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Hot rod 9.9 build up

Well, finally had the time to get out on the lake. I had found the break in procedure from Johnson. Did my 4 hrs idle in a tub in driveway. Then 30 min idle in drive. Got in 30 of 60 min at 3500 or less then rain was coming. So goosed it to get off the lake. From idle this thing certainly has some snap! Topped out at 20-21 mph. Stock was 12-14mph. My other 9.9 with the stock square tuner and the 15hp carb got 17-19. Might re prop as this one has some dings and has rock flexed the wrong direction since 75.....
 
Did some quick checks. Heard a rubbing sound. Looked like coil was rubbing flywheel. Backed coil off a bit should be ok until I can get a new plastic ring for mag plate. Both cyl at 100 psi. Will watch it, should climb as rings seat. Plugs are a red/brown color, running 25:1 XD-30 oil for break in. Idle is smooth once warms up, not as smooth as my 83 9.9. But trolled so low the boat hardly moved. Mid is smooth as well as high. No surging. Hole shot is vastly better than the other 9.9. Only annoying part is the exhaust relief hole noise trolling as I have the meg tuner in it. Other than that it is nice. I will type up a full list of what mods were done tomarrow. Time for bed.

P.S. Boat is a 12 ft Lund Car topper. Nice boat.
 
So what would you estimate hp? Did you make mods to the 15 hp carb? At least drilling some more holes in lower cowling for fresh air? I have made several 3/8" holes just under carb on almost all my 9.9/15's. You will get more out of this motor with Saber Amsoil @ 2 oz. per gallon. I'm sure your running 91 "clear" fuel, eh? How much did you shave off the head? With the tuner, you might get better hp with a little less prop?.....but not sure. Certainly wouldn't hurt to crank rpm's another 500....the newer Evin/Johnson.....probably 84 to 91, can spin 7000 no problem. What's your rpm now? What rotating assy did you start with. Think they made some upgrades in about 1984, but I'm just going on memory....not sure of exact date. One other tech mentioned it earlier in a thread, might have even been THIS thread. Anti cavitation plate is about even with lowest point on the transom....or even 1" above?
Since you know you're not going to be hitting anything you can go ahead and knife edge that prop and skeg too.
 

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timguy said:
So what would you estimate hp? Did you make mods to the 15 hp carb? At least drilling some more holes in lower cowling for fresh air? I have made several 3/8" holes just under carb on almost all my 9.9/15's. You will get more out of this motor with Saber Amsoil @ 2 oz. per gallon. I'm sure your running 91 "clear" fuel, eh? How much did you shave off the head? With the tuner, you might get better hp with a little less prop?.....but not sure. Certainly wouldn't hurt to crank rpm's another 500....the newer Evin/Johnson.....probably 84 to 91, can spin 7000 no problem. What's your rpm now? What rotating assy did you start with. Think they made some upgrades in about 1984, but I'm just going on memory....not sure of exact date. One other tech mentioned it earlier in a thread, might have even been THIS thread. Anti cavitation plate is about even with lowest point on the transom....or even 1" above?
Since you know you're not going to be hitting anything you can go ahead and knife edge that prop and skeg too.
Click to expand...

Hey Tim, no mods to the OMC 15hp carb.
Black airbox is still stock. May drill some holes, did that to my Stihl ms170 and it helped a bit.
Running 25:1 XD30 oil on 91 non-alc non-oxy fuel for break in, have 5 more hours per the manual. Will switch to a better mix after break in is done.
Shaved .008" off both head and block to get them flat. Did it on a Bridgeport mill. Both were cupped opposite of each other. Clay on piston top said .045 clearance. so left it as good.
I am not sure what my RPM's are, have yet to install a mini tac. But they sound higher.
Started with the 1975 power head. Same basic guts, new pistons with bigger wrist pin bearings.
Cav plate is level to 1/2" high right now. Every now and then I hear open exhaust so I don't dare go any higher. I welded a bung on exhaust cover for a pee tube, so I know it has water.
I need to rally all my mods into one post for ease of reading...... too many projects. Finally got a cyl for the 1932 Johnson OK-60...........
 
So the 81 and newer, have the larger pins allowing 7000 rpm? That's really cranking for a 2 stroke outboard......that's 233 fires PER SECOND, with a twin cylinder. These little sweeties are tough motors. They have been the standard, go to, must have motors at both our remote camps in Ontario. I have often run 3 of them side by side, when freighting. Got a few at home too...really love em, lotsa "kick" in a small compact and reliable package. Center leg, (exhaust housing), rests cleanly and comfortably on your shoulder......perfect for portaging and carrying around.
 
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