73 Johnson 65 hp Won't Plane

[tunnelking]

Hey Guys, I own a 73 Johnson 65hp and run it on a 1974 regal runabout. Up until yesterday the thing ran great. 35mph all day long, and it really did not have any trouble getting there. While I was towing my buddy i was gradually increasing throttle to gain extra speed and as soon as I got to full throttle the engine lost all power and died. It started back up with no real trouble but now the dang boat won't even go 5mph. The engine seems to run just fine with the muffs on seems to react very well when throttle linkage is advanced. The prop spins fine when engaged in gear and the engine even seems to get to full power while in gear UNTIL THE BOAT GOES INTO THE WATER. Then it is lifeless. Puttin around at 3mph with no chance of creating a wake, but if all weight (about 325lbs) is moved to the bow then we can get up to around 11mph in 2 minutes or so. Anyone wanna come out and join us for some fun in the sun.. This sucks.... Anyhow, where do i begin. I explained the symptoms to a guy I know and he mentioned something about the stators being bad or something. Whatever it is is a bummer so any and all help is going to be greatly appreciated. thanks

[Joe Reeves]

Check the compression. It should be 100+ psi and even on all cylinders. What readings did you get?With the s/plugs removed, check the spark. It should jump a 7/16" gap on all cylinders with a strong blue lightning like flame.... a real SNAP! Does it?If the above checks out okay, possibly you bought some water with your latest gasoline purchase? Also, check the linkages on all three carburetors to make sure that the throttle butterflies are wide open at full throttle (engine not running of course when checking).Spark plugs should be Champion QL77JC4 plugs, gapped at .040 .

[tunnelking]

Hey Joe! Thanks for the quick reply. I did (because of this problem) just purchase a new fuel tank and fuel line. The old one was very old and upon inspection of it there was some pretty flakey black junk floating around in there. We checked the fuel filter and it seemed fine, so the flakes were of little concern. I did just buy 3 new plugs today. they did not have the Champion but they did have the Autolite equivilant And it is the QL77JC4. I will check the gap. I am going to run out and pick up a compression tester and a spark plug guage. The carbs were rebuilt last year I believe and they look fine and all valves seem to work perfectly. I will get back to you on the spark and compression tests. Thanks again for the reply

[tunnelking]

Hey Joe, I checked the spark and compression and I think we have a clue. The spark is fine but the compression is crazy. top= 0(zero)psi

[tunnelking]

Hey Joe, I checked the spark and compression and I think we have a clue. The spark is fine but the compression is crazy. top= 0(zero)psimiddle= 120psibottom= 130psiengine will idle on only the middle cylinder but won't idle on only the bottom one. I noticed a little oil sitting outside of the spark plug port for the bottom cylinder. thanks again for your help

[Joe Reeves]

Remove the cylinder head in order to inspect the piston, cylinder wall, head, etc. The "0" compression indicates (usually) that a major overhaul is required.

[tunnelking]

OK Kinda figured that this would have to happen. Thanks for the input and as things arise i'm sure you will here more from me reguarding this.

[JesseNKim]

hey man i had the same problem with my 73 65hp johnson i had 0 psi on # 3 cylinder upon further inspection the # 3 piston had ring failure and beat the rings to death on top of the piston it cost about 1000 to have rebuilt but in my mind the 73 or 74 models of these engines are better to rebuild than buy new they dont make them like they used too

and yes will run fine out of the water but under load poof nuttin and sometimes will pick up and go lol this is because of fuel building up in front of piston creating pressure to run the engine like a compressor lol