-in-michigan]

That means the rubber "O" rings on the intake valves have gotten hard and are no longer sealing when warm and the stem expands. This lowers crankcase gompresion & leans out the fuel/air mix which slows the flame front in the combustion chamber so it is firing when the bypass ports open causing a "Sneeze" through the carburetor. . . 😉

[edgartc]

Thanks for the info, I went to Larson’s outboard but couldn’t figure out how to find the O rings, I left a message hope they will get back to me tomorrow

[jpatti75]

I recently bought the poppet value o-rings from them. I imagine Russ still carries them, and I remember them being fairly reasonable, too. Might want to get a new intake manifold gasket since you’re going to have to remove it to get at the poppet valves. Had the same issue with my Martin 75, and the new o-rings solved the problem. Those Carter carburetors are very testy, in my opinion, so make your adjustments in small increments when you’re dialing in the idle to get it running at optimum.

JP

[frankr]

Well, I’ll stick my neck out and say it sounds more like a fuel flow shortage to the carburetor. Gas isn’t flowing into the carburetor as fast as it is being drawn out.

[Buccaneer]

Is that carb one that you have to turn the low speed jet "Clockwise"
to richen the mixture? I’ve been a victim to that cruel hoax more
than once, lol.

Prepare to be boarded!

[amuller]

Not sure, but I think those O rings are a standard size you can likely get from an assortment or at a hardware store. Viton rings might last better than the standard SBR.

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