HELP!!! Crank no start only in water

[hollywoodhale]

ok guys new to this and needing some help. 70 hp 3 cyl johnson j70tlcdc got it a few months ago ran it on the lake a few times very hard to start and will die if you let it idle. will run fine if you bump up rpm's even in gear past idle it runs great all the way up to WOT. runs and idles perfectly on the muffs at the house. drained fuel out and put in new premix [previous owner had already removed VRO pump] have replaced all fuel lines, new fuel pump, rebuilt carbs. compression on all three cylinders is 110 spark will jump 7/16 gap. running out of options not sure where to go next I do have a manual im not very impressed with. does not get into very good detail. im sure i have a spark advance problem but not sure how to dial it in. any help would be greatly appreciated. thanks in advance.

 

[racerone]

It only sounds perfect to you on the hose.------The motor does not have to do any work even when in gear.--------Have you checked flywheel key ?-------Looked at the reed valves ?---My tester would show 140 psi on a good motor like that.

 

[joereeves]

On a flushette, the idle should be set to 1000 rpm for a 20" shaft model... 1200 rpm for a 25" shaft model. The idle will drop to normal when in the water.

This is assuming that you have normal compression, spark, and clean carburetors... in general, all is as it should be.

 

[phillnjack]

110 compression is very poor
by that number it a 1986, is that a 49 cu in or 56 cu in ?.
I have a 56 oval port 1995 shows 145-147-145 on a cold cranking speed, if warmed up it goes higher by around 4pi per hole.

maybe you need a tin of powertune to get rid of a bit of carbon in the ring grooves and bring compression back up a bit?