1994 50 HP evinrude runs half power for a little while then runs great. WHY!?!?!?

[chckwgon]

I have a 1994 20 ft Lowes pontoon boat with a 1994 50 HP Evinrude that will run full power then cut out and run only at half power and idle like crud and the performance would never improve until I would bring the boat home. Using carb cleaner and low pressure compressed air I would clear out the lines. The next trip to the lake the engine would run flawlessly for a day then the next trip out the issue would come back. Last summer before the lake season I have rebuilt both carbs, replaced all fuel lines, spark plugs, spark plug wires, ignition coil, fuel filter, and have added an extra in line fuel filter. Now the boat will run at half power for about the first 20 min. of the day then start jumping until finally clean up and run great. My thoughts and past expierence with engines that electricaly things go from good to bad as the engine heats up, not bad to good. This has me stumped and very aggrivated with it. I'm open to all suggestions.

thanks

 

[AlTn]

Re: 1994 50 HP evinrude runs half power for a little while then runs great. WHY!?!?!

try an inductive timing light on each plugwire when the motor is running properly and then when it's running poorly...the strobe will indicate whether you've got an intermittent or no spark condition...fuel mix in a spray bottle sprayed into each carb throat..motor should bog at the rich mix..if it picks up, that carb is lean for some reason
Another thought...is the timer base moving freely when it's cold?

 

[chckwgon]

Re: 1994 50 HP evinrude runs half power for a little while then runs great. WHY!?!?!

I have already tried the spraying fuel into the carbs when trying to determine if the issue was isolated to just one cylinder. Spraying fuel into either of the throats resulted in RPM drop (each carb was not checked at the same time). I will give the timming light a try as well as checking the timer base. But, what is the timer base?

Thanks for the responce.

 

[cyclops2]

Re: 1994 50 HP evinrude runs half power for a little while then runs great. WHY!?!?!

Water in the fuel tank ? Runs great after boat sits or is running slowly.

Some people are going to get the bottom of the Ethanol fuel tanks. As it is phased out of use in Canada & the USA.

We would like to think that no one is adding to much " LEGAL " water to each stop in the fuel supply systems. Or stirring up the bottom with each delivery. Never buy from a station for 3 days. They tell me when the last delivery was. It does help.

So does using SeaFoam in the gas tank. I try that as soon as power is the slightest bit not right. Has always cured my 2002 5 L V8 & the 9.9 hp. Car to.

Rich

 

[adoseth]

Re: 1994 50 HP evinrude runs half power for a little while then runs great. WHY!?!?!

possibly a faulty overheat sensor causing limp mode?

 

[chckwgon]

Re: 1994 50 HP evinrude runs half power for a little while then runs great. WHY!?!?!

A guy at work said the issue could possible be a weak fuel pump? He said that it is taking a while for it to build up enough pressure in the line to supply the enigne at power. Does anyone agree with this possible cause?

 

[cyclops2]

Re: 1994 50 HP evinrude runs half power for a little while then runs great. WHY!?!?!

What can affect both high speed , middle & low speed ? What can run great for 1 day after a complete cleanout of the fuel system ?

Seems like a case of running on the water with the bouncing around causing a problem. I say clean the filter on the fuel pump, if there. Change the fuel tank with a KNOWN good running 1 from SOMEONE ELSE WITH NO PROBLEMS.
No help ?

You know it is electrical most likely by then. A bad one just like I had. Ran great for several short bass trips in the morning. But if I had a LOONG return run for lunch or supper. BINGO!! Conk outs. Figured that out...AFTER ..we found the problem. Then it made sense.
A few times , which did not sink in , I ran with the cover off & it ran longer on a long run.

 

[andrewddrennon]

Re: 1994 50 HP evinrude runs half power for a little while then runs great. WHY!?!?!

Does your gas tank have a check valve? Either way run it on diffrent gas tank and gas line. That will rule out alot of possible problems.
What happens if you squeeze up the primer bulb while its not running right? Try hitting the choke also. If either one makes it run better its a fuel problem.