Johnson 115 Hp 1991 crossflow loss of power

I take it out, warm it up run up to WOT and back to Idle then WOT several times after only a few minutes loss of power then occurs . I have tested it on the water between each of the following repairs with no luck. Also runs fine evrytime at house.

Loss of power after warm up underload. I have replaced wires, plugs , carbs cleaned, rectifire,
powerpack, ignition coils, stator, checked compression 115-120 all 4. I'm just out of ideas. concearne about timer base and possible load up of fuel and exhaust. would appreciate any help.

Re: Johnson 115 Hp 1991 crossflow loss of power

hope it's not overheating and half-way seizing up.

Have you tried running off a remote tank to eliminate pick-up tube, anti-syphon, etc?

Re: Johnson 115 Hp 1991 crossflow loss of power

Sounds like the S.L.O.W. feature is engaging due to overheating...... knocks out the ignition on one bank, OR as above, the anti siphon valve (see below).

(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.

NOTE: There has been cases when the output valve in the fuel primer bulb would come apart, and the inner portion of the valve would actually reverse itself and be drawn back into the primer bulb's output valve body. This in effect would create a shut off valve and result in a fuel restriction. If this is the case, you should be able to feel something laying in the bottom of the primer bulb when held horizontally.

Re: Johnson 115 Hp 1991 crossflow loss of power

I can run the boat at Wot for miles with no problems it only occurs after several wot to idle wot sessions. So it feels to me like possible ignition or air flow carbon dioxide back up . the fuel tank is a separate tank than boat and it's pumps a solid strong steady stream of water even at low idle . Plenty of smoke from exhaust so good oil in mix

Re: Johnson 115 Hp 1991 crossflow loss of power

No knocks only rougher idle and smooth weaker power .

Re: Johnson 115 Hp 1991 crossflow loss of power

Weak ignition components tend to fail once the engine heats up to normal operating temps. Will run fine when cold, then worse as the engine warms up. Take an inductive timing light with you the next time you go boating. When the engine runs poorly, remove the cowling and check each of the 4 spark plug leads for spark. The flashes from the gun will show you misfires, intermittents, no fires, etc.
If everything checks out ok with ignition, then you can look at fuel issues. Best to check the spark when the engine is under load, such as idling in gear at the dock.

Re: Johnson 115 Hp 1991 crossflow loss of power

liljohn2424 said:

I can run the boat at Wot for miles with no problems it only occurs after several wot to idle wot sessions.

Click to expand...

Inspect, take a good close look at the stator under the flywheel which is the beginning of both the charging and ignition system. Should that stator be cracked and/or be dripping a sticky looking substance down on the powerhead area, that would indicate that the ignition side of the stator is failing. The clue is that the engine will have strong ignition (spark) when cool, but as it heats up, the igniiton/spark becomes weak and erratic... and eventually non existent.

Re: Johnson 115 Hp 1991 crossflow loss of power

after several water tests the #2 cylinder is loading up or possible weak spark (unsure_). I have tested by removing spark plug wires after the problem starts. pulling one plug at a time ( looking at the back of the motor the top left cylinder plug wire was removed while running poorly and had no effect on the idle or poor running condtion. the plug wire itself was sparking constantly while it was off and not transfering spark to the spark plug . all of the other plug wires pulled off one at a time caused the engine to shut off. So it seems to me that something is loading up or weakening performance after warming up or under heavy load. WOT to idle to WOT sessions. I have also tested by removing the heat sensor wire with no change.

Re: Johnson 115 Hp 1991 crossflow loss of power

The cyl drop test is a good/simple one to determine which cyls are not contributing to making hp. You've got 3 expensive potential culprits to check: Stator, Power Pack and timer base.

Re: Johnson 115 Hp 1991 crossflow loss of power

I have replace the stator with a used on the powerpack is new. Is there a way to know if it is the timerbase , or a way to test it considering it is sparking at the wire during the drop test? Does the timer base allow the powerpack to supply power to the coil and the plug at the correct timing with fuel to create fire and combustion? and if so could the timerbase be telling the #2 cylinder the incorrect time to fire {but still firing} and causing the cylinder load up?

Re: Johnson 115 Hp 1991 crossflow loss of power

When cranking the engine, the timer base should output at least 0.3 volts as measured with a special "peak reading" voltmeter. If not, it is a candidate for replacement. I believe there also may be some ohm tests you can do. Check out the troubleshooting at this website: cdielectronics.com

Re: Johnson 115 Hp 1991 crossflow loss of power

Today i took the boat out after replacing the timer base and the flywheel key. No change problem continues. So after it started acting up I stop the boat and changed the number two spark plug with a new one and the boat ran fine until same problem happen on the new plug. So i changed it it again and same thing ran fine. so I feel as if I have either a weak spark causeing load up or bad float or jets in carbs. Does anyone have any imput on the high spped jet and idle orfice or jet? Like how to tell of they are bad or any additional tests of what to do check any of these items. I also mentioned weak spark the only part I have not changed is the stator with a brand new one so i would like to know of a test to check stator for possible weak output. I have tried to read with a meter and nothing appears to be wrong, but I'm unsure of everything to look for. Thanks for your help

Re: Johnson 115 Hp 1991 crossflow loss of power

A high speed jet issue won't just "come and go," as you have indicated occurs with your engine. The jets either work fine at WOT, or it won't plane out at all, perhaps due to some blockage. Drastic intermittent problems are more typical of ignition issues. Ignition problems will come/go. If you check your stator, it should put out a minimum of 150 volts when the engine is cranked over-as measured with a peak-reading voltmeter. (You might want to warm the engine up first before you test it.)

Re: Johnson 115 Hp 1991 crossflow loss of power

similar problem rather in reverse order; since i bought this 100hp johnson 4 cyl. on a 89 Javelin the boat never got out of the hole but for a few brief moments and gave me 4,500 rpm or so. Starts, idles fine, full throttle does not get it over 3,000 rpm's mostly 2400-2500. After slugging around for a while if i power it down the idle goes rough and it stalls. To start again on a warm engine it takes to advance throttle in neutral position and then catch it in the right moment to put it in gear without stalling. Tried to clean up system with seafoam, put additives into tank which does not look like has any sediments. changed in line filter etc. Revvs up like mad on rabbit years but not under load in the water. Looked up manifold flaps; all 4 appear in order within specs as in the manual.

after changing spark plugs and troubleshooting ignition coils it appeared that it all work fine. Compression is similar in all cylinders 92-98 range.

Fuel looks clean, antisyphon valve taken out and put back in without apparent problem. Carbs took out and cleaned all orifices. Put new VRO/fuel pump combo. Swapped carbs (top to bottom) and it looked like left side spark plugs were consistently fouled following one specific carb (between cylinders 1 and 3). Ordered carb kits; thinking needle/float/gaskets issue but didn't have a chance to install it yet. If the carb kits wont do; will go to power pack/timing base/stator/flywheel diagnosis.