Thread: 15 hp johnson lack of power

I have a 1974 15 hp johnson with a lack of power. it has good compresion and it is not running on one cylinder. the motor starts and idles pretty good but but will only push my 14 foot flattbottom 5-7 mph. i have been told it could be the high speed jet in the carb but i am not sure. . also read on the net where a guy had a similiar problem and replaced the points and he regained the lost power but i don't think the points would be a problem if it starts and runs without dying would it. any suggestions or pointers would be appreciated.

You have checked compression, but what about the ignition system. Its best to trouble shoot your problem step by step and not grope blindly for straws.

Why do you think one cylinder is not running? Have you checked for spark on this cylinder? You can have bad points, bad plug, bad plug wire, bad coil...

Best to check things one at a time.

Fish Taco i said it is not running on one cylinder because i have already checked that and figured it would be one of the first things mentioned. thanks for the input

Did it just start doing this? Has the motor sat for a while?

i purchased the boat and motor last spring and it has been doing it every since i bought it and i have yet to fix it because it is operational but is just severely lacking power. i use it about once every two weeks so it is used fairly often.

Rebuild the carb and fuel pump.

If you have spark is it strong? I'm thinking maybe flaky condenser. Had one of those give me a fit once. Weak or cracked coil can sap energy weakening spark also. I always put new ignition from coils to plugs and took the bowl off the carb for a quick inspection. If there was any, and I mean any varnish buildup visible, have it redone. Make sure the tech will soak the casings in the super cleaner(boil) to clean all the orifices. After that mine always gave me good service. If yours is a low profile evin or johnny, let the tech do the carb tune on it. They have to be set up to run with the cover on. If you tune the carb to run good with the cover off, the air flow( or resistance or something like that) changes the tune of the motor once the cover is on. My brothers been foolin with his for 3 seasons now. Keep us posted, I'm curious where your problem lies.

I had a '74 25hp Johnson, and I personally would replace the points and condensers and reset the timing and check the linkage to the carburetor. The timing could be off when accelerated because the timing plate has to advance the marks to keep up with the engine speed. If you need any information, I have the complete Johnson manual for all 1974 engines. I could copy and email the pages from the manual to you, but it will take me a day or so to get it to you. Let me know. Rollcaster.....................

I would also be sure the carb is opening all the way up when you twist the handle to WOT. Might just need to adjust the linkage so the carb opens all the way.

thanks for all the info got it fixed today. all it took was a good carburetor cleaning.