1976 40hp Evinrude fouling 1 spark plug

[mikear]

The motor will start and run/idle rough at ~1/4 throttle. Boat will plane out and run for ~1 minute then it will start to surge and lose power. It will eventually stay at a power loss occassionally surging for a second or two at a time. The top spark plug fouls and the bottom plug looks good. Plugs have been changed many times (autolite 4092). The recommended Champion UL81C have also been tried but wouldn't work at all.

The ignition coils have been changed. Spark will bridge 7/16"-1/2" gap with either coil. Compression is at 107 psi per cylinder (equal). After motor surges and the plugs are pulled the top one will be fouled. Carb has been cleaned and the fuel pump was also changed. I am at a loss.

I haven't checked the points, etc., however I am not sure why spark would be seemingly good and have a problem with the points. Please help.

[mikear]

Also, there is a problem with the armature plate. Sometimes it will not retract fully when throttling down to allow the gearcase to be put in neutral. Not sure if this is relevant to the issue.

Thanks.

[Lion hunter]

I would check the points. Did you replace all the hoses and filters from tank to carb? Sounds like an air leak to me. Can you pump the bulb and keep it from doing it?

[mikear]

I would check the points. Did you replace all the hoses and filters from tank to carb? Sounds like an air leak to me. Can you pump the bulb and keep it from doing it?

If I pump the bulb It does nothing. I have not changed the fuel return (terminology?) lines. The fuel line, bulb, fuel pump screen have all been changed. I had an inline fuel filter in addition but removed it to see if that was part of the issue. I will replace the return hoses, anything else I'm missing?

Are there any tricks to removing the flywheel other than a flywheel puller? I have a couple of ideas but I don't want to spend a lot of time on something when there's an easier way. Is there anything else I need to check while I have the flywheel removed?

Thanks.

[Lion hunter]

A puller is the best method. I use a harmonic balancer puller (turkey foot) and you can borrow them from autozone if needed. Use high grade bolts!

[mikear]

I pulled the flywheel today and checked the points. The cylinder that was fouling the plugs had the points pitted/corroded pretty bad. I ordered an OMC ignition tune up kit (2 condensers/capacitors and 2 points). The good cylinder's points are as smooth as glass. The points are about 0.025" vs. recommended 0.020" gap. I took 220 grid and cleaned the pitted set. I am going to re-gap them tomorrow and try to take the boat out for a test this weekend.

I also purchased new fuel return lines and the other hoses that haven't been replaced previously. We'll see if it clears up at all. I will check the capacitance/resistance of the existing condensers as well. I'm not sure of the equipment needed to do the leakage test.

I will update the post once I test it out.

Thanks.

[1946Zephyr]

I would also try the J6C Champions in that motor too. Hopefully, replacing the points will cure your fouling issue. If you find that you have a weak spark, then you could have a bad connection in your spark plug lead, either at the coil, or at the spark plug boot.

[mikear]

I would also try the J6C Champions in that motor too. Hopefully, replacing the points will cure your fouling issue. If you find that you have a weak spark, then you could have a bad connection in your spark plug lead, either at the coil, or at the spark plug boot.

I'm thinking it's either a weak or missing spark, only when warm, since it only happens once the motor seems to warm up. I've checked and replaced the spark plug leads, boots, and plug terminals. Are the J6C a replacement for the old UL81C?

Thanks.

[mikear]

Finally got some time this weekend to mess around with the motor. I replaced the lines and hoses that I had not previously replaced (don't think this was the issue but it needed to be done). I also put a final polish on the set of points going to cylinder that had been fouling the plugs. I gapped both sets of points to the recommended .020". I then performed a link and sync.

Took the boat out to the lake on Sunday and it idled much smoother than before. I was very excited to see the difference and mashed the throttle after exiting the no-wake zone. After passing 1/2 throttle, or when the cam follower leaves the armature plate and begins opening the throttle valve, it promptly died. I thought about it for a moment. It suddenly dawned on me (DUH!) that after owning the boat/motor for ~9 months with it never running correctly, I had adjusted the carb to it running on the one cylinder. After a short run with a buddy steering the boat I was able to adjust the carb and it took off like a scalded cat.

You want to talk about excited, I could almost see my smile in the wake!

Now just to find out if both of my props are spinning on the hub or not. At least one time each, the boat stopped moving forward and the motor revved to very high RPMs when rappidly increasing the throttle from idle. Once throttling down and slowly increasing the throttle it would take off just fine.

Thanks to those who commented for the advice. This site is truly a great reference/resource for those do-it-yourselfers out there. I am just glad I didn't take the boat to the somewhat-local outboard mechanic for $99/hour. I ended up spending <$15 for the hoses and the sandpaper for cleaning up the points was free! Just took an afternoon, the service manual, this site, and a little elbow grease to get the motor where it is now.