Motor runs great cold, once warm...not so great

[mstrud]

I was out on the lake in my toon with a johnson on the back. It did this to me last time i ran it, but when i get the motor running and get it good and warmed up it RPMs drop down to a rough half idle and barely runs @ WOT. It seems to go away once you let the motor cool down, (by that i mean tilted up out of the water for about 30 minutes) It did it to me several times today. I originally thought it was induced by excess water up in the motor (the boat had pretty heavy spray coming up off the transom.) shorting out something in the ignition, so i ran it a scoash above idle with no transom spray, eventually it did the same thing so im thinking its something that happens when the motor finally get warmed up. So what could this possibly be? The ignition is all new, id have thought its ignition related but i dont know, are there any ignition parts notorious for failing once it gets hot?

 

[The-Machinist]

Re: Motor runs great cold, once warm...not so great

What model johnson do you have?

 

[mstrud]

Re: Motor runs great cold, once warm...not so great

VJ50TLETB, sorry about that.

 

[jtexas]

Re: Motor runs great cold, once warm...not so great

Been like this since you got it?
Done any recent maintenance to it?
When was your last carb rebuild?
Checked your compression lately?
Fuel line holding pressure?
Fuel tank vent open?

Rather than try to guess about what it could be, let's narrow it down.
After it starts acting up, see if it picks back up if you push the key in (push-to-prime), or pump the primer bulb. Then check to see if you have spark on both cylinders.

 

[mstrud]

Re: Motor runs great cold, once warm...not so great

i bought it not running a few months ago, put in new ignition parts, timer base, power and coil pack. just short of the stator its an all new ignition. ive been working on it for the past few months. when it started acting up on me the other day was really the first time ive been able to take it out on the water, other than just dropping it in and doing a once around the lake to find what else wasnt working. compression is 150 on both cyl, it's never lost fuel pressure. spark was able to jump more than a 1/2 inch gap when i redid the ignition a month or two ago. the ball's fine the tank is fine. I'm thinking it has to be one of those new ignition parts i put in, but i dont know.

 

[jtexas]

Re: Motor runs great cold, once warm...not so great

Powerpack can malfunction when it heats up. Should be easy enough to rule out ignition - just warm it up & check for spark when it starts misfiring.

Didn't see carb rebuild mentioned in your bill of work.
Consider that it might be flooding due to stuck/worn float valve(s).

Also missing is water pump; if you don't know the age of the impeller or if it's more than 2 years, highly recommend replacing it now. Have you tested your overtemp horn?

 

[mstrud]

Re: Motor runs great cold, once warm...not so great

no i havent tested the warning horn. The mix is fine, and it pisses great, as i just rebuilt the water pump when i slapped on a brand new lower unit, a few weeks ago. So i dont know what the horn would be buzzing about, its **** water is never really warm. True the carbs are my are about the only thing on the motor ive yet to attend to. It just hasn;t seemed to be an issue.

 

[CharlieB]

Re: Motor runs great cold, once warm...not so great

You could have wisely spent your money on a DVA meter and tested your ignition before buying electrical parts.

You really do need a spark tester also to test spark at a 7/16 gap once the condition begins to appear. Search this site for directions on building your own spark tester.

It is possible that you have a defective new module OR that the insulation on the stator is breaking down with heat after running for a while.

Test, Test and Re-TEST until you prove your problem part.

 

[mstrud]

Re: Motor runs great cold, once warm...not so great

I had a meter, and it came in handy when i replaced most of the ignition. It was only 3 dollars n change at harbor freight, that probably explains why it no longer works. Anyhoo, i borrowed my dad's and have discovered the power pack is to blame, so kudos to whoever put it out there. As well as the people at CDI, they seem like they're easy to deal with. Now i play the waiting game once more.