Logo

65 Johnson 18hp won't stay running

Cable

Member
Hopefully someone here can point me where to look for this.

This was my grandfather's motor. It sat on a stand in his basement for many years. Never got used much. 5 or 6 years ago, my dad and I rebuilt the carb and had it running great. We ran it totally out of gas and it's been back on the stand ever since.

Now I'd like to use it. It starts easily and runs good for a couple minutes then tapers off and dies once it warms up a little. It will restart but only for a few seconds. I've tried moving the choke to every point, tried adjusting the rich/lean knob through the whole range, tried giving it a little shot of starting fluid and made sure carb to intake nuts are tight. No change. Tried giving it more throttle once it starts tapering off. The only thing that makes a difference is letting the motor go back to a cold state, then it will run fine for a couple minutes again.

Can someone please give me a little guidance with this?
 
<p>
Step # 1 is to post compression test results.---Always a must in trouble shooting.-----Have coils ever been replaced ?-----Next is to see if spark will jump a gap of at least 1/4" on a test device or set-up.----Does motor keep running if you operate the manual pump ?-----Have you installed a new water pump impeller ?-----With a little common sense and care you will have a great motor.-----Easy to repair and parts are everywhere in my opinion.</p>
 
Last edited:
Thermostat in place and working properly?----Running in a test bucket with water at least 6" above the water pump ?
 
<p>
Step # 1 is to post compression test results.---Always a must in trouble shooting.-----Have coils ever been replaced ?-----Next is to see if spark will jump a gap of at least 1/4" on a test device or set-up.----Does motor keep running if you operate the manual pump ?-----Have you installed a new water pump impeller ?-----With a little common sense and care you will have a great motor.-----Easy to repair and parts are everywhere in my opinion.</p>

Haven't tried compression test yet because while it's running, it's running great. What is ideal compression? Pumping the ball doesn't help. Replaced impeller when we got it running a few years ago and it seems to be spitting good. Don't know about the coils.
 
Thermostat in place and working properly?----Running in a test bucket with water at least 6" above the water pump ?

Water is over 6 inches above pump. Don't know about thermostat. There's 2 little covers on motor. 1 is on the head and the other is on block above fuel pump. Which one is the thermostat?
 
The coils can start to fail once they warm up a little? It runs like it's new when it's cold. I can give it more gas and it revs up like it should. Good throttle response. Once the rpms begin to drop, I can give it more gas and it will keep running but after about 5 minutes it dies even with the throttle all the way open.

Is there a way to test the coils with a multimeter?
 
I suggest you pull the flywheel.-----Easy with a puller using the 3 holes.-----Inspect the coils.-----Clean and set the breaker points.-----Replace condensers.--------You need to do this to get an easy to start smooth running motor.-----Then again we can not see / feel or hear your motor.------fdrgator and myself can repair your motor without the use of a manual.-----Likely have each and every part for it on hand too.------Maybe test running with anoother tank and hose is what you need to do.
 
racerone and I have both seen hundreds of them like this. But we haven't seen yours.
 

Attachments

  • Cracked coils2.jpg
    Cracked coils2.jpg
    67.8 KB · Views: 21
Sticking carb float, Unscrew the high speed plug in the lower bowl front, squeeze the bulb until fuel starts to pour out, if it dosen't, there's your sign! Put the plug back in. Squeeze the bulb till it's hard, pull the choke and light it off.
 
Hey guys. Been under the weather for a couple days but feeling better and trying to pull my flywheel. I got 2 of the 3 short screws out which is where I'm supposed to attach the puller? That last one won't come out with my impact. Is it OK to use a puller with the 3 claws that hook under the outside rim? This is not electric start so I'm not terribly worried about the gear.
 
The only port on the lower front carb is the place where the rod from my rich/lean knob attaches. If that's the spot you're talking about, I'm not sure how to get the rod out of there. Don't want to fumble around and break something. Any tips?
 
Hey guys. Been under the weather for a couple days but feeling better and trying to pull my flywheel. I got 2 of the 3 short screws out which is where I'm supposed to attach the puller? That last one won't come out with my impact. Is it OK to use a puller with the 3 claws that hook under the outside rim? This is not electric start so I'm not terribly worried about the gear.


NO! That is a great way to break the flywheel
 
You remove the plastic bits from the rod on the carburetor bowl.-----Then remove the rod / plug from the bowl.----Then perhaps remove the high speed jet ( orificeplug ) found in there.----Carburetor on a 2 stroke must be clean----Best to remove the carburetor for cleaning.----Lots of helpers for you on you-tube.----Also go to school on -----leroysramblings----The 18 is nothing but a bigger 10 HP.----All easy to work on.
 
NO! That is a great way to break the flywheel

Ok &#55357;&#56862; that's bad news. Not sure how I'll get that last screw out then. Already chewed up the slot on the screw a little bit. I might have to drill it out. Are those screws just there to keep the threads clean? It doesn't look like they are actually holding anything together.
 
You remove the plastic bits from the rod on the carburetor bowl.-----Then remove the rod / plug from the bowl.----Then perhaps remove the high speed jet ( orificeplug ) found in there.----Carburetor on a 2 stroke must be clean----Best to remove the carburetor for cleaning.----Lots of helpers for you on you-tube.----Also go to school on -----leroysramblings----The 18 is nothing but a bigger 10 HP.----All easy to work on.

Thanks. I'll look around on YouTube tonight to see if I can learn some tricks.
 
racerone and I have both seen hundreds of them like this. But we haven't seen yours.

Ok. Got the flywheel off. Everything under there looks very clean. Unknown how old these components are but as I originally said, this motor sat on a stand the majority of its life.
 
Trying to upload photo

Ok. Doesn't seem to be working but everything under there basically looks new. No corrosion at all. Can the coil and condenser be checked with a multimeter?
 
Last edited:
Make sure you clean up those metal filings sitting on the lamination of the left hand coil.
Maybe it’s just grease, but have a close look at the left set of points. Where the little rub block, that is actioned by the lobe on the cam, it looks to be burned and/or some metal missing.
 
Make sure you clean up those metal filings sitting on the lamination of the left hand coil.
Maybe it’s just grease, but have a close look at the left set of points. Where the little rub block, that is actioned by the lobe on the cam, it looks to be burned and/or some metal missing.

Good eye! It was some metal pieces. Flywheel didn't come off easy. I blew the whole thing out with the airhose

And the dark stuff is grease
 
I was sure I nailed it with the cracked coils diagnosis. Obviously, I was wrong. Sorry 'bout that.
Ok so it's time to start back at the beginning. You need to troubleshoot when the problem exists. That is when the motor slows and quits. Surely, you have 50-1 fuel/oil mix, right? Is it overheated? Is there gas in the carb? Is there water in the gas? I assume it must still have compression. Is there water ingestion into the cylinders? After seeing your pictures, I doubt it is an ignition problem. So much for my guesses.
 
I was sure I nailed it with the cracked coils diagnosis. Obviously, I was wrong. Sorry 'bout that.
Ok so it's time to start back at the beginning. You need to troubleshoot when the problem exists. That is when the motor slows and quits. Surely, you have 50-1 fuel/oil mix, right? Is it overheated? Is there gas in the carb? Is there water in the gas? I assume it must still have compression. Is there water ingestion into the cylinders? After seeing your pictures, I doubt it is an ignition problem. So much for my guesses.

Ya, no worries. It was a good idea to inspect the ignition area regardless. Gas is new, unlikely it has water in it. Compression is 105. Doesn't run long enough to overheat. Water gets mildly warm. I'm using 40:1 right now because it's been sitting dry so long and it originally called for 32:1. I plan to use 50:1 as my normal mix once it's running. Water in cylinders seems unlikely since the plugs aren't getting fouled and it runs great whenever cold.

I'm buying some new fuel line today. Replacing everything in the motor and will clean out the pump and carb. There's not really anything else that could be causing the problem as far as I can see.
 
Back
Top