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Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 14384
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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Johnson 48 HP I have a 1995 Johnson 48 HP outboard motor.

Customer Question

I have a 1995 Johnson 48 HP outboard motor. The motor was placed in storage for a couple of years. When I tried to start using it again it would rough idle and sounded like it was only hitting on one cylinder. This occured from base idle through about 1/4 throttle. It would then pick up and run good on top end. I decided to pull the carbs and clean them. When the carbs were disassembled they appeared perfectly clean. Went ahead and cleaned them and blew air and carb cleaner through every passage. This did not improve the running issue. Took it to a local shop. He wanted to pull the carbs and clean them again. Which I paid him to do. Picked it up & went to the river to check it. Ran just as bad or worse as before. Brought it back to him. He worked on it some more replaced the plugs. Picked it up again. Ran it in the river. Appears to be running very rich and still running bad. Was able to improve the idle by leaning out the idle mixture screws. Now it will not run on top end either. Tried returning the screws to the original position. Still does not run on top end. Bogs down shortly after acceleration. Will not plane boat. Replaced the fuel pump thinking that the diaphram was busted. Adjusted the fuel air mixture once again. Idles fair but no top end. Totally frustrated!!!! Any Suggestions? I feel like the mechanic did something to kill the top end. Not sure. I have found he is difficult to get in touch with. Terry Morton
Submitted: 5 years ago.
Category: Boat
Expert:  Jason replied 5 years ago.

My name is XXXXX XXXXX I will be helping you today. Most questions will involve troubleshooting, and usually take many posts back and forth.

If you find it running rich, along with little power and rough running, and the carbs have been done twice over and a new fuel pump. The very first thing that comes to mind is low engine compression. And that is where you need to start, with a compression test. For your results, your looking for 90psi or better on each cylinder. If you come in much below that, then the engine has mechanical problems or is worn out. (or has rusted from the inside out from not being properly layed up for long term storage, but that would fall under mechanical problems)

Start with that and post back with any follow up questions or if it still gives you troubles.

Good luck!

Jason

Customer: replied 5 years ago.

Sorry..forgot to include that in the first post. 125 psi on both. Even though this engine is getting fairly old it doesn't have that many hours on it. I bought it used several years ago. When I installed it on my boat it ran like a brand new one. The only reason I put it in storage was due to a leaking tilt cylinder and I did not have time to repair it. Eventually I got enough time to replace the seal and now it runs like crap. FYI this motor is on a 16' flat bottom aluminum. I also went ahead and bought a new fuel line and used a different tank just to eliminate any problem that might exist on that end.

 

Thanks,

Terry

Expert:  Jason replied 5 years ago.

Terry,

2 more things to check here.

 

1. Double check your compression with a different gauge. Honestly 125psi is higher than I would expect for this motor when new. Compression gauges are known to go bad, and it wouldn't hurt to double check with a different brand tool just to confirm yours is accurate. I was expecting you to come in a 100 to 110 if the motor was good. Just from experience, 125 sounds a bit on the high side, and worth double checking.

 

2. Check your spark. You will need an adjustable spark gap tool for this. These are the testers we use in the industry.

http://www.stevensinstrument.com/spark_checkers.htm

 

But you can also get cheap spark checkers at most good autoparts stores.

You need to hook the spark tool up and set the gap to 7/16ths of an inch. The spark should easily jump that gap, be hot and blue in color, and be consistant with engine rpms. Weak looking yellow spark will not cut it. Look and see if your spark is weak or not.

 

Let me know what you get.

 

Customer: replied 5 years ago.
Double checked compression with another gauge. Still 125. Bought a spark tester. Bottom cylinder is firing consistantly. The top seems to have an intermittent fire. It will hit consistantly for a while and then start blanking out but not for long periods. Later tonight I'm going to check it again to make sure it is blue but it appears to be on both.
Expert:  Jason replied 5 years ago.
Intermittent spark is a common occurrence. Which is why when I asked you to do a spark test, I specifically wrote " and be consistent with engine rpms". But check it when you can see better and let me know what you get.
Customer: replied 5 years ago.

OK....sorry about the delay, had to work out of town for the weekend. Checked the spark again in the dark. Do not see any intermittent spark. The spark is blue and easily jumps the gap. Is it possible that one or both of the crank seals or leaking and causing a loss of crank case pressure/vacuum to the point of causing a running problem. Years ago my Dad worked on outboards for a side job and I remember him saying that this can occur. I have never heard of anyone saying they have had this problem but I agree with him that it could happen. I'm still leaning toward a carb problem. Sorry...didn't intend stray your diagnostic process.

 

Thanks,

Terry

Expert:  Jason replied 5 years ago.
Its possible its crank seals, but that is the last resort only after you have checked everything else, already rebuild the carbs ect, as there really is no way to check the crank seals while the engine is running.
Customer: replied 5 years ago.
What would you try next?
Expert:  Jason replied 5 years ago.
Did you check spark when the engine was stone cold? Or was it running awhile?
Customer: replied 5 years ago.
It was cold with both spark plugs disconnected so it would not try to start.
Expert:  Jason replied 5 years ago.

I would run the engine and let it warm up, get good and hot. And then check spark again. Heat affects ignition components, and can cause them to fail.

 

Another way to do it as well is to hook up a timing light as the engine is running and hit the strobe button. If the light flashes consistantly with engine rpms, spark is good and consistant. If the light is erratic, then spark is erratic.

Jason and other Boat Specialists are ready to help you
Customer: replied 5 years ago.

Well...I have finally admitted that I do not have the time to keep playing with it. Taking it to another shop this evening. Maybe I'll get better service than the last one...hopefully. I'll let you know what they find. Thanks for all of your help!

 

Terry

Expert:  Jason replied 5 years ago.

Your very welcome.

If you don't mind, after you get her up and running, come on back and let me know what the issue ended up being.

Good luck!

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