1978 Johnson 15 hp

[daveys dingy]

My motor will start fine and run at a higher rpm but if shut down to idle it will stop in a very short time. Also notice at top speed, the speed varies, it will run fast for a while then will slow down. Is this in the carburator, or the fuel pump? Intitially I was getting bits of rubber from a deteriating hose, but changed that, and the last time I checked carb, it was clean, yet still have the problem. <br /><br />davey

 

[Bear]

Re: 1978 Johnson 15 hp

Hi Davey!<br />I think you still got parts of the hose in the carb.<br />Check these:<br /> CARBS 101 by 12Footer <br /><br />Maintaining Johnson/Evinrude 9.9 & 15 hp outboards <br /><br />Good luck!

 

[daveys dingy]

Re: 1978 Johnson 15 hp

As I said I have taken the carb apart twice now since the hose was replaced and it is clean. Unless one of the passages which are sealed is plugged. <br />Is there some place where you can buy a replacement (rebuilt) carb? like from OMC or a distributer of OMC?<br />What symptoms would I have if it were in the fuel pump?? <br />And thanks for the response!

 

[rickdb1boat]

Re: 1978 Johnson 15 hp

Davey,<br />As Bear said, I too believe you have a restriction in the Carb. Did you use Carb. cleaner and compressed air to blow out the passages when you serviced it? Does not sound like the fuel pump, as it will run at high RPM's and then stumble and die at idle. Try rebuilding it using a Carb. Kit and see what happens before you start looking for a new Carb. Generally there is nothing that can go wrong with a Carb. that a rebuild and thorough cleaning won't fix.<br /><br />EDIT: Check this link out, too!<br /><br /> web page

 

[Bear]

Re: 1978 Johnson 15 hp

Davey,<br />All I know about you and you experience concering small outboard carbs is from what I just read. "...and the last time I checked carb, it was clean...". To me it doesn't sound like a good and thorough cleaning. Maybe you did that the first time, at the same time as you replaced the rubber hose. You didn't say.<br /><br />So, 12footer explained it all, step by step. I saved the URL as it is great to include from time to time. The other link is very interesting if you got a 9.9-15HP OMC and don't know much about it. I know you didn't ask for it but sometimes it makes people happy to read, print and save it for later. <br /><br />All I say it is hard to know if you don't tell us. <br /><br />Tear the carb apart again. If it's clean it's clean, right? Follow Rick's advice. You can also check if the float moves freely, the float valve and the float valve seat.<br /><br />You can also look for an air leak from the tank and all the way to the carb gasket.<br /><br />But, you mentioned the rubber hose and I still think there is one very small piece of rubber left.<br /> fuelpump <br /> used carb, maybe <br /><br />Hope it helps

 

[daveys dingy]

Re: 1978 Johnson 15 hp

Hey guy's thanks for your help. I guess from what I'm reading you all think it's the carb and not the fuel pump, so I guess I will do the rebuild. Is there a good place (to order) to buy a rebuild kit?? My local OMC dealer went out of buisness. and thanks for the advice.

 

[ob]

Re: 1978 Johnson 15 hp

This place has a kit for 15.00 p/n 398453<br /> www.maxrules.com

 

[Jack Shellac]

Re: 1978 Johnson 15 hp

Bear: Thanks for that article on the 9.9 & 15 OMC's. It had some excellent information that I wish I'd had previously before starting work on mine over the years. A lot of it that the manuals don't mention, either.

 

[Boatist]

Re: 1978 Johnson 15 hp

Davey<br />I am going to give you one more idea. I have a 1975 15 HP Johson. I would suggest you hook up the muff and start it up with the cover off. Idel fast enough that it will keep running and pull off one spark plug at a time. I think you may have a fouled plug or weak spark on one cylinder. If they both have same effect when you pull off wires go back to your carb work. This happened to me and it turned out to be a bad coil for one of the cylinders. You can swap both input to coil and plug wires to find out if it is points or coil. <br />Mine also had carb problem. Float was set to high so it would flood at low rmps and die. Also cork float was tore up and deformed so did not always shut the gas off. Durning this time had lots of trouble with fouled plugs.<br />You will get to a solution quicker and cheaper if you trouble shoot logicaly. Both problems had the same symptons your motor does. Good luck and please come back and tell us what you find.

 

[daveys dingy]

Re: 1978 Johnson 15 hp

Hey guy's I will keep you informed as to what I find, but it won't be until I get to Florida (that's where I have the 15hp) as I just have too many things to get done and close up for the winter. I will be going down the first week of Jan. so will start on the project first thing. And thanks again for all the advice.