1992 Johnson 115 - 2250 rpm's at WOT

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Ginder75

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I have a new to me 1992 Johnson 115, Long shaft, Pwr T&T, ... (sorry, I left the Model number at home).

The motor is installed on a 17 foot BassCat with a 21 pitch prop. I have replaced the plugs, cleaned the carbs, and run several gallons of gas with seafoam through the motor sitting in the driveway.

The problem - The motor has no power, at full throttle the motor is turning 2250 rpms and the boat is traveling at 7 mph.

The tank is vented, the fuel bulb remains firm, and I have resonible compression 115-110 on three cylinders. The forth is at 85 psi, but the more I run it the higher it gets. I am planning on rebuilding the power head later, but I want to feel the wind in my hair before I pull the power head off. The olds plugs were REALLY nasty, I thought a good Decarb might help the compression, but with no WOT it is hard to do.

Thanks for all the help,

I must be a glutton for punishment. I get one motor running and I sell it for a bigger bag of problems.
 
R

R.Johnson

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Re: 1992 Johnson 115 - 2250 rpm's at WOT

I think you found your problem. Pull the head, and take a look at that cylinder
 
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emdsapmgr

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Re: 1992 Johnson 115 - 2250 rpm's at WOT

Any chance the engine is overheating? That unit should have the "slow" system on it. If the engine overheats, the power pack will limit the engine rpm's to 2500. Sort of a coincidence.
 
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Ginder75

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Re: 1992 Johnson 115 - 2250 rpm's at WOT

I was wondering about the "Slow" system, but I could not find any reference to it in my manual. The motor acts up from the first start of the morning throughout the day.

If I disconnect the two therma-coupler leads will that by-pass the system? I will not run it excessively, but I want to hit WOT before pulling the motor, swaping thermostats, rebuilding the powerhead, or anything along those lines.

I have a laser thermal device (point and take the temperture), can I use that on the block to see what the current operating tempature is at WOT?

What range am I looking for?
 
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emdsapmgr

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Re: 1992 Johnson 115 - 2250 rpm's at WOT

The engine should idle around 145-150. The thermostats open at 143. The hot alarm will go off at 212 and silence again at 175. It will run cooler once you get up to speed, and the pressure relief valves open. Even if the engine is not overheating, if the power pack receives the signal that the engine is hot, it should limit rpm's. The heads or top of the cylinders are good places to test for temps. I would also shine a light into the spark plug hole on the 85 lb cylinder and see what the top of the piston and liner walls look like.
 
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Ginder75

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Re: 1992 Johnson 115 - 2250 rpm's at WOT

I did not have a chance to take the boat out last night, but I did test the warning horn. It sounded when I grounded out each temp. sensor. So, I guess a bad sensor is not my problem. I was hoping for a cheap and easy solution.

I am going to try a few other checks, but I am at a loss on this one.

The motor starts without issue at home (two or three turns of the key for the first time, and within a 1/32 of a rotation any time after that). Once the motor is running, as soon at the starter hits the flywheel the motor comes to life! I know the low compression is a problem, and needs to be addressed. But I can't see one cylinder causing this much reduction in performance.

I have GREAT spark at idle, The spark will jump 1/2 - 1 inch of open air and seems to hit every time around. Could I have a bad/limited CDI? This thing will idle all day long on the hose, but it seems to lack power on the water.

Thanks for the help,
 
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emdsapmgr

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Re: 1992 Johnson 115 - 2250 rpm's at WOT

Just checked the service manual, and in 1992, of the crossflow engines, only the V6 engines with 35 amp alternators had the slow system. Sorry for the confusion.
 
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Ginder75

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Re: 1992 Johnson 115 - 2250 rpm's at WOT

Well, that would explain why there was no reference to it in my model specific service manual.

Would a bad CDI allow it to run normally at idle, but drop out at WOT? I am not looking to blindly replace parts, but at idle this thing seems great, but when it is time to GO, there is NO GO!

I had a similar problem on a previous motor and turned out I was flooding the lower cylinder, and adjustment of the carb and I was good to go. But there are no adjustments on this model.

Thank for help, and if you think of anything else that would limit my RPM's to 2250 at WOT pass me a line.

I am not going to let this motor beat me down!
 
tashasdaddy

tashasdaddy

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Re: 1992 Johnson 115 - 2250 rpm's at WOT

just a thought, there's section in the manual, about link N sinc, could be out not letting the timing go higher. it's just a wild hair thought. have you checked to see if the shifter throttle cable i pulling the linkage to wot.
 
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Ginder75

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Re: 1992 Johnson 115 - 2250 rpm's at WOT

The valves are perfectly pararell to the bottom of the carb, and the timing is advancing (just a little), I will get a guage on it too see. But the movement of the timing assembly is miniscule. All parts seem to move freely, and return to normal starting positions when shifted in neutral.

I had a buddy set on the rear deck and manually pull the carb linkage and the timing linkage to see if there was any more movement. 2250 is all the motor will turn.

Thanks for the thought, but I thought the same thing when I heard it run. I just knew the linkage was out of whack, but so far, I can't track down a problem.

Anyone else got an idea?
 
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emdsapmgr

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Re: 1992 Johnson 115 - 2250 rpm's at WOT

Sound like you are slowly working through the items on your checklist. Running the engine on a hose does not tax the engine ignition system the same as when it is under full load. Take your buddy to the lake with you. Test the boat in the water: Connect a timing light to each plug wire. Run at WOT. See if you are getting strong, constant, rythmic flashes from the timing light. That will tell you if you are getting good fire, or an intermittent miss, or only spark on 3 cyls, etc. Electrical components tend to break down when they are hot, or under heavy load.
 
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Ginder75

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Re: 1992 Johnson 115 - 2250 rpm's at WOT

Okay,
I had the Ohm meter out, the instructions on the rear deck, and a cold coke to help me along the way with this. But I have a question - What the heck is DVA?

All the instructions say Check the DVA on the stator, timer base, .... They provide the wire colors and what range the Ohm reading should be in, but there is no definition of DVA.

Sorry for the bone-head question, but before I start sticking my probes in places that they should not be I thought I would ask.

Also, are these tests done with the key in the on or off position? Battery connected?

Anything else I need to know?

Thanks,
 
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