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Fixed Jets

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2 Months ago I paid $150 to have my 1984 40 hp Johnson carbs cleaned, after many failed attempts my me. Today the thing was running terribly for hours (trolling), killed, and refused to start. I got it going, but it is doing the same thing as when I bought the motor 3 months ago. I can still get it to open up by feathering the throttle, but it is getting worse. I think is is because of the stupid fixed jets in the thing, they are set WAY too rich, not to mention the holes are so small. Is there anything I can do? I run 91 oct. non-oxy gas, 50:1 full synthetic oil, fuel stabilizer, and I strain the gas when it goes into the tank. I am at my wits end with this motor. I've had the thing runnning acceptable (not good at all) for a week, and then it was down hill again. Do I have a lemon, am I doing something wrong, or are "big twins" really the worst ouboards ever made? mad

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What do you mean by. "I can still get it to open up by feathering the throttle."

AND." they are set WAY too rich, not to mention the holes are so small.

The set jets are few sizes and the standard set is for sealevel up past our 1100-1200 ft elev.

Have you pulled the plugs?are they wet?what do they look like? Have you checked the spark with a real spark tester?Did it jump a 1/2 inch gap with a bright blue spark?

Has anyone checked the timing? rare it would be off but a check would ease ones mind that its right.

There are so many things the lowspeed fouling could be caused from.You just have to trouble shoot one thing at a time.guessing can be expensive.

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I went through everything when I bought it. Everything is in perfect condition. Compression on the cyilinders is 159 and 163 psi. New plugs, perfect gap, everything is fine. The issue is the carbs, just like last time. I feel it is a very poor design. I took it off earlier, and put my old 1972 18 hp evinrude back on. I has been sitting for 4 months, and I don't think the motor even turned over once before it started. grin I wish I could trade my 40, for a 40 hp version of my 18.

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In my experience, the moment that I'm convinced that it's one things is when the problem is destined to be something else. Don't rule anything out...ever.

As the great philosopher Mr. Spock once said, "Once you have eliminated the impossible, whatever remains, however improbable, must be the truth."

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Jentz pretty much nailed how to track down the problem. I would follow his advice.

One thing to add since you are convinced this is not an ignition issue. Run the motor in the RPM range where the problem is worst, then hit the kill switch and pull the plugs. They will tell you if it is running too rich or too lean, and which carb to address. Once you have isolated the problem, you can start looking at what the carb(s) are doing. It is likely that the real issue is a lean condition caused by either a fuel obstruction or an air leak somewhere in the fuel system. Have you checked your tank pickup, and the hose o-rings?

If you do not want to tackle this one yourself, try contacting Tom Dingman in Annandale. He is very good with this type of problem and can likely get it fixed for you.

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