70's 25HP Evinrude woes

[Wrfkaratemonkey]

Hey guys!

i finally got my boat floor all replaced and I thought I was good to go. The outboard gave me some trouble after sitting for two years, but once I replaced the primer bulb and fuel pump she fired right up. I also replaced the fuel lines and cleaned up the spark plugs which looked fine anyway.

So so I filled up a trash can and it ran fine. It started strong, idled strong, went through the throttle range in gear fine. Good to go right?

yesterday we put her in the lake for the first time. It fired right up, reversed away from the dock, shifted into forward and throttled up. Everything was fine for about five minutes when all of a sudden the engine died. It started right back up but even in neutral with the throttle lever down it would start and immediately max out in RPM. She was just screaming. I took the cover off and saw that the fuel pump was leaking because the new fuel pump had failed. The screw for the filter / inlet cover has stripped out. So we ran the trolling motor all day.

Today i I replaced the fuel pump. Again. The motor will start but only if I push the throttle lever up a little. At first the engine was starting and going straight to max RPM. I thought maybe it was because this motor still has the tiller handle on it (previous owner added the forward control setup and left the tiller on) and maybe it was stuck. So I turned that a few times and that problem went away. Now, however, the idle is rough. Sometimes it will idle for several minutes, sometimes it dies in seconds. The fuel supply does not appear to be having any issues.

When end I put it in gear and give it some throttle it struggles and dies. I've included a video. I'm just looking for some advice before I start tearing into things.

https://youtu.be/P5uBD7NvKs0

 

[Wrfkaratemonkey]

Just a note, in the video I put it into gear and then throttled it down instead of up. I did that knowing the engine would stall. The hose came out of the trash can again and the tarp was blocking the kill switch so I just stalled it out.

 

[racerone]

Sounds like it is running on just 1 cylinder.

 

[Wrfkaratemonkey]

I had not considered that as a possibility, thanks for that idea. When I get home from work I'll start it up and pull the top plug wire off then the bottom and see what happens.

 

[Wrfkaratemonkey]

Both cylinders are firing with good spark. Today it's hard to get it going and when it does it only idles for a short while. Can't throttle up. Going to pull the carb off.

 

[oldboat1]

Disassemble it (leave linkage springs in place). Soak carb top and bottom in your favorite cleaner -- I use lacquer thinner. Finish with carb spray in every opening. Probe with soft wire. Take off the domed fitting on top before soaking, and remove idle mix needle.

 

[Wrfkaratemonkey]

I completely tore the carb apart and cleaned it. It was shockingly clean to begin with. No blockage or build up, float operating as it should etc etc etc. Put it all back together and it won't fire up.

With starting fluid it'll fire up and run until that's gone. Primer bulb is firm and stays that way. Coils tested good. New spark plugs. Clean carb. New primer bulb and lines. I'm honestly a little lost on this one.

 

[Daviet]

Could you post a model number so we know exactly what engine you are working on?

 

[oldboat1]

Check compression, and measure spark.

 

[Wrfkaratemonkey]

It's a 25502B. Compression is fine. Spark seems like it may be weak or unreliable but the plugs are new and the coils within spec so today I pulled the flywheel. Is this a coil on top by the points? I'm confused because I have two coils on the side where the plug wires are.

 

[jimmbo]

OMC switched from the High Tension system with two coils under the flywheel to the Low Tension system with one charge coil under the flywheel, and coils near the plugs in the early 70s. 2 sets of points are still used, and two magnets, of opposing polarity are in the flywheel. It does throw a lot of people expecting the old system.

 

[racerone]

Those breaker sets ( points ) need to be very clean.

 

[oldboat1]

Pull off plug boots one at a time when running and see how or if the motor reacts.

 

[Wrfkaratemonkey]

Pull off plug boots one at a time when running and see how or if the motor reacts.

When I did that the motor continued to run, barely, but didn't actually die due to being on either of the cylinders independently. I used a spark tester on both as well during the times I could keep it running for a minute and spark seemed erratic.

A friend has a 1999 Mercury 40HP ELPTO that has all of the controls and everything with it that runs perfect. The friend price is only a few hundred so I think I may just buy that and sell this 25HP to someone who wants to go through it and give it new life.

 

[tootallofwa]

Did you syncronize the throttle with the spark advance? sounds like the linkage may be misadjusted to me.

 

[jimmbo]

You never mentioned whether or not you adjusted the Low Speed mixture needle. The initial 1 1/2 turns out is usually too rich for best/smoothest operation. A ruptured Fuel Pump Diaphragm can cause rough running too