1986 140hp Johnson - Skipping at full throttle but not after engine warms up

[Robbiecd]

This is a problem that has gradually gotten worse over the last two seasons. I get on the water and start the engine, maneuver out past the no wake buoys at about 1/4 throttle. When I slowly throttle up to about 3/4 throttle and approach plane, the engine suddenly starts skipping violently and slows down until I bring the throttle back down to about 1/2. Then it runs fine at this low speed. After it warms up, usually an hour or two later, I will try several times to get it up on plane and eventually it will do fine, running at wide open throttle for miles. Then the problem disappears for the rest of the day.

I am hoping that this makes sense to someone. I want to fix it before spring. Any advice would be very much appreciated. Thanks in advance.

[Robbiecd]

I could really use some help with this.

[Randy J]

hmm been a long time since ive had outboards did you make sure the gas tank vents open?

[HighTrim]

Does it sound like a backfire?

[Robbiecd]

Yes, the vent is open, you can hear it blowing air when you press on the plastic fuel tank.

By the way, I have a series of about 70 photos of the engine that I took during disassembly if anyone needs to see a part of the assembly.

I recently rebuilt the engine to investigate for problems, since I got it used and had no idea what its history was. It looked like it had very few hours on it, and I could find no obvious signs of neglect or damage, so I replaced the gaskets and seals and put it back together. I don't want this rebuild to clutter the post, however, since the problem with skipping at full throttle was present before AND after the rebuild. There seems to be no change in performance.

[Robbiecd]

No, it sounds like it's stumbling or stuttering, and you can hear the rpm dropping. Sometimes it sounds like it 're-engages' and it lurches forward.

[wilde1j]

You mean you tore the engine down without a clue of what was wrong? You should try some logical trouble shooting as a first step.

How long has the motor exhibited the violent missing? What has happened since then? Are you sure the timer base isn't sticking? Such violent shaking is usually consistent with a timing issue, but there may be other causes as well.

[HighTrim]

Unfortunately it will be hard to diagnose and cure in the winter without testing. You dont want to just throw parts at it.

I would start with the basics here to diagnose. Ill assume you checked compression during all the rebuilding? What were your numbers?

When it is acting up, bring an inductive timing light and test to ensure that she is firing on all cylinders.

The violent nature leads me to believe that you are not simply dropping a cylinder, but cant hurt to start with the basics.

Is this a built in tank or portable?

[Robbiecd]

Actually, I haven't checked compression yet. I'll have to buy the tool and test it, especially if you think that could aid in diagnosis. The tank is a big rectangular plastic box that could be removed if needed, but it isn't your typical portable tank.

[Robbiecd]

The missing has gotten worse each season, but I've only had the boat for four years. Would a timing issue correct itself after the engine warms up?

[wilde1j]

The missing has gotten worse each season, but I've only had the boat for four years. Would a timing issue correct itself after the engine warms up?

If grease has been used on the timer base, yes it could stick, until the motor heat thins it. I would assume you used an OEM shop manual as part of the teardown and followed all instructions regarding use of lubes, etc.

Another area to consider, and this would be bizarre, is an ignition component is reacting favorably to being heated. Usually the reverse is true. If possible, try heating diffent component areas (i.e. powerpack(s), coils, stator, etc.) with a heat gun (don't get too carried away with the heat) and observe the results.

As suggested above, I would check the timing and also very the timing pointer is in the correct place.

[Robbiecd]

I used the manuals for the teardown and reassembly, and applied lubricant where instructed. The timer base seems to be moving smoothly, but rod in the link assembly that connects to the timer base seems a little sticky, it looks like it is full of grease. Could that be causing my problem? How do I go about fixing it?

Is it worth buying a test wheel (to replace prop while in test tank)? Is there any other way to run the boat at full throttle out of the water? I can't imagine that performing the appropriate tests while on the water is safe.

Thanks.

[Robbiecd]

Does anyone have some suggestions regarding the last post?

Thanks,
Robbie

[Robbiecd]

BUMP. Please see my questions in post #12.

[SparkieBoat]

Have you done the compression test yet?? First thing to do anytime you are having skipping issues is check spark and compression, and change/install a water fuel separator and any fuel filters under the cowl. This will require a spark gap tester and engine compression gauge, both are readily available for low cost at most auto parts stores. You got way ahead of your self by tearing the motor apart, now you may have caused a air leak somewhere. after spark and compression are checked, you need to do a good carb cleaning/rebuild, detailed instructions in the secret files section at top of forum. then buy yourself a timing light and check the timing, also detailed instructions in the secret files. doing test on water is safe as long as you have a friend to help..but if you want to invest in a test wheel system go for it, they are nice to have, wish I had one. I river test all my motors. also make sure you are not getting any water in your fuel tank, small amounts of water intrusion will cause intermittent high RPM skips, or just bad fuel.

[Robbiecd]

The carbs are crystal clean, which suprised me. I agree about tearing the motor down, but I was extremely careful to follow ALL proper procedures. I just wish that I had invested in the tools to check the compression and timing as a final step. I can see all of the vetrans out there reading this thread and shaking their heads. Bear with me.

I'll try the tests listed above and let you know what I find out. I would especially like to take a close look at the engine while it is skipping, to see if the timer base seems to be sticking.

[SparkieBoat]

I do not think that your timer base is sticking, but if it is then a timing check will reveal if there is a problem. do the things listed above first..this is a step by step process, dont get ahead of yourself.
O yea I hope you have replaced the plugs with the correct Champion plug and gapped them all properly.
this is actually the first thing to do in a skipping/missing situation.