Johnson 15hp Problems!!

[Lovejoy]

I have a 15hp eltric start Johnson.I think an 88 model. . It will idol great in fact it will go for days and days. When I put into gear I can only run a 1/4 of the throtal. It's like it has no more power. It seems to smoke a little bit more also my plugs are geting very black. I have had the Carb cleaned, Replaced power pack, 3New sets of plugs and I have got no where.I think I may have a electrical problem some where but Not to familiar with boat motors. Could some one please help!!

 

[knownascrll]

Re: Johnson 15hp Problems!!

what are you mixing your gas to . 50:1 . sounds like your not mixing your gas to the right mixture. I had that problem with it not wanting to run hard to start. I changed the plugs , carb rebuilt, coil , new gas tank , rebuilt the fuel pump, new bulb an hose. male fuel connector . Come to find out i had the wrong femal connector for the fuel line. I had one for yamaha an i needed it for 15 horsepower evinrude

 

[tashasdaddy]

Re: Johnson 15hp Problems!!

Welcome to iboats. lets start with the basics, to troubleshoot this. get a screw in compression tester, remove plugs, insert tester, turn engine over 4-5 revolutions, record reading, then do the other cylinder, record. now do a spark test, on both. blueish spark jumps 1/2 inch. post these results. and we go from there. this tells use if you have a base problem, then we go from there. it is a step by step process, to find what is wrong.

 

[jacob lovejoy]

Re: Johnson 15hp Problems!!

I testesd both cylinders & they both were 80psi. I also tested the spark plugs to see the fire and they also looked ok to. The motor has a sticker on it saying 100:1. I have always mixed to those specs and never had a problem. What do you think I should mix to?

 

[Mr.Stuart]

Re: Johnson 15hp Problems!!

I have an 89 9.9 same power unit I think, and the mix on mine is 50 to 1

 

[jacob lovejoy]

Re: Johnson 15hp Problems!!

Welcome to iboats. lets start with the basics, to troubleshoot this. get a screw in compression tester, remove plugs, insert tester, turn engine over 4-5 revolutions, record reading, then do the other cylinder, record. now do a spark test, on both. blueish spark jumps 1/2 inch. post these results. and we go from there. this tells use if you have a base problem, then we go from there. it is a step by step process, to find what is wrong.

I tested both cylinders and they were both 80psi. I checked the plugs and I seem to have good fire.So what do I do from here??

 

[lexkyboater]

Re: Johnson 15hp Problems!!

Did you test fire just using plugs or did you use a tester? Do you have or can you make a spark tester? See http://forums.iboats.com/showthread.php?t=213548&highlight=spark+tester. Remove the plugs, attach the plug wires to tester and if you have a CDI ignition, not points, spark should jump 7/16+ inches. This is done to make sure you have adequate fire.

After you verify that, you can proceed to carb. Make sure the choke is not closed when running. Sounds like you might need a carb rebuild. How long has it been since that's been done? Most guys here recommend every 3 years or so if the motor has been in service. If you pump the fuel line bulb, does that help it run? If you pull the choke, does it run better or worse? Also, you might want to try adjusting your carb. See Joe's excellent post at http://forums.iboats.com/showthread.php?t=167352. You want to make sure the mixture is right at both idle and high speed. It looks like this model only lets you adjust slow speed mixture (high speed jet is fixed), but be aware that the slow speed mixture affects high speed too. If it runs rich at slow speeds, it's likely running rich at high speeds. It sounds like it's running rich per your symptoms, and that may either indicate adjustment or some clogged ports in your carb.

 

[F_R]

Re: Johnson 15hp Problems!!

Lack of power at high speed generally means it is running on only one cylinder. Can be caused by poor or no spark. Or spark plugs. Remove and ground one spark plug wire and see if it makes a difference. No difference? Then that one wasn't firing.

The 100:1 ratio was retracted. Supposed to be 50:1. However, if you are running at idle hour after hour, 100:1 might help. How about something in between?

 

[mikesea]

Re: Johnson 15hp Problems!!

make sure the timer base under the flywheel is advancing with the throttle,it will be connected to the throttle linkage,you might only be getting fuel and no spark advance

 

[Chinewalker]

Re: Johnson 15hp Problems!!

I agree with Frank - probably running on one cylinder. You may visibly have spark at the plugs, but I would try this test:
Start and warm up the motor. Shut it off. Remove one plug wire and attempt to restart the motor. If it starts and runs as before, then the one you removed is not firing. If it does not start at all, then the one still connected is not firing. Then work from there. You've already replaced the powerpack. Try swapping the coils top to bottom and see if the issue follows the coil...
- Scott

 

[lexkyboater]

Re: Johnson 15hp Problems!!

Another question - is it running so rich that it can't breathe or is running so rich that it's fouling plugs, which then causes it to run on one cylinder? Following Frank and Scott's advice to figure out which one is not firing is a start, but when you put in fresh plugs does that temporarily fix the problem? Another words, does it run good for a while till one of the plugs fouls? Why did you try 3 sets of plugs? Was one plug fouling every time? Have you owned the engine for a while, and this just recently started happening? It would be helpful to know what the spark jump is with the tester.

Another problem could be plug wires - if you check resistance from start to end and try wiggling them when your ohm meter is hooked up and see if there's an open circuit. They are many times overlooked when ignition components are replaced, but there's been several postings when that was either a problem or the problem when performance is an issue. My motor had a problem with a plug wire that had a weak spark and had an open circuit in it when wiggling the wire. When I say weak spark, it would jump the .030 gap on the spark plug, but with the tester I couldn't get it to jump any farther than 1/4 ", and even then it was a dull yellow spark. Nice blue spark jumped 5/16" after new plug wires and coils. But my motor has points, and shouldn't jump as far as a CDI ignition.

When you cleaned the carbs, were the core plugs removed? Did you just clean it, or did you rebuild it? I can tell you from recent experience and by other posters on this forum that those core plugs should be removed on a rebuild. See http://forums.iboats.com/showthread.php?t=213715 for some pics of a 71 Johnson 9.5 HP. I'm not ruling out carburetion yet, but it's going to be interesting to see what the problem is. Keep us posted!