1988 Johnson Outboards 15 [ J15RCCS ]

[RTripp]

15 hp Johnson has been causing me a lot of work. I have rebuilt the carb twice and replaced the fuel pump. But, I still have the same problem. It will start, idle all day and run nicely between 5-10 mph. When I open it up it will run for about a mile(23 mph) and then bap bap ba bap bap bap and lose power. I let it run in the 5-10 mph for awhile and then open it up again and it runs good for 1/2 - 1 mile and back to the baps. But, It never dies.

 

[racerone]

Test run with another tank and hose.

 

[RTripp]

Yes, this was a test run with a new tank. Not a new hose though.But, the hose is OEM and about a year old.

 

[RTripp]

I have an old 9.5 I will try this weekend and see if the hose might be an issue.

 

[Joe Reeves]

At full throttle, have someone pump the fuel primer bulb constantly acting as a manual fuel pump. If that cures the problem, you either have a fuel/air leak somewhere OR a failing fuel pump.Yes I know that you replaced the fuel pump but that doesn't guarantee that it functions properly.

 

[fireman57]

Make sure the cap is vented or loosen it.

 

[RTripp]

Thanks for the responses. I am able to reach the primer and I tried pumping as the Ba Baps were happening. The bulb was almost full and pumping did not help. The tank is an Attwood, 6 gallon, the paper that came with it said do not loosen cap. The new cap is supposedly vented. Well.... with the cap tight and tank sitting in the sun it swelled up a lot. They state this is normal. Well...... I loosened the cap anyway for better venting.

So...nobody thinks this is an electrical issue or overheating issue? I'm not a mechanic and I don't pretend to be. But, I can do some work with the help of some Youtube videos.

 

[RTripp]

I put my 1969 9.5 johnson on 14' jon boat and went to a lake today. When I got away from the dock I opened it up and it was acting like the 15 hp, sort of. . So, I thought GOOD!! I'll just buy another hose. But, then I got to thinking......I'm 200 lbs. this 12 volt battery is 80-90 lbs. This electric motor is more weight and the anchor is more weight. This old motor can't get up on plane because of all this weight. So, I moved the battery, cooler, anchor, tackle box up to towards the front of the boat and the old motor was able to get up and go. We got up to 14.5 mph and she ran about 5 miles with no bap-ba-bap- baps like the 15 hp was doing.

The 15 hp can push me and all that weight in the back about 23 mph. But, she has issues.

Any more ideas?

Thank you

 

[thatone123]

Get an old OMC 20 built before 1976...Weights only 5 more pounds than the 9.9/15 and will haul a ton of weight on plane.

 

[RTripp]

OMC--interesting. I don't know of this motor.. Thanks for the suggestion.

 

[RTripp]

I did some investigating this afternoon. I put the 15 in a garbage can and cranked it up. I pulled top spark plug and the motor died right away. I then plug that one back in and unplugged the lower one. The motor ran for about 5 seconds and then died. I pulled the plugs and they look pretty good. Almost clean. Very little coloration. I hooked up a spark plug tester and it lit up. I then did a compression check. It was 120 in each.

I am in the process of rebuilding the pull starter coil, spring, so I used a drill to spin the flywheel. I only spun it around about 5 times.
The spark plug wires are Sierra brand and only a year old. The plugs are Champion L77JC4. gapped .030 There wasn't any water or little droplets on the plugs.

 

[fireman57]

Sounds like weak spark. Check it with an open gap spark tester and make sure it jumps about 7/16" with a blue spark. Orange spark is not enough. Might be as simple as a bad coil. You can also physically swap the coils and see if the problem follows. If it does just change the offending coil.

 

[RTripp]

Thanks for the responses

I just pulled spark plugs and put them about 1/2 inch from block. The top one first- it shot a nice spark and got the motor running. Bottom one- not much of a spark and it didn't get the motor running. I have to order new plugs. Amazon Prime. They will be here Thursday.

So, while waiting for new plugs I will attempt to fix pull starter.

Spark plug tester ---I went to two auto parts stores and all they had was the inline light up. I'll check Amazon for the one you suggested.

After installing new plugs I will check coils

Thanks

 

[oldboat1]

Seems to act up when hot and under load. Think I would replace the power pack.

 

[RTripp]

I got an ignition tester today and I tested the coil/spark plug wire at 5/16", 6/16, 7/16 and there was good spark. When I went to 8/16" I saw sparks shooting out the back of the boot on the lower line. I'm getting two new spark plug wires and two new spark plugs even though the plugs looked good.

Hopefully this will be my only problem. I will find out either Friday morning or Saturday when I can take it to a lake.

Thank you everyone. I'll let you know how it goes.

 

[fireman57]

The bap bap bap could have been the spark arcing to ground from the bad boot. Hope it works.

 

[RTripp]

Thanks to all who helped me with this issue. Joe Reeves made a suggestion that it could be the slow speed needle on 9.9 and 15 hp johnson and evinrude could cause a cylinder drop if the needle is not adjusted correctly. I had the needle adjusted at 1.5 turns sometimes I even tried up to2 turns and the cylinder would drop. However; with Joe's suggestion I made a 1 revolution turn and it worked. Both cylinders now operate at peak peak performance. Amazing!! Many thanks to Joe.I did a test on a lake. I went for about 10 miles at WOT or close to it and she ran perfect.

 

[Joe Reeves]

A whole turn on that slow speed needle valve, to me, seems excessive... BUT... if it idles normally as well as the top end, I would think... leave well enough alone.

However the mechanic in me would have me (personally) tearing into that carburetor as with that needle valve turned a full 2-1/2 turns out, the engine should load up with fuel to a point whereas it floods out and stops running. But then again, to re-use the phrase once more... "However", since it works for you, and if it continues to work for you, leave it be until the next problem pops up. Keep us up to date.