J25 dies in H2O

[Marionboater]

I have a Johnson 25 that dies under load. Runs fine out of the water. I have:<br />*Put on new Fuel pump<br />*Cleaned carb (twice)<br />*Used another gas tanks/hose that I know works<br />*Verified that both cylinders are firing<br /><br />Any ideas???

 

[rwise]

Re: J25 dies in H2O

First welcome to Iboats.<br />second, have you ran a compression test? done a decarb? if you have ran a compression test post the results also.

 

[Marionboater]

Re: J25 dies in H2O

I have not done a compression test. Is that something I can do myself inexpensively? Is decarb the same as cleaning the carb? I took it apart, sprayed all ports and holes, and soaked it for a few hours. I did that twice.

 

[Brew2]

Re: J25 dies in H2O

Compression test is very simple....just need to buy/borrow a compression gauge. Not sure, but I would guess they are about $15 at any auto parts store. Basically the gauge screws into cylinder where the spark plug would normally go....you turn over the motor for 4-5 revolutions and look at the gauge to determine the reading. "Good" compression would be anything over 100 with both cylinders within 10% of each other.<br /><br />A decarb is not the same as cleaning your carb(s). Decarb involves purchasing some aerosol decarb solution and following the directions on the can to remove carbon build-up in your cylinders. Basically it involves spraying the solution into the carbs and therefore into your cylinders...waiting for a predetermined length of time for it to loosen up the carbon, then starting the motor to blow out the loose carbon. Kinda like oven cleaner cleans your oven. I think OMC calls their version of the decarb spray "Engine Tuner". Word of caution...don't do this around anything you want to keep clean...carbon and cleaner really make a mess of driveways, garage doors, etc. Here is a link to a description under the Engine FAQ section:<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=36;t=000016 <br /><br />Couple other thoughts:<br /><br />Check for air leaks in the fuel system...you could be sucking air under a load. All connections should be tight and the hose should be supple, not hard.<br /><br />You checked for spark, but did you confirm it was a strong spark? The spark should be able to jump a 1/2 inch gap and be bright blue. If you don't have a spark checker, you can purchase one from any auto parts place for $5.<br /><br />Good luck.

 

[Marionboater]

Re: J25 dies in H2O

Thanks! I will give your advice a try and report back.<br /><br />Will be a week or so, I'm out of town.

 

[fireman57]

Re: J25 dies in H2O

Have you verified that both cylinders are firing under a load?

 

[Marionboater]

Re: J25 dies in H2O

Fireman… how do I check under a load? To check before, I disconnected one plug and then started the motor. It started and ran OK. Then reconnected that one and disconnected the other and it ran too. Do I do the same thing under load? If it want do anything now with both connected under a load, how can I tell?

 

[BF]

Re: J25 dies in H2O

Hi,<br /><br />I'm not sure how new you are to outboards... but when you say "It runs fine out of the water", does that mean that you have run it without a water source? Or did you run it with a garden hose attached, or in a garbage can of water?<br /><br />The rubber impeller in the water pump will overheat and start melting within a few seconds if an outboard is started without a water source.<br /><br />When you run it in a garbage can or on a boat, does it pump water OK?<br /><br />As said, compression test would be good to do. What year of motor are you talking about? Yes, as fireman implies, sounds like you may be loosing a cylinder/spark under load (or when the motor heats up).

 

[Marionboater]

Re: J25 dies in H2O

Thanks BF. When I run it "out of the water" it is with a garden hose and the pump supplies a good, steady stream out of the engine.<br /><br />If we determine it is loosing spark, I guess I will have to ask the question, "how do I fix that"!<br /><br />Thanks for your help.

 

[BF]

Re: J25 dies in H2O

it depends on what year/model you've got... if it turns out that the spark is failing, and it's not just a bad spark plug, it could well be a bad coil. If it's an older one with points and the coils under the flywheel then I'd pop off the flywheel and have a look. If it's a newer one with CDI, and the coils out in the open, you could swap them around and see if the problem (spark loss) follows the coil.<br /><br />I'd also want to know the compression (first), so I'd know if I was spending (wasting) my time trying to tune up a motor that has a major mechanical problem, or is just plain worn out.... <br /><br />You didn't give too much background, have you had the motor for a while? When was the last time it ran good?

 

[fireman57]

Re: J25 dies in H2O

Sorry I've been gone for a while. When I say under a load I mean running in the water. Take insulated pliers and pull one spark plug at a time and listen for rpms to change. If they do not change then that cylinder is not firing. If they do then that one is fine. You did not give a model number so I don't know what year we are dealing with here but I would suspect a bad coil. If you find bad or no spark on once cylinder swap your coils and see if the problem follows thay coil. If it does just replace it.

 

[Marionboater]

Re: J25 dies in H2O

Thanks fireman57 and bf. Could not work on it the boat this weekend - too many storms. Will advise next week.<br /><br />FYI - the model is J25REND, a 1992 I think.