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1975 Johnson 50 Engine Issue

L

lohrdg

New member
My 1975 Johnson 50 Engine bogs down at mid to full throttle after a few minutes of running. I have replaced the water pump, plugs and coils. The engine temp is normal (gauge and to touch). Clean fuel and tank was verified. Took it to a shop and they said they put it on a dyno and were able to simulate the same problem. They said the fuel system tests good, compression is 140-145 per cylinder and think it is electrical. They swapped out the stator with a new one with no change. They believe it is the timer base sensor coil and are waiting on the part to ship. My concer is this maybe a carb issue. I don't know much about the dyno test except that it gives hp info. Will the dyno test confirm proper carb function? Any other advise?
 
Sounds to me like the shop is replacing parts and not doing a proper diagnostic. The compression is good the next step is to do a spark gap test. The spark must jump a gap of at least 7/16 inch open air gap on the plug wires. Do you know when the carb was rebuilt last? It could be a simple as the fuel pump diaphram is getting stiff and not able to keep up with the demand. If spark plugs are powdery white I would rebuild the fuel pump and carb and replace all the fuel lines. Alot cheaper than changing electrical parts without confirming they are bad. Make sure they give you the old stator and trigger if that does not solve the issue. If they cannot produce the parts do not give them a dime.
 
Spark test was good on both cylinders. Nice crisp spark. I have replace all fuel lines and new fuel pump. Carb was rebuilt early this season. Still trying to understand what the dyno test does. Will the dyno test confirm proper carb function?
 
Have you tried running on a different fuel tank? I sounds like fuel restriction to me. Did the spark jump a open air gap of 7/16 inch with a open air spark gap tester? Just looking at the plugs does not tell you anything.
 
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