1990 40 hp slow power off and on

[fourbox43]

I have a 1990 40 hp when i am out on the water and i get it started and let it warm up, I start off but not fast but when i do go full force it runs like a 15 hp then after a few moments it jerks back and forth and then it takes off sometimes i loses the power and it comes and goes can someone piont me in the right direction checked the compression i have 115 in the top and the bottom is 113 and i do have spark from both plugs

 

[Rick.]

Re: 1990 40 hp slow power off and on

I think you have intermittent spark at best. You should hook up a timing light and take it out and test it when it's giving grief not when it's running fine. Best of luck. Rick.

 

[boatsngoats]

Re: 1990 40 hp slow power off and on

Intermittent spark is a likely cause.. but hard to diagnose without the proper equipment and/or replacing the stator or powerpack(s)

another thing to do to (make sure its ignition related) is to continue to squeeze the prime bulb while running. If, while squeezing, the engine picks up and runs like it is supposed to at WOT.. you could be having a fuel pump problem or a restriction in the fuel line.

 

[5150abf]

Re: 1990 40 hp slow power off and on

Welcome to iboats.

Have you tried tapping the choke while it is doing this, that will diagnose a clogged carb if it suddenly runs right with the choke.

Also pop the hood off and start looking for any wire that may be touching and shorted, do this running and NOT in gear, you don't want it to get a sudden burst of power while you are purched over the engine at 20+ years old the sheathing on the wires may be getting brittle.

Check the coils good for any cracks and get a spark checker from any auto parts store, they are pretty cheap and really the only way to know if you are getting a good spark, it can jump a plug and still not be good enough, it needs to clear a 7/16'' gap.

A freebie thing is to clean all your wire connections really well, do this one wire at a time so you have no chance of getting one back in the wrong place.

ANd of coarse an OMC factory servive manual is highly reccomended, NOT Clymers a Seloc or anyhing on CD, a factory service manual, you cna get them here at iboats or check Ebay.

 

[fourbox43]

Re: 1990 40 hp slow power off and on

ok i know ford big blocks and chevy small blocks where do i check the timing at and which wire do i use top or bottom

 

[boatsngoats]

Re: 1990 40 hp slow power off and on

you have to use the Top cylinder.. That is #1. and there should be a timing pointer at the flywheel.(carb side, I think.) otherwise.. you should see kind of a triangle pointer that points at the flywheel. You should see raised #'s on the flywheel too. I recommend taking some white out or a white grease pencil/marker and color those #'s. They are wicked hard to read when its spinning.

Also, be careful. You have to be just about on top of the engine while she is running to check the timing. I've kinda slipped on the wet ground and almost ate it a couple of times..

Then a again... i'm not that smart to have learned the 1st time, and its kinda a "thing" for me.