Need help on next steps for 1971 4.hp. Evinrude

[chopper72]

Motor became increasingly hard to start. Finally started running at about half power, half RPMs, but would surge from time to time never reaching full power. I thoroughly cleaned the carb and it runs the same. What next steps would you take? Thanks. Carb cleaning is about as far as I have gone with a motor but would like to learn how to do more and it looks like this is my chance.

 

[racerone]

Wish I had a one $ bill for every time I read " cleaned the carburetor , still runs the same "-----The head gaskets are not a " premium " construction so do a compression test......And test the spark properly.----------Spark must jump a gap of 1/4" or more, does it, ---yes or no ??

 

[Vic.S]

Sound like its might be firing on only one cylinder so also do a cylinder drop test.If it confirms that swap plugs over to recheck for defective plug

Plugs are Champion J6C gapped at 0.030"

 

[tomhath]

What next steps would you take?

It takes three things to run: Fuel, compression, and spark. As already suggested, start by checking compression because without that you'll never get it to run.

Then check the spark. Most likely you have a weak spark on one cylinder and none on the other, but see what you have first. Probably need to go through the entire ignition system (points, condensers, coils, wires, and plugs) - a weak spark won't do the job.

You might also need a fuel pump but get good compression and good spark first.

That's a good motor, it's worth doing a full tune-up.

 

[rolmops]

These little engines do not have a needle bearing between the piston rods and the crank shaft. because of that they must be run with a 1:24 mix (you might get away with 1:32 ) If you use a 1:50 mix they will run but at the same time they will go bad fast. The richer mix will also increase compression (just a little bit)

 

[racerone]

???---The 4th thing that a 2 stroke needs in order to run is CRANKCASE COMPRESSION----That appears to be missed by many folks when trouble shooting the well made motors.

 

[chopper72]

This is really helpful. I know how to clean a carb so when all you have is a hammer all the world is a nail. This problem is making me extend my knowledge. I pulled the plugs and one was dark and had a nice oil residue on it. The other was dry at the tip and the base was dry too. I am away from home and didn't have anyone to help so I was able to see that both plugs have a blue spark but I could not see if they could jump a quarter of an inch. There is oil residue around the head gasket. Does that point to a bad gasket or is that normal?

 

[Don Hansen]

Check the spark plug wires where they go in the boot. Make sure the copper wire is making contact with the clip. If that's not it then I'm betting on a bad coil. Those are the 2 things that have mostly gone wrong on my 1970 4 hp and I've had it for 41 years. I would do a complete tuneup, points, condensers, and both coils while I had the flywheel off. Having said that I did have to rebuild the 4 hp 3 years ago but its probably got 3 times the hours that my 35 has because I use the 4 hp as a kicker .

 

[Tim Frank]

Wish I had a one $ bill for every time I read " cleaned the carburetor , still runs the same "-----The head gaskets are not a " premium " construction so do a compression test......And test the spark properly.----------Spark must jump a gap of 1/4" or more, does it, ---yes or no ??

^^^^ that was post #2.
We are now at post #8 and climbing.
Until the OP actually acts on Racerone's questions we are all just wasting our time and the OP's by guessing.
If he does those checks, he'll be within sight of the problem AND the solution.

Otherwise it is just "even a blind squirrel may find a nut".

 

[Tim Frank]

These little engines do not have a needle bearing between the piston rods and the crank shaft. because of that they must be run with a 1:24 mix (you might get away with 1:32 ) If you use a 1:50 mix they will run but at the same time they will go bad fast. The richer mix will also increase compression (just a little bit)

???? How so?

 

[rolmops]

???? How so?

carbon build up and the fuel is just a wee bit stickier.

 

[chopper72]

Alright it has taken me a while. The compression is fine. The carb is clean. It has spark, and it appears blue at the spark plug but it still runs poorly. It misses more when it is under a load and running at slower speeds. I have not pulled the flywheel off yet. Should I go ahead with points and coils? Fuel pump? Thanks again

 

[racerone]

Sorry, but you can not test for good spark using a sparkplug.

 

[oldboat1]

I'm hearing you say that you checked the compression cold with a screw in tester, and got 90 lbs on top and 88 on the bottom. You completely disassembled the carb and soaked it overnight in solvent, then used a wire to clean every port, sprayed it with compressed air, put in a carb kit with a new expansion plug and reset the low speed needle. You readjusted the needle when operating to obtain the best idle you could. Then you used an adjustable spark tester, and got 3/8" spark on both cylinders. You pulled off the plug wire on the top cylinder while running, and the engine stumbled. You pulled off the bottom plug boot, and the engine wanted to stall.

But you still have operating issues.

Because you have excellent spark and you are not dropping a cylinder, you do not need to pull the flywheel for ignition work.

That leaves the fuel pump. You can check output by pulling off the fuel line at the carb. If in doubt, you should obtain a rebuild kit, or go ahead and replace it.

If I have any of the troubleshooting and repair history wrong, you should correct me.

 

[rolmops]

How about link and sinc?

 

[fhhuber]

A fouled plug can look like it has good spark when not installed in the engine, but still not function when installed. Since one looks oily I'd change plugs. A fouled plug can have most of the spark energy flowing through the buildup on the insulator instead of jumping the gap. This just keeps getting worse until you have that cylinder failing to fire. (even though the test for spark jumping a large gap passes)

Compare the old plugs to a chart of what the colors mean
such as this:

(Deposits pic would mean wrong oil in our 2-strokes)

Once you have tested that... realize that while this might get it operating OK immediately, there is some reason that one plug fouled and the other didn't and you need to figure that out. It could be as simple as the insulation on the plug wires degrading from age and one failing before the other. There might be a carb imbalance, reed valve issue (if its a reed valve engine) or several other issues.

 

[chopper72]

I disassembled the carb and soaked it. I installed a new carb kit. The compression was in the mid 80's on both cylinders. I put in new spark plugs. I have not tested the spark other than to see that it is blue. What do I need to do to test spark properly? Thanks for your help.

 

[oldboat1]

You need to get an adjustable spark tester, available at auto stores for ten or fifteen bucks. Test with both plugs pulled. I start at about a half inch, and work back looking for spark. 1/4 inch is considered adequate for operation. Additionally, you may be losing spark during operation ("dropping a cylinder"). You check that by carefully pulling off plug boots, one at a time, and check response. If no change, that cylinder is not firing. (The motor can run on one cylinder.) If you have inadequate or sporadic spark, you need to troubleshoot. (Start with the connectors at the plug boots.) At this point, you would normally pull the flywheel: check for cracking coils (replace), or dirty points (clean and reset). You may end up replacing coils, points, condensers and wires.

all standard stuff. Question as you go. Also try the "link and sync" suggested above -- adjusting to insure the throttle and carb are synchronized (a sticky or two on this procedure).

It's also common to go back into a carb if there is any doubt about cleaning or condition (your call, as you did a rebuild). There is also the potential for fuel pump rebuilding or replacement, as was mentioned above.

But get a tester and check the spark.