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Starting Problems 1975 Johnson 70HP

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geoff

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" I have replaced the starter

" I have replaced the starter and am still having problems getting the engine to start. A friend of mine messed with the linkage and we believe the engine is not getting air when we crank it. It there a way to adjust that instead of having to take the cover off all the time. Also, the boat will run good for a while and then you can tell something clogs one of the cylinders. Can we clean the cylinders? "
 
Do a compression test and pos

Do a compression test and post the results.Check to see that spark will jump at least a 3/8" gap.You can run the motor at full throttle and check carburetor bores to see how the amount of fuel compares. (use a flashlight when looking into the bores )
 
" Hi Geoff,
As Sparky notes

" Hi Geoff,
As Sparky notes, do a compression check first so you know you're not chasing the wrong problem...
If that checks out (all three on the far side of 130 psi and within 5% of each other) then move on to the next stage. With the motor running, try covering one carb at a time and see if it makes a difference in performance. If covering any one carb makes no difference, then you've found the cylinder that isn't firing. If your hand comes away from that carb dripping in fuel, then it's probably not a fuel issue. Check the plugs and see if they're all a uniform color. If one is much darker or lighter than the others, then it's another signal that something is wrong. If it's dark and wet, then you've got an ignition problem. If it's light and dry, then you've got a fuel flow problem.
Check back here with your findings...
- Scott "
 
I have replaced all three spa

I have replaced all three spark plugs and have done a cold compression test. Each one has 100psi at the cold test. We have checked the spark and that is fine. I replaced the coils and boots. I know I am getting plenty of fuel because when we are done and run the fuel out of the lines it takes forever to stop the motor.
 
" Hi Geoff,
One of your car

" Hi Geoff,
One of your carbs could still be gummed up. One fuel pump feeds all three carbs, so it's possible it's running on only two of them. How did the plugs look when you removed them?
- Scott "
 
"Geoff..... When you are done,

"Geoff..... When you are done, DO NOT run the fuel out of the lines (engine). You have three carburetors. The top carb will run out of fuel before the others due to gravity if nothing else. The engine will continue to run on the other carbs. This results in at least one aluminum piston running up and down a steel cylinder wall with improper or no lubrication.... not a good idea!

Joe
"
 
" IN a two stroke,oil stays ar

" IN a two stroke,oil stays around in the engine for quite a while after the carburetor run out of fuel. IT is still a good idea to run the fuel out of the carburetors when taking a boat out of the water. ( I have been recommending this since 1968 ) "
 
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