25hp dies at full throttle

[perkdp]

1973, 25 Evinrude Runs fine from idle to WOT. After a short time it slows down to an idle coughs/sneezes and sometimes dies. Will idle or low rpm for as long a you want it to.
I put a new float and valve in the carb which looked brand new inside.
When it starts to slow down, I squeeze the bulb, which is firm, but it doesn't help.
I'm thinking trash may be pumping up on the tank side of the fuel pump screen at WOT and blocking the flow to the bowl. What do you guys think ?

 

[lindy46]

Re: 25hp dies at full throttle

Check spark. You may have a bad coil which cuts out once it warms up. If it's running on one cylinder it will still idle ok.

 

[Cofe]

Re: 25hp dies at full throttle

Sounds like the thermostat may not be working. If the engine overheats at wot, the motor goes into slow mode. The engine temperature should be at 145 degrees. If you burn your hand on the motor head when this happens, it is overheating. Borrow a digital temperature gun (if you don't want to get a possible burn)and check if possible.
You may also be correct in thinking you have a fuel related problem.

 

[bktheking]

Re: 25hp dies at full throttle

the motor goes into slow mode.

No slow mode on a 73.

 

[kbait]

Re: 25hp dies at full throttle

Check the screen at the fuel pump. That would cause your symptoms, and pumping the bulb may not help. If it's clear, next use a golf tee, or something plastic, to stick in the end of the fuel connector (motor end) to keep it open (not attached to motor). Squeeze the bulb and if fuel comes out easily, then the screen in the tank is unobstructed.

 

[tashasdaddy]

Re: 25hp dies at full throttle

clogging high speed jet, http://forums.iboats.com/showthread.php?t=299680

 

[kenmyfam]

Re: 25hp dies at full throttle

Sure sounds like a blockage.

 

[bktheking]

Re: 25hp dies at full throttle

How do the plugs look, any of them clean? How about compression check?

 

[14ftgrumman]

Re: 25hp dies at full throttle

What tashasdaddy said and it sounds like the lean carb sneeze". richen the adj. and read top secret files.

 

[perkdp]

Re: 25hp dies at full throttle

thanks for the feed back... I haven't had a chance over the weekend to check it out. But will post my findings when it do.

 

[perkdp]

Re: 25hp dies at full throttle

I've been kind of busy.... the fuel pump screen was clean. I did pump one spec of trash with the bulb while I the line off the pump.
Motor Idles fine in the barrel. Haven't had it to the lake yet but now suspect the float level is set wrong and not allowing proper fuel level.
I probably need to fill the bowl and run with the line off the carb to see how well the pump is working. Or is there some other volume test for the fuel pump ?

 

[soundchaser]

Re: 25hp dies at full throttle

definitely sounds like a high speed blockage.

Coil wouldn't idle after it started going south.

Pump was a good thought, But if that's not it.

It would have to be a blockage in the High speed circuit.

try different tank hose. And make sure vent screw is open.

 

[perkdp]

Re: 25hp dies at full throttle

Took it to the lake yesterday just to see if I have made any difference and to try a gravity flow fuel supply I rigged to isolate the fuel pump. Started raining before I tested the gravity flow rig. So, I have not made any difference yet.
Can run wide open for about 1/4 mile. When it starts to fade, I can let off and idle as long as I want. Then WOT for another 1/4 mile. I'm still thinking clogging jet and / or float level is just off enough that it won't let the fuel pump keep up. I'll have to go into the carb to adjust the float I may as well completly clean and kit it.

Any tips on how best to set the float level ? I don't have a guage.

 

[14ftgrumman]

Re: 25hp dies at full throttle

Invert float bowl and adj. float level even with float bowl.

Been a while since I did one, if I'm wrong, someone correct me. please

 

[perkdp]

Re: 25hp dies at full throttle

thanks. i'll give that a shot.

 

[kbait]

Re: 25hp dies at full throttle

On one I had to adjust the float a wee bit closer (hold more fuel). Still don't know why, but the guys boat ran fine after that, and had the same symptoms as this one. I don't necessarily recommend going against OMC standards!

 

[perkdp]

Re: 25hp dies at full throttle

spent new years afternoon doing some carb work... did not find any trash to block the high speed jet. blew carb cleaner through every port i could find and all were open.
adjusted the float to open quicker and allow more fuel in the bowl. adjusted the float stop to allow it to open farther.
took it to the lake sunday afternoon and still have the same problem.
i've had some headaches before but this one is becoming a migraine.
i have no way to test coils and condensers without finding a known good spare and swapping. and, this just doesn't seem like a spark problem to me.
once the motor shuts down, i can touch the head and leave my finger there for probably 10 seconds and it is spraying water out the indicator.
i guess a fuel pump rebuild is next.

 

[tashasdaddy]

Re: 25hp dies at full throttle

a spark tester will tell if the coils are good. spark should jump atleast 3/8 inch, preferable 7/16.

 

[blimp]

Re: 25hp dies at full throttle

check for water in cyl, a buddie's boat had this problem. higher rpm = higher water pressure = cyl getting killed by water. Check for wetness on plug after it dies, could be head or exhaust gasket.

 

[northernmerc]

Re: 25hp dies at full throttle

This sounds like the motor is overheating. Are you sure it does not have SLOW mode? Is there a wire running to the head not far from the spark plug?

If you are out of ideas, take out the thermostat and try running it like that. You might be surprised at the results.