1974 Johnson 15 Seahorse not cranking have done everything

Have changed plugs, they’re firing. Got carburetor rebuilt and has fuel flowing in it. Also just replaced the starter. All this in the last few days. I can’t think of anything else to check? Battery is good also. It’s turning like a top, but just not catching and firing up. *

Memphis465 said:

Have changed plugs, they’re firing. Got carburetor rebuilt and has fuel flowing in it. Also just replaced the starter. All this in the last few days. I can’t think of anything else to check? Battery is good also. It’s turning like a top, but just not catching and firing up. *

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I can tell you the first steps that should be followed: Do a compression test with plugs out. Post the numbers. Make sure your spark will jump a 7/16" gap with a bright BLUE spark. Check all fuel lines and connections for air leaks. The experts will be along with more advice, but you can help them help you by posting your compression numbers and confirming bright blue spark.

Also, ensure the throttle is fully to the neutral stop, for starting. Ignore all writing on the twist grip.

Verify that when you pull the choke lever the choke butterfly actually closes. Sometimes you hear the click and everything but the butterfly gets caught up in something and the choke never closes. You can crank till the cows come home but without choke you will never start that thing.

Make sure your link and sync with the carburetor is set right. On the throttle cam that turns and pushes on the carb's roller, there is an arrow. That arrow should be in the middle of the carb roller JUST as it touches the roller. If not there are two hex screws under the flywheel on the starboard side that adjust it. With the flywheel on you will need a very thin 5/16" wrench to loosen the hex nuts.

If none of that works, take a little of premix gas or seafoam and drop/spray it into one of the spark plug holes. Screw back in the spark plug as quickly as you can and see if you get any pa pumps out of it. If it starts you probably have a choke problem. If it papumps you probably have a fuel delivery problem and if you get nothing you probably have a spark or compression problem.

I should add that "plugs firing" does not mean they are firing at the right time. Make sure no one has mixed up the two clips coming down from the flywheel to the spark plug coils. If they did, the plugs would still be firing, but when the piston is at "bottom dead center" and not the preferred "top dead center" that tends to make the motor actually run.

The other issue with spark is your point gap. Did you verify that the points are set correctly. If they are not set right, just like the above, you can see spark on the plugs, but that spark is not timed right. Perhaps not as bad as bottom dead center but even if it is a little late, during starting this can be a big problem. Your point gap needs to be at 0.020". Over time it tends to decrease as the rub bar wears away. It should be reset about every 3 years on that motor, if you ask me.

Update on this: Took it to the shop everything is in working order except for a cylinder is not firing and they’re kind a dumbfounded. Go figure...

Oh come on, a cylinder is not firing and they can't figure out why it doesn't? What kind of shop was that?

^^^^ this...

What kind of a shop? Many shops dont like to work on those old motors. So with spark on only one cylinder try to put the wire coming from the stator plate that is running to the coil on the cylinder with good spark, and put that wire instead to the coil on the cylinder with NO spark. If you then get spark, we can look under the flywheel for the problem and we can rule out a problem with those final coils. There was a good discussion here a couple weeks back with regards to a spark problem on a 9.9 or 15 that was the same vintage as yours.

From Leroysramblings.com, normal repairs:

”Hard Starting : These motors can be hard to start unless the choke is staying fully closed while starting. Verify that the stainless steel tang that holds the plastic choke lever in place is doing its job, after a while they need to be re-bent back in place to apply enough tension on that choke rod notch to hold the choke in position. Also verify that you have replaced the choke knob right. If your choke knob shaft was installed upside down, the choke butterfly will not completely close, thereby not being able to choke the engine when doing a cold start. The wider slot on choke knob shaft (the connection point to choke butterfly lever) goes up.”

I had an expert upgrade my 1976 15hp to a 1977 ignition with CDI. But he installed the choke lever upside down and it wouldn’t start. When that was corrected it starts easily with the following steps: fully choked, crank a few seconds until it “coughs” as if about to catch but doesn’t; then unchoke it and it starts every time after a few seconds cranking.

Hope this helps.