1970 4 hp stops after running a while on high speed.

[Don Hansen]

I have a 1970 Evinrude 4 hp that shuts down after running for a while, maybe 5 to 10 minutes, at full throttle. It acts like the throttle is, over maybe a 5 second period, being turned down until it just stops. Squeezing the bulb while it's doing this does not help and I run my 35 hp from the same tank with no problem. It will run at trolling speed for hours with no problem. I took a look at the water pump and although it is worn all the fingers are there and they are pliable. I feel no restriction when I blow through the water tube. I've seen it mentioned here that if a motor has been over heated you can see signs of it in the paint around the head area. I see nothing like that.

Here are my questions. If a motor overheats will it shut down like I described? If I use one of those infrared thermometers on the head what would be a normal temperature? Is it possible that it is fuel related, the fuel pump or maybe the carb, and that squeezing the bulb will not override it?

Don H

 

[Rick.]

Re: 1970 4 hp stops after running a while on high speed.

I would do some basic stuff first. Check for spark on both plug wires. Pump your bulb real solid and check for fuel leaks. A fuel leak at high throttle may show up more than one at slow or trolling speed. If your thinking your pump is the culprit you can disconnect the line at the carb. and give the recoil some pulls to see if it is delivering gas. Best of luck. Rick.

 

[Don Hansen]

Re: 1970 4 hp stops after running a while on high speed.

Is it possible for a motor to overheat and not show signs of it in the paint around the head. For a motor to get so hot it stops it must really be hot, right.

Don H

 

[lindy46]

Re: 1970 4 hp stops after running a while on high speed.

Is it pumping water? - a mist/spray coming out the holes in the mid-section? If you let it cool down for a while, does it re-start ok and run ok at high speed?

 

[Rick.]

Re: 1970 4 hp stops after running a while on high speed.

Is it possible for a motor to overheat and not show signs of it in the paint around the head. For a motor to get so hot it stops it must really be hot, right.

Don H

Yes it is actually. Post above is right on with checking your pump if you suspect an overheat. Rick.

 

[nwcove]

Re: 1970 4 hp stops after running a while on high speed.

why would you go through the trouble of removing the impeller for inspection and not replace it?? its one of the cheapest parts, but so important. i recently did some work on a 6hp,it was pumping, but weakly, pulled the impeller...it looked like new, but the motor was stored for five or six years, replaced the impeller, and it the change was more than obvious.

 

[Don Hansen]

Re: 1970 4 hp stops after running a while on high speed.

I did a post about an hour ago and it seems to have gone to never never land.

I was planning on changing the impeller just to be sure. I think while I'm at it, I'll change both coils. Makes sense that the coils would run hotter at full throttle, maybe one of them is breaking down. I've had the motor since 1976 and the coils have always been the biggest problem area.

Over all it's been a good motor. If I could buy one like it today I wouldn't think twice.

Don H

 

[Rick.]

Re: 1970 4 hp stops after running a while on high speed.

71 was a much better vintage. LOL. That's what mine is. If you have replaced the coils once at lease I would not be too sure doing it a second time is the answer. I've heard the second generation of coils were better but can't say for sure. What I would do is take you spark gap tester on the boat with you. Check for spark when it acts up, not when it's running well. My opinion anyway. Rick.

 

[Don Hansen]

Re: 1970 4 hp stops after running a while on high speed.

Bad news. Looks like I found the problem. Looking through the sparkplug holes I can see that the lower cylinder connecting rod has a LOT of play in it when moving the flywheel back and forth at TDC.

I really would like to fix the motor. What are my options. Are the parts available to rebuild it. Does anyone have rebuilt power heads or maybe good used ones available for a motor that age?

Don H

 

[Rick.]

Re: 1970 4 hp stops after running a while on high speed.

That's too bad Don. No one wanted to hear this news. At the start of this forum in the top secret file there is a post giving the names of many businesses that could help you out with used parts perhaps. Go easy as unless it has sentimental value new internal parts might be cost prohibitive. Wish you (and your engine) well. Rick.

 

[hidef]

Re: 1970 4 hp stops after running a while on high speed.

The four horse uses bushings the only bearings are at the top of the engine. If you are lucky you might get away with just replacing the bushings.