1975 Evinrude 25

[Four22]

I have a 1975 Evinrude 25 horse, model 25502B that I’m trying to get running correctly.

I’ve replaced the fuel pump and lines under the hood, cleaned and rebuilt carb, points and condensers, spark plugs and checked coils. Also replaced water pump and thermostat.

The motor starts up fine with only a few pulls but after idling for 20-30 seconds it starts to spit and sputter and rev up on its own. If I pump the fuel bulb it’ll settle back down and smooth out for another 20-30 seconds.

I’m picking up a new fuel line and bulb today and have been running the gas can with the lid off trying to eliminate the possibility of a clogged vent.

What else could this possibly be? Could the hole through the power head where the fuel pump goes be clogged keeping the diaphragm from pulsing??

Looking for some other ideas to try if anyone has any suggestions.

Thanks all!!

 

[racerone]

I believe it is running out of fuel.----So check your fuel line o-rings in the fittings.-----Step #1 in trouble shooting is always the same.----Post your compression test numbers.----

 

[Four22]

Agreed definitely leaning out but can’t source the problem.

Compression was 120 in each cylinder.

I’ll report back after the new fuel line and see what happens.

 

[racerone]

When the carburetor bowl is near empty an outboard will rev up.----Test run with another hose and tank.-----Some cheap plastic tanks have issues with pick up tube inside the tank.

 

[kbait]

If you have an original metal tank, you could have a bad o-ring in the tank coupler..behind one of the ‘pins’. I test those tanks by hooking 2” of clear hose to a good hose coupler, connect to tank, and slowly suck on the clear tube.. if bubbles come up with the fuel, that’s your leak,

 

[Four22]

I’ll check that too. It’s is an old metal can that was used last year on a different motor with not problem.

 

[racerone]

I can not see or hear your motor.-----But the motor speeding up tells me it is running out of fuel.-----In my opinion this is an easy fix.-----Could also be a bad reed valve causing low crankcase compression.-----The + crankcase PRESSURE pulse drives the fuel pump.

 

[Crosbyman]

depending on the fuel hose you have .....you have a single or two ended connector hose

in the mean time .....
to stop suction air leaks try a few wraps of cellophane and tape around one end (ex: motor side) end ..... see if problem clears up
then try the other end and do the same test
if the issue clears up you found the bad hose junction

btw those little square pumps have been known to be faulty
try your old pump just in case

and do a blow test on the " new" one
Air in to out OK if air passes one way only
Air out to in ....should not pass

inlet needle could be sticky... did you you a blow test on the carb and did you install the little pull down clip on the inlet needle

did you do a full carb job by inspecting the idle drip chamber (2-3 very small holes) and blowing the side channel with carb cleaner and air pressure.
That side channel leading up to the idle cct. is very narrow. so make certain carb cleaner shoots up the top side when you inject the cleaner in the side channel otherwise the idle cct may starve.

 

[Four22]

New fuel line procured. Hopefully try it out this evening and see what happens….

 

[Four22]

Problem solved. Ran for an hour and a half in the driveway tonight. Now it’s time for a test ride!

Thanks all!!

 

[Crosbyman]

so it was the hose ? what was wrong with the old hose.....leaky seal o-rings?

 

[Four22]

Not 100% sure honestly. I know for sure one if the bulbs I had was bad. And judging by how loose the old connectors were, I’d say there was leak at an o-ring.

I opted for a complete fuel hose with crimp clamps on it trying to eliminate as many variables as possible

 

[Four22]

One more question….. where does the roller for the throttle go in relation to the 2 marks on the timing advance?

When the roller is between the 2 marks, should the butterfly be just starting to open?

I’ve dug around and can’t find the exact adjustment

 

[Crosbyman]

see picture isthis what you are referring to ?? this is an older engine but same principle

 

[Four22]

That’s what I’m looking for but there’s 2 marks on the cam. Does roller go between the marks, on the first or on the second?

 

[Crosbyman]

center it between and try it.... if not OK readjust...the marks can't be that far apart

 

[F_R]

Agreed. Those things are virtually impossible to get so precise. I suppose that's why they gave two marks.

 

[Four22]

Well… got the motor out last week on the lake. Ran fine all morning. Started up first or second pull.

On the last leg in, the dang thing would barely run. I hely it wide open but it only ran about 1/2 of max rpm. Not sure what’s going on and haven’t torn into it yet….

On top of that, broke the recoil start spring and spun the prop. Was quite the shot show of a day