25 johnson help

C

Chris Riggs

Member
I've got a 72 25 hp johnson that for the most part it runs great and does just fine on my 14ft boat, but sometimes I can take it and it runs great and then leave it for a couple weeks and it will crank fine but half runs like its booging down and not getting all she has. I've rebuilt the carb and replace points coil and all it run fine all last summer and part of duck season , the the last weekend it started doing it again, I added an inline fuel filter, and rebuilt the carb again, I run it in a drum in the yard and seems fine haven't had time to put in the river yet. But what cause's that and how do I prevent it from happening agian? Any help would be appreciated.
 
39 year old motor designed to run on gas with lead in it? I dunno, maybe its a female motor in menopause.
 
Chris, My first thought was coils but since you replaced them I will need to think some more on this one. It probably is dropping one cylinder which eliminates the carb. Try to run it with a timing light or spark tester hooked up to see if you are losing spark. Points could be dirty. I'll keep thinking on this one.
 
You may have an air leak. I had this same motor and i found that if she has a pin hole in on of the vacuum tubes or the tank vent is not open enough, she will not run real well. Run NGK plugs,Champions are not well matched to your machine.
 
Ditto on the NGK's. Try pumping the primer bulb when it runs sour. You may have a failing fuel pump. NAPA sells kits for some of the pumps. Good Luck
 
With my 71 6hp rude. if I let it sit for 3-4 wks. I have ta change pluges or it runs like $h#t & hard starting. I'll have to try the NGK's this year, always run champs before. Try running some seafoam thru it, that smoothed out my 6 after a long storage period. Lee, a member here that passed away ,swore by seafoam& after trying it I'm a believer too. Good luck with it.
Dennis
 
I'm going with the air leak theory. Fuel lines are inexpensive to replace, and should be with some regularity - at least every five years or so. Nothing worse on a cold, freezing day than having a fuel line break.

On the off chance replacement does not do the trick, try squeezing your fuel bulb when it starts to bog down - if your engine gets up and goes as a result, you might be looking at a bad fuel pump. It's located on the side of the engine(gas hose going into and coming out of) and can be replaced with another - good news is that OMC 9.9 or 15hp engines use the same pump, and you can find them on eBay fairly often for less than $20. Easy repair that goes a long ways - even a new, used fuel pump is better than the one that's not working now.
 
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