1990 Johnson 120hp Cuts out @ 2500rpm

[Jon H]

Need some help: Replaced VRO with new fuel only pump and am using pre-mix. All new fuel lines from tank to carbs. Idles great at home on muffs. Took out on water, starts and runs fine up to 2500rpm, after that stumbles like you are turning key off and on, until you back off throtle, then idles fine again. Had same problem before removing VRO. Fuel tank was drained and fresh fuel (50:1)put in tank. I have a new water separator installed. sounds like electric problem? Coils? Ran fine last season. Any ideas?

 

[Joe Reeves]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

You say that if you try to exceed 2500 rpm, it "stumbles like you are turning key off and on, until you back off throttle."

That explanation would lead a mechanic into the ignition system... BUT... is that stumbling actually a very sharp cut out/cut in type happening (ignition)... OR... more of a gradual type loss and gain of rpms (fuel)?

If a sharp cut out/in type happening, look over the wires that would move which lead from the timer base to the powerpack etc... the wires themselves, the rubber connectors, the pins and sockets within those rubber plugs as they have been known to become pushed back slightly (bad connections).

If a gradual cut out/in type happening, the high speed jets (one to a carb) located in the bottom center portion of the float chamber (in back of that large brass screw) may be somewhat fouled. Clean them with a piece of single strand steel wire (carb cleaning solvent just doesn't do the job properly).

Do you receive any kind of warning sound from the warning horn? Does that horn beep once when you turn the key on?

With the spark plugs removed, the spark should jump a 7/16" gap with a strong blue lightning like flame... a real SNAP! Does it? Note that the 7/16" gap is important. You can use a medium size philips screwdriver inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark.

Does the fuel primer bulb have a tendency to be drawn flat when this problem occurrs (fuel restriction)?

What spark plugs (make and code numbers) and gap are you using?

 

[Jon H]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

NGK BPZ8HS10 (.030) Yes very sharp and fast cut in and out. Horn beeps when when key is turned. Removed VRO and wiring. New fuel only pump, (50:1 pre-mix). Have to do the spark test, Do the coils act different at higher rpm? (Hotter) Primer bulb does slightly flatten when cut out happens. Cleaned high speed jets with carb cleaner only, no wire. The plug connectors looked clean and secure (inside & out) from timer base to power pack.

 

[Joe Reeves]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

I prefer the recommended Champion spark plugs, you might try them for comparison. Also, although the present recommended gap is indeed .030, the original recommended gap from 1973 to somewhere in the 1990's was .040. Various engines seem to have either a better idle or better performance at full throttle with one gap setting of the other... varies from engine to engine, I have no idea why.

The only difference in the coils at the higher rpms, to my knowledge is that they are forced to fire faster.

The thought of having the full throttle spark advance timing set too high crossed my mind BUT backing off the throttle slightly only affects the throttle butterfly setting.... the timer base stays where it's at until the throttle is closed quite a bit.

The fuel primer bulb going flat indicates a fuel restriction somewhere between the primer bulb and the fuel supply. YOu might want to check the following.

(Fuel Anti Siphon Valve)
(J. Reeves)

Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vacuum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.

NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models.

The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction. Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.

The above procedure will cure a restriction problem with the anti siphon valve as stated. BUT, it may also allow fuel to drain backwards to the fuel tank when the engine is not running (siphoning backwards) due to the fact that the carburetors/fuel pump etc are higher than the fuel tank. This condition is not an absolute as the valves in the fuel primer bulb usually prevent this backwards siphoning problem. However.... if this does take place, the cure would be to install a new anti siphon valve.

 

[Jon H]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

Checked spark, jumps 7/16" gap but looks thin to me? What exactly does the spark dwell adjust do? How do you set it? Removed all 4 coils and cleaned brass ground tabs and engine block contact points. I have a video of the motor on the water running and acting up at 2500rpm. Can't figure how to download it to the post.

 

[Jon H]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

See boat underway in below link.

http://www.youtube.com/watch?v=b8J9Bslr8aM

 

[Joe Reeves]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

That looks like a definite ignition breakup to me.

Your statement of "Checked spark, jumps 7/16" gap but looks thin to me?" makes me wonder about the condition of the stator under the flywheel (a two fold component). One portion of it, two coils located usually at the rear of the stator are the beginning of the ignition system.... supplies approximately 300 AC volts to the powerpack.

Should the stator start to overheat to a point where either of those two coils start to melt down and start dripping a sticky looking substance down upon the powerhead area, a voltage drop takes place which results in weak, erratic, and eventually no ignition. Inspect those two coils and the stator in general closely. Should that stator be encountering a meltdown situation, replace it.

 

[boobie]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

As Joe said, you do have a definate ignition miss in it. Could also be the power pack as some will go into SLOW for no apparant reason. It might also be the blocking diode in the wiring harness.

 

[Jon H]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

I had the boat out this weekend and ran great at idle and at low rpm. Its been rough starting thou. turns over for a split second, sounds like it fires. then the starter morot kicks off. I have to "bump" the key about 6-12 times then it will start. Its not just cutting out at 2500rmp anymore. Seems to cut out when ever it wants. Some times even got up to 4000rpm before break up??? Need to do ohms tests on stator, timer base, etc.... Hate to start replacing things that don't need to be replaced. Thanks for all your ideas.

 

[Joe Reeves]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

Be sure to visually inspect that stator for a melt down condition.

 

[Jon H]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

Removed flywheel & stator. The stator is a sealed unit. The coils are not visible. The stator itself looks clean. However there is a brown wax-like substance in one spot that has dripped onto the powerhead. (see photos) I did switch plugs to the champions Joe suggested .040 gap. Is there a way to test the stator?

 

[Joe Reeves]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

Unfortunately I do not have the books on that model, but yes, there is a way to check the stators ohm resistance and also the output voltage. Hopefully some other member will jump in here with those specifications.

I cannot see where the stator is dripping anything down.... perhaps it is, I just can't see it. Notice the wider parts of the stator at the forward and rear portions of it. I know they're sealed units but those wider areas are where the two larger coils are located that provide AC voltage to the powerpack. If there's any leakage, it would be right directly under those areas.

When reinstalling the flywheel, be sure to torque the flywheel nut to 105 foot pounds. Anything less will result in a sheared flywheel key.

 

[Jon H]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

Forgot to mention, the tach seldom works, very intermittent. Fuel sender and gauge were replaced & are not working. Could this be a sign of a bad stator?

 

[Joe Reeves]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

Forgot to mention, the tach seldom works, very intermittent. Fuel sender and gauge were replaced & are not working. Could this be a sign of a bad stator?

I don't see how that would affect the Fuel sender or gauge, but the tachometer is another matter, as follows.

(Testing Tachometer With Water Cooled Regulator/Rectifier)
(J. Reeves)

A quick check is to simply plug in a another new tachometer as a piece of test equipment. If the new tach works properly and the old tach didn't, obviously the old tach is faulty.... but usually boaters don't carry around a spare tach (see below).

A faulty rectifier wouldn't damage the tachometer, the tachometer simply wouldn't work. This is due to the fact that the tachometer operates off of the charging system and the rectifier converts AC voltage to DC voltage, enabling the charging system. A faulty rectifier disables the charging system, and the tachometer simply doesn't register.

However.... those water cooled regulator/rectifiers that are used on the 35 ampere charging systems (and some others) bring into play a different type problem, and as you've probably found out, they are really a pain to troubleshoot via the proper procedure. There's an easier way.

The tachometer sending/receiving setup operates off of the gray wire at the tachometer. That same gray wire exists at the engine wiring harness which is connected to the engine electrical terminal strip. You'll see that there is a gray wire leading from the regulator/rectifier to that terminal strip, and that there is another gray wire attached to it. That other gray wire is the wire leading to the tachometer which is the one you're looking for.

NOTE: For the later models that DO NOT incorporate a wiring terminal strip, splicing into the "Yellow Wire" mentioned will be necessary.

Remove that gray wire that leads to the tachometer. Now, find the two (2) yellow wires leading from the stator to that terminal strip. Hopefully one of them is either yellow/gray or is connected to a yellow/gray wire at the terminal strip. If so, connect the gray wire you removed previously to that yellow/gray terminal. Start the engine and check the tachometers operation, and if the tachometer operates as it should, then the regulator/rectifier is faulty and will require replacing. If the tachometer is still faulty, replace the tachometer.

If neither of the yellow wires from the stator is yellow/gray, and neither is attached to a yellow/gray wire, then attach that gray tachometer wire to either yellow stator wire, then the other yellow wire, checking the tachometer operation on both connections.

I've found this method to be a quick and efficient way of finding out which component is faulty.... the tachometer or the regulator/rectifier. It sounds drawn out but really only takes a very short time to run through. If the water cooled regulator/rectifier proves to be faulty, don't put off replacing it as they have been known to catch on fire with disastrous consequences.

 

[Jon H]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

I preformed the above test method. Connecting the gray tach wire to the yellow/gray terminal strip DID make the tach work. Just wondering if the regulator/rectifier is my whole problem with the cutting out?

Also while I had the flywheel off I cleaned the inside of the flywheel aswell as the outside of the stator with a scotchbrite. Some light surface rust existed.

 

[Joe Reeves]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

I preformed the above test method. Connecting the gray tach wire to the yellow/gray terminal strip DID make the tach work. Just wondering if the regulator/rectifier is my whole problem with the cutting out?

It's always possible that two problems may exist, however.... the tachometer test has proven that the regulator/rectifier assembly is faulty and needs to be replaced first before it causes the engine to catch fire.

 

[Jon H]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

Replaced the regulator/rectifier, tachometer works 100%, thanks Joe. Replaced spark plug wires w/ new oem ones. Still cutting out when giving throtle above 2000-2500 rpm. Still starts hard, with starter only ingaged for a second then slips off the flywheel. Still scratching head? Only a few more parts to replace....
Only things left to replace are stator, power pack, timer base and coils.

 

[Jon H]

Re: 1990 Johnson 120hp Cuts out @ 2500rpm

Problem solved. Was one of 3 things. either stator, timer base or power pack. Found a guy on ebay selling a complete electrical system/harness from a '91 140hp. All #'s matched. Got it for $90. So I replaced the major 3 problem children. Success. Thanks for everyones help!