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Merc 9.8 110 no power in gear under load

MercyMerc

New member
Hi all, I've got a 1973 Merc 9.8 110 series. Last year I got it from a friend after 20 years of storage. Cleaned the carb, replaced gear oil, new plugs, the wires were all corroded so I replaced all wires in system with new wires, same gauge, brand new tank and fuel line, new impeller. Worked great all last summer.
Recently this summer the Merc was bogging down like crazy under load, at first it was sputtering, losing speed then picking back up again, at its worse it was really bogged down, no faster than walking pace. I took the carb out and cleaned all over again, every jet and hole. Back on the water and no difference. When I was trying it I primed the bulb a bit and it took off! Yesterday I replaced the fuel pump gaskets and took it on the water, it worked like new...for a while. At some point I slowed down and could never get back to speed, bogged down again. Any thoughts where to look next?
 
It is a 2 stroke motor and there may be issues with crankcase compression.----Check cylinder compression and check spark.----Spark must jump a gap of 3/8" or better.
 
Same tube. Pump is attached direct to carb but from inlet to pump is original hose. I had gotten some replacement tube but the ID was way too big
 
My bad the 1973 uses the manifold vac port for the fuel pump pulse. Did you surface the carb flange and install a new gasket?

I installed the fuel pump gasket kit. That's when it worked great...until it didn't. Cleaned all the sealing surfaces when installed
 
When you installed the carb did you use a new gasket? If not pull the carb and on a glass table with 220 grit paper surface the flange by pulling the carb in one direction only until it all shines the same . Then install a new gasket and pull the carb down slow to good and snug. Too many people overtighten carbs down it bends the ears and causes leaks in the flange gasket.
 
Sounds like it is running on one cylinder.-----Do the inspection and trouble shooting.

It does sound a bit like that. But given the story so far and the (temporary) improvement right after a fuel pump rebuild, I have a feeling it's further up the chain of intake. Just a thought... everything is worth looking into with a motor built in 1973.
 
When you installed the carb did you use a new gasket? If not pull the carb and on a glass table with 220 grit paper surface the flange by pulling the carb in one direction only until it all shines the same . Then install a new gasket and pull the carb down slow to good and snug. Too many people overtighten carbs down it bends the ears and causes leaks in the flange gasket.

That is a great technique. I can see how that could happen with that particular flange
 
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