Stumped

[Mojo^]

I have a 1997 Johnson 25 hp. model no. J25REUM. It starts just fine, idles okay and will accelerate. When I begin to increase the throttle and at higher rpms it begins to sputter and misfire. I have a new gas tank with fresh gas and oil and the fuel filter is clean. When I let off the throttle quickly there is a lot of popping. There seems to be a lot of oil in the exhaust and it will continue to drain from the exhaust for quite some time after the engine is shut off, but not always. Both spark plugs are new and the gaps set to .030. After running the engine, both plugs are wet and have oil residue. I've tried to adjust the carburetor mixture but seem to get very little difference in engine operation at any setting. There is a lot of smoke in the exhaust but it's not consistent. At times it's light and at other times very heavy. Last weekend I did a spark test and was getting an intermittent spark on the #2 cylinder so I changed the coil with no difference in engine operation. It seems like it may be misfiring in one or both cylinders. I'm lost and don't know where to turn next. Is it the carburetor? Is it the power pack? Or, is it something more serious?

 

[Lyle29464]

Re: Stumped

My guess is your spark tester needs to be grounded better and the gap checked. I think your high speed jets are plugged.

 

[Daviet]

Re: Stumped

You have only a low speed adjustment, the high speed is fixed.
You siad you changed coils, did that correct the loss of spark on that cylinder?
Where is the popping coming from, carb or exhaust?

 

[DJ]

Re: Stumped

They will "pop" on RAPID decel.

You need to get a strong consistant blue spark on both. At least a 1/4". Check your checker.

 

[Mojo^]

Re: Stumped

The popping seems to come from the exhaust on rapid deceleration. It sputters during acceleration and at higher rpm.

 

[Mojo^]

Re: Stumped

You need to get a strong consistent blue spark on both. At least a 1/4". Check your checker.

To be honest, I'm not even sure I'm doing it right. I'm using a regular automotive spark checker and putting it between the spark plug and the spark plug wire boot. One end attached to the spark plug and the other to the wire. Since the maintenance manual stated that this should be done with the engine running, I knew of no other way.

 

[Lyle29464]

Re: Stumped

sounds like your spark is fine. It's jumping 2 gaps. still think it's the carbs

 

[Mojo^]

Re: Stumped

I've been running it with just muffs but this morning I put it in a tank. As soon as I had water providing some back pressure to the exhaust I could tell right away that it is occasionally misfiring at all rpm's including idle. I think I'll order a kit and do a thorough cleaning.

When I first began working on the motor last week I noticed that the wire going from the power pack to the #2 coil had a small spot where the insulation had melted and bare wire was touch the upper mount bolt on the #2 coil. I wrapped it with electrical tape and replaced the coil with no difference. I don't know how long the wire had been grounded against that bolt but can't help but wonder if that could have caused the power pack to go bad.