1988 Johnson 40 has me stumped...can't diagnose

[sideeffect]

I have a 1988 Johnson 40HP (VRO removed) that has run perfectly until this spring. One day in March, after running fine for a half hour, I got an overheat alarm, and it apparently went into SLOW or LIMP mode. I immediately killed the engine, put on trailer and swapped out the thermostat and water pump. Ran great after that afterwards for a couple of weeks with no alarms....then all of a sudden it would start bucking when throttled up (similar to what it did during the previous overheating incident)...but no alarms. Still ran perfectly at low RPMs and at idle.
After researching, I cleaned both carbs ensuring all jets were clean, changed the coils, spark plugs, and spark plug wires. I've disconnected the brown wire going to the temp sensor, still no change, so I reconnected it. Still can't get it to run right at high RPMs and the best I can describe it is that it acts like it's a bucking bronco. I cannot get a local mechanic to even look at it due to it being a two stroke. I'm fairly good with a wrench and could possibly fix myself, but obviously need some help diagnosing. My boys and I restored the entire boat last year and they are chomping at the bit to get it back out on the water.

 

[racerone]

That is not a 1988 model !--------I say 1990 model.------Could be an issue with gears in the lower unit.----These lower units are NOT ROBUST at all.-----Drain gear oil and check magnet on drain plug.

 

[racerone]

Post model # here.------Was water pump kit installed or just an impeller.----Grommet from pump housing to water passage in place ?-----Shift rod height checked ?----Could be jumping in and out of gear.

 

[sideeffect]

Model #:TJ40ELCEC

Yessir...the entire water pump kit was replaced. I did everything according to the service manual so I'm hoping that the grommet is in the correct position. It's peeing great and engine isn't overheating.

It shifts in and out of gear fine, but I did have to disconnect the shift rod when I did the water pump. Perhaps its not at the correct height and causing some sort of shift dampening effect....not sure how to check the shift rod height.

The motor does the same thing when in neutral....runs absolutely perfect at idle but starts bucking at around mid throttle (fast idle).

 

[racerone]

A 1989 model.-----Do a spark intensity check.-----Does spark jump a gap of 7/16" on a test device ,on both leads, yes or no ?----Post results of a compression test.----Post picture of the fuel pump that is now installed on it.

 

[sideeffect]

Thanks for your willingness to help.

I don't have a spark tester but can get one tomorrow and post the results. I do know that both are firing because I was shocked by each when testing them (using the dumb way obviously).

Compression at both cylinders is at 170'sh and I've attached photos of the fuel pump. I wish there was a way to attach a video of what it is doing but not sure there's away to do that.

 

[sideeffect]

I read a few things about a faulty "blocking diode" as the culprit but can't seem to find where that is located.

 

[racerone]

Where did you read about a " blocking diode " on your motor?-----Did it refer to your 89 model 40 HP in that reference ?

 

[faztbullet]

Could be a faulty UFI pack

 

[sideeffect]

Really appreciate everyone chiming in...hopefully, I be able to return the favor somehow.

I read a few threads about a blocking diode being the problem on a few OMC mid-80's/early 90's motors that were experiencing same symptoms, but nothing specifically pertaining to 89 models.

I just bought a wheel puller and am going to pull flywheel off this afternoon. Will report back with findings.

 

[sideeffect]

I am researching the parts diagram to get my bearings before I start disassembling everything. In the attached diagram, which component(s) make up the UFI ignition system? I figured it could be the thing circled in red or yellow...or both. The parts list isn't very descriptive.

 

[sideeffect]

I just got the flywheel off and nothing seems broken. However, I did notice there was a sticky black substance that seems to have leaked out of the bottom of the charge coil (maybe melted plastic??). Could this have been fried during the overheat? Could a faulty charge coil cause these symptoms? Photos attached.

 

[racerone]

Yellow is the CDI unit.-----Red is the battery charging unit.

 

[sideeffect]

Thanks Racerone....is the CDI unit the same as the UFI pack?

Also, I just attached pictures of the underside of the flywheel and charge coil. The charge coil looks to have some of its potting material melted and smells burnt. I would like to test the coil but can't find my darn service manual...I think my wife has hidden it.

 

[faztbullet]

That is the charge(stator) for the UFI unit

 

[faztbullet]

Just convert it using CDI-113-4489

 

[sideeffect]

Wanted to follow-up on this in case someone else happens to run across a similar situation. The problem ended up being the power pack...after replacing that, it ran perfectly.