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1976 85 hp Javelin power issues

R

repohorse

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I have a 1976 Johnson Javelin 85 hp motor. The motor starts and runs well until I want power. I took it out for the first time last weekend. It ran perfectly until I shut it off. When I started it again it started fine but does not seem to want to take off like it should. I get about half throttle speed out of it at full throttle. Doubt I could pull a skier up. When going full throttle it is like it wants to run better but can't, lurches a little bit and runs steady but does not run smooth. Seems to run just fine at slow speed. I was wondering if someone has an idea of how to fix the problem. Last summer I changed the water pump and it has not been the same since. There was very little of the old pump left. I found chunks of it in the water lines at the back of the motor, not sure if that could be making a difference. I put new gas line and new spark plugs on last fall. The filter and pump seem very clean.
 
Check the compression of each cylinder. Do you have loud snapping blue spark at each plug wire end?
 
guyjg said:
Check the compression of each cylinder. Do you have loud snapping blue spark at each plug wire end?
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compression was 100 psi on 3 cylinders and 92 on the other one. The spark plug in that cylinder didn't seem to have the same color as the other 3. looked less fired. I didn't have help to check the spark will do that tomorrow.
 
repohorse said:
compression was 100 psi on 3 cylinders and 92 on the other one. The spark plug in that cylinder didn't seem to have the same color as the other 3. looked less fired. I didn't have help to check the spark will do that tomorrow.
Click to expand...
I checked the spark and every plug jumped at least 1/2 inch and I think it was a blue spark. Hard to tell when testing outside. I guess the only other thing left would be a gas issue right? Would rebuilding the carbs help. The filter and the pump looked good. There wasn't any dirt in there. I only use premium gas non-oxegenated.
 
I checked the spark and every plug jumped at least 1/2 inch and I think it was a blue spark.
Click to expand...
Rebuilding the carb can't hurt but one carb is used for 2 cylinders. It could be as simple as one bad spark plug or wire or coil. I had an RPM loss on a merc. 115 HP and it turned out the single carb jet was plugged and one reed was held open w/a chunk of fiberglass debris. In your case it is a lot of work to get to the reeds...you may need to check. A spark board will let you see all sparks side by side for comparison. They all should be loud snapping blue sparks that jump a 7/16" gap.
 
Each cylinder has its own carburetor bore and jet.--Therefor a plugged jet will starve one cylinder of fuel and of course oil as well.--A rupyured fuel pump diaphragm will also flood one cylinder with too much fuel.----Make sure all carburetor jets are clean before running the motor again, as serious damage can result with iffy carburetion !
 
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