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1998 50HP SLOW Mode Issue

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Dqracine

New member
I have a 50HP engine that is going into SLOW mode after running at high speed for a sort period of time. I get no warnings from the engine controls. Motor will run fine if I remove the engine cowl. I have had the water impeller replaced, and I have checked engine compression and get readings of 125-130PSI on the two cylinders. What else could be causing this condition? I have been told engine coil or power pack but not sure if there is a way to determine which it may be.
 
It could be a bad temp sensor. Disconnect it and run it. If it doesn't go into SLOW you'll that was it. If it still does, could be a bad pack.
 
I have a 98 50hp 3 Cylinder that won't go over 3000 rpm under a load but goes to 6000 rpm when proped up could this be the same problem . I have pumped the balb and choked it with no change except for dieing when choking so it is not the fuel pump or a pluged carb.
 
I bought a boat with a 2000 mdl 60hp johnson, when i bought it the fella told me that theyve just changed the plugs and filters but havent been out in the boat since.
Turns out it runs religiously for approx 10 mins then going into slow mode, shut it down for 5 mins and away she went for another 10 mins running fine and then same again, no alarms and warnings at all triggered, major problem while off shore, checked running temp on the water with ir gun and running at around 140f, tried to test temp sensor in heating water still came up with no continuity at boiling, would have said that was buggered but i put it back in for diagnosis reasons, was going to take it out on the water and disconnect after it played up to see if problem persisted, however before i did that i also checked the spark plugs out of curiosity, plugs were all good but only had L78C champion instead of QL78YC (suppressed plug), after reading threads on the possibility of non suppressed plugs tripping the slow mode, i thought what have i got to lose.
Fitted the correct champion QL78YC in and problem is all fixed, sounder is a hell of a lot cleaner and idles and runs like a dream, idled like a bit of **** before! So before you go replacing the expensive bits always pays to start with the basics, im a mechanic and have never seen a cdi unit play up due to RFI, my jaw is still on the ground, bloody electronics!
hope this saves someone a lot of grief one day
 
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