'75 15 HP Johnson Seahorse

[Tim Wagner]

Re: '75 15 HP Johnson Seahorse

Well, I managed to sell my old boat and now Im getting this beast unwinterized.
So im back screwing around with the 15HP.
I got it running as of now but really havent done anything other than get it running.
I gotta get a wheel puller to get the flywheel off and check the points and timing.
For now though I can say with 100% positiveness that without the thermostat in it, the block stays cold to the touch.
I did order a thermostat and gasket but i got the incorrect gasket and for 2 bucks, screw it.
I made one from bulk gasket material.
Then the thermostat needs its own gasket (who freekin knew!!) so I cant use it.
Anyway, I went on to Crowley and ordered the parts from there. Thermostat, thermostat gasket and cover gasket.
Advanced didnt have Champions or NGK's, had to buy Autolites. Gapped at 0.30
Ill take note of the cylinder if it fouls.
I wanted to take it to Port Clinton this weekend but they were calling for 8-10 footers on Erie so the trip was officially cancelled.
I stayed home and monkeyed with that motor and cut grass (sipped a couple beers too)

 

[Tim Wagner]

Re: '75 15 HP Johnson Seahorse

Oh, forgot to mention.
The compression is 92lbs on both cylinders
Id like to check it again hot, but it never warms up and I had it running for a while.
The block stays cold and the tell-tale water is cold.

 

[Tim Wagner]

Re: '75 15 HP Johnson Seahorse

This thing is a money pit!!
Ok, put new plugs in it gapped to 0.030.
The theromstat is in also.
Took it out and it ran for about 2 hours.
Trolling at about 2900 RPM's (i have a tach I put on the crank there in the middle of the flyswheel)
I backed it down after about an hour and I heard it foul. I kicked back and ran on one cylinder like crap!!
By the way, the thermostat has made the block temp normal. 133 or 140 degrees.
Now, I put new plugs in it (yet again). I got NGK B6HS
I also pulled the flywheel and checked the points.
It looked brand new in there. The points were only set at 0.012. I double checked them it is so. 0.012
I did get my little point file and clean both of them up. They looked good but I did it anyway.
I reset them to 0.020 as stamped on the plate in there.
It runs in the barrel but now its not pushing anything out the tell tale blowhole. WTF??
Its pumping water cause the leg is full. Water is pouring out of the hole on the side and when i plug that one it pours out the one in the back by the shift rod.
Ill look into this but I want to blow all that carbon out of there.
im gonna put on my clover leaf lookin prop and run that thing at 6000-6200 RPMs for like an hour (if I can stand it screaming that long) I can check it with my tach to be sure where im at.
When I done there and while she's all warmed up, she's getting a generous blast of the power tune.
Oh, this time it was the top cylinder

 

[Tim Wagner]

Re: '75 15 HP Johnson Seahorse

Well the saga continues on this little money pit.
Had it out on Saturday and it ran pretty good for about 5 hours.
It never fouled a plug but something under the flywheel is bound up and grabbing on it.
Something on the timing advance. Once I pull the flywheel ill know more.
I did have my cloverleaf prop on it to try to blow some of the carbon out of there.
Man it screams too, on my handheld tach right on the top of the shaft on the flywheel it measures 6280 RPM's and I get about 6.4-6.5 MPH out of it.
Update to follow.

 

[Tim Wagner]

Re: '75 15 HP Johnson Seahorse

Pulled the flywheel last night and found one of the 5 screws that hold the timing plate in place had backed itself out and was grinding on the underside of the flywheel.
I took out every screw one at a time, added locktite and put them all back in and torqued them as tight as I could.
Put everything back together and it fired right up.
At this point, I think my plug fouling problem was from being way over propped.
The RPM's never got up to anything close to the low end of 6000.
now with this prop (a 10P), im at 6280-6300 a WOT. The boat goes about 6.5-6.6 MPH.
I might be in business, unless it decides to detonate and throw a rod through the cowling.

 

[Tim Frank]

Re: '75 15 HP Johnson Seahorse

Don't forget the Champion plugs....you shouldn't need a hotter plug running at that RPM.

 

[ONERCBOATER]

Re: '75 15 HP Johnson Seahorse

i am trying to figure out how your running over 6k RPM on a 10 pitch prop.... on a largish boat. I have a 12ft jon boat with an 1983 version of that engine.... and with a 9.25 x 10P stainless or aluminum (ran both) i don't quite achieve that rpm (25+mph)... and I am running just over 130PSI compression.

Sean

 

[Tim Wagner]

Re: '75 15 HP Johnson Seahorse

i am trying to figure out how your running over 6k RPM on a 10 pitch prop.... on a largish boat. I have a 12ft jon boat with an 1983 version of that engine.... and with a 9.25 x 10P stainless or aluminum (ran both) i don't quite achieve that rpm (25+mph)... and I am running just over 130PSI compression.

Sean

The prop is one of them 4 bladed cloverleaf looking things.
It is a 10P and my handheld tach reads 6280 at WOT.
Im measuring on the shaft on the top of the flywheel.
You jam the cone shaped end of the tach in the hole on the top of the shaft.
It sounds like it too.
Loud and screaming. 6.6 MPH

 

[samo_ott]

Re: '75 15 HP Johnson Seahorse

Do you have a picture of that tach setup? I'd like to see if if you could post one. Thx.

 

[Tim Wagner]

Re: '75 15 HP Johnson Seahorse

Do you have a picture of that tach setup? I'd like to see if if you could post one. Thx.

Correction. its a 7P. My bad. I am an idiot on this one. Sorry for that confusion.
Youve been around the block I see per your rank and number of posts so I wasnt about to question you.
So last night I had a look at that rediculous prop and it is a 7P.
That motor is so loud though. I wish there was a way to tone that down or insulate it.

 

[kbait]

Re: '75 15 HP Johnson Seahorse

If your big motor is a 4-stroke, your normal sounding 15hp 2-stroke is extra loud by comparison!

 

[Tim Wagner]

Re: '75 15 HP Johnson Seahorse

If your big motor is a 4-stroke, your normal sounding 15hp 2-stroke is extra loud by comparison!

Its not a 4 stroke. Its a merc 125 that only runs on 2 cylinders under 2000 RPM's.
It trolls like a dream. Anyway, it is very quiet compared to the kicker.
I have roll of adhesive foam about a half inch thick and 4 inches wide that Im going to try to line the inside of the cowl with. Its pretty tight in there so it might not work. I dont want any rubbage.