55HP johnson won't go above 1/3 trottle

[cstoliker]

I have a 1968 Johnson 55HP 3 cyl, with a capacitance discharge ignition. It was running fine a few months ago but now if I give it any more than about 1/3 throttle the motor looses power and won't accelerate. I replaced the Points,coil,powerpack, fuel pump and had all three carbureters cleaned and rebuilt. I checked the timing and cylinder compression. This motor should be going like a bat out of hell, and anything I thought could be causing this problem has ether been replaced or rebuilt. the motor idles nice and runs great at low speeds. I have no idea what to try next

 

[stairliftoheaven]

Re: 55HP johnson won't go above 1/3 trottle

have you tried pumping primer bulb while trying to accelerate? also how about fuel filter and is your tank properly ventilated?

 

[cstoliker]

Re: 55HP johnson won't go above 1/3 trottle

I have tryed that, and spraying premix directly in the carbs.

 

[real550A]

Re: 55HP johnson won't go above 1/3 trottle

I'm having exactly the same problem with my '75 Johnson 25h.p.! Also, have sprayed in carb with throttle wide open on boat. No difference.<br />New fuel pump, tank and hose that work on another motor. I can only think reeds are cracked, or debris under them? 100 lbs. on each cyl.<br />HELP!!

 

[papasage]

Re: 55HP johnson won't go above 1/3 trottle

have you changed plugs . they might look good but want fire under compression . check gap .

 

[real550A]

Re: 55HP johnson won't go above 1/3 trottle

Yes, I have tried 2 sets of new plugs, also.<br />Thanks for your help!

 

[cstoliker]

Re: 55HP johnson won't go above 1/3 trottle

Yes tryed new plugs and I get 137lbs on eatch of the 3 cly exactly. If the reeds were damaged in some way wouldn't the motor backfire through the carbs or run ****ty? It runs fine at low speeds.

 

[real550A]

Re: 55HP johnson won't go above 1/3 trottle

I may have found a clue! Upon removing the flywheel, I noticed some oil residue around the points. A closer look makes me suspect crankshaft seal. I think that's my culprit, as that would certainly explain good slow speed operation and poor high speed. Does this make sense?

 

[cstoliker]

Re: 55HP johnson won't go above 1/3 trottle

real550a: let me know if fixing ur crankcase seal helps U, I dont see any leaks on mine but if It works for U maybe I will have a place to start looking.

 

[real550A]

Re: 55HP johnson won't go above 1/3 trottle

I'll sure let you know. Should be running by Fri. or Sat. I don't have much time to work on it before then.

 

[real550A]

Re: 55HP johnson won't go above 1/3 trottle

After replacing the top crankshaft seal, motor achieves a full 1000 rpm more at WOT in the tank with test prop. I can't boat test 'til end of the month, but I'm thinking this was it.