Johnson 18hp won't stay running.

boatsalotjay

Petty Officer 2nd Class
Joined
Mar 28, 2004
Messages
110
Hi Everyone,<br /><br /> I recently bought a 1957 18hp M#FD-11. Excellent looking little motor, looks to be hardly used. The guy said it ran like a racehorse. Well, I put 'er in the barrel and tried starting it up and it will fire nicely and run for about a second and die. I am stumped on this one, both spark plugs are firing, pressure tank is getting plently of gas to the carb, I can't think of anything else that is wrong. It did run for a good ten seconds one of the first times I started it, but that was all I could get out of it. Any ideas? Could a crack in a gas line be sucking air possibly? Any help would be appreciated. Thanks!
 

Paul Moir

Admiral
Joined
Nov 5, 2002
Messages
6,847
Re: Johnson 18hp won't stay running.

If it only runs for a second, it's not the pressure system since there's enough fuel in the carb's bowl to keep it idling for much longer than that. A crack in a pressure system fuel line will let fuel out rather than air in afterall. But, is the tank holding pressure? <br /><br />Make sure you can draw a spark 1/4" long or longer off each spark plug lead, just a spark plug gap can hide problems. Try adjusting the carb a bit to see if it helps.
 

Timbertim

Seaman Apprentice
Joined
Apr 1, 2005
Messages
44
Re: Johnson 18hp won't stay running.

I just went threw a lot of this yessterday on this site. My problem was a plugged jet. Clean the carb out good. I cleaned mine and it works now. See if it will run while you sqirt mixed gas into the carb throat.
 

Paul Moir

Admiral
Joined
Nov 5, 2002
Messages
6,847
Re: Johnson 18hp won't stay running.

Definitely a good idea! The windex-type bottle full of pre-mix is one of the handiest tools for diagnosing an outboard.
 

boatsalotjay

Petty Officer 2nd Class
Joined
Mar 28, 2004
Messages
110
Re: Johnson 18hp won't stay running.

Yes, the tank is holding pressure. This is my first motor with a pressure tank, are they a real pain sometimes?<br /> <br />I will take a look at the carb tommorrow. Plugged jet sounds like definite possibility I should have thought of. By a 1/4" spark do you mean hold the plug that far from a ground, or ??? I guess I will check the gap also, didn't know spark could cause that much trouble. My arm is feeling all that pulling right now though, so I guess it can. :)
 

Paul Moir

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Joined
Nov 5, 2002
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6,847
Re: Johnson 18hp won't stay running.

Yeah exactly - 1/4" or more to ground. You can rig up a gap by nailing a couple nails into a board, and connect one to ground and the other to the spark plug lead. It's tough to try holding a spark plug and pull the engine over. :) Oh, and you don't need the spark plugs in for this test. <br />I seem to get those sort of symptoms sometimes when the (cracked from age) coils arc over as the rpms pick up. It's a pretty common problem with these vintage J/E 2 cylinder engines. As soon as you get the flywheel nut torques I strongly suggest pulling the flywheels of the two little motors and giving them a visual check. <br />But ASA VET has a good point - you can get that same sort of symptom from a fouled carb. <br /><br />As for the pressure tank, they are rarely a problem at all. Sometimes the connectors leak, but you can rebuild them easily.
 

BoatBuoy

Rear Admiral
Joined
May 29, 2004
Messages
4,856
Re: Johnson 18hp won't stay running.

Biggest problem I had with that fuel system was ruptured pressure hoses, both the one from the tank to engine and the ones internal. When I say ruptured I mean a leak which sprays a needle-size stream until tank pressure is released. Now that I think back, this happened pretty frequently and I wonder if I was getting aged hose from the dealer I was using.
 

boatsalotjay

Petty Officer 2nd Class
Joined
Mar 28, 2004
Messages
110
Re: Johnson 18hp won't stay running.

Well, I took the carb off today. The float looked terrible, am ordering a new one. The local mechanic who I order my parts through said it doesn't sound like a float problem. He said it could be a lower seal too. Didn't get around to the spark test. Will do that tommorrow. <br /><br />Wanted to say thanks to you all for your help (ecspecially Paul and JB) I managed to get my 3hp going without much trouble using all the info you guys have given. Feels good to get a motor running when someone sells it to you for nothing saying it doesn't run and doing a little work on it to get it purring again. Its a great little runnner.
 

hornlake

Cadet
Joined
Oct 22, 2004
Messages
12
Re: Johnson 18hp won't stay running.

If you have a glass bowl at the base of the carb unscrew and remove the metal fuel filter. Now try and start your motor. <br /><br />I had a similar experience with my 1958 10 hp Sportwin and a plugged fuel filter from sitting was the problem. FYI I tried soaking in cleaners without success and ending up replacing.
 

boatsalotjay

Petty Officer 2nd Class
Joined
Mar 28, 2004
Messages
110
Re: Johnson 18hp won't stay running.

Well, I tried the spark out today. Not getting much. Seems like a very weak spark. Every time I pulled the cord I was getting gas spraying out the spark plug holes so I don't think its a gas problem, is that right? Now it doesn't really want to even fire, I looked through the inspection hole and the coils look fine, they aren't the old fiberglass ones that can crack. I will clean up the points with my dad's help tommorrow and see what he thinks also. If I pull the flywheel do I have to be careful of certain things? I've done it before on various motors, and had trouble with one after that (I had trouble with it before that too, but I didn't get the flywheel on tight enough after that I think, it was a '58 35hp Seahorse btw.) Is there anything special I should know? Thanks. <br /><br />Thanks for the reply also, Spooner.
 

Paul Moir

Admiral
Joined
Nov 5, 2002
Messages
6,847
Re: Johnson 18hp won't stay running.

It'll look just like the 35hp - it's pretty much the same thing. Except the flywheel will be a lot easier to get off and back on again.<br />Even the modern ones are suceptible to cracking. They don't open up large gashes like the really old ones - just little spider-cracks. But it sounds to me like cleaning up the points and setting the timing may be enough. If there's a coating of oil on things, the top seal is gone and will need to be replaced.
 

boatsalotjay

Petty Officer 2nd Class
Joined
Mar 28, 2004
Messages
110
Re: Johnson 18hp won't stay running.

Thought I would let anyone who cares know that I pulled the flywheel, set the points and it now runs great. Thanks for all your help guys! Couldn't have done it without you.
 

BoatBuoy

Rear Admiral
Joined
May 29, 2004
Messages
4,856
Re: Johnson 18hp won't stay running.

Glad you got it running. Also glad you came back to report. Too many come here to get advise and are never heard from again. Again congrats. Hope your fishing trips are productive.
 
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