25hp 2 stroke 3 cylinder Johnson

**speedfreak** · 07-22-2011

Tim,

Sweet! This is just like my 1996 OMC triple. As stated in the opening comments of this thread, mine was originally the 25hp short shaft version. As you know, they made this little triple in a 25 (short shaft) and 35 (long shaft), so we just converted my 25, using all stock OMC parts. We bored it .030" over the stock 35 and put a set of 35HP jets in it, about the only difference between them. Stuck a set of racing boyseen reeds in it. This is strong little engine, the torque is unreal, top end speed is lacking a little. I have had the oiling system removed. I haven't been able to really see what the conversion is going to actually do performance wise yet, I just got through the break in period (25:1) after the rebuild. It feels a lot stronger. I use it for hunting so I am trying to keep it as reliable as possible, but get everything I can out of it. That 2.15:1 gear ratio hurts me running against the 2 stroke 3 cyl Tahatsu's, Suzukis and Yami's down here with higher gear ratios. I'll get some data posted as soon as I get a chance to get back out on the lake with it. I'm currently running a 13 pitch stainless stock OMC prop. Toward the end of the break in period I was turning between 6050 and 6100 RPM's WOT, 32 MPH. I was just holding it there breifly. May get a little more out of going back to 50:1 and fresh set of plugs.

**Mark75H** · 07-22-2011

More oil produces more power. Use as much as you can for power.

**biggdave92** · 07-22-2011

the tohatsu and yamaha are 1.85. the zuki is 2.09. Where a hatsu or yami would be turning a 12p, that is about equal to a 14p on a zuki. you should at least be turning a 14p in the 6-6200 range.

work on your setup. get rid of any weight you can.

**JohnsonM50** · 07-22-2011

You can go to BRP parts catalogues for part comparisons theres exploded views # lists etc. The only likely reasons for gear options would be for hi altitude &/or heavy duty or ocean going. In all cases they would be lower speed - more power gears. Your close enough to make up the difference with a 'good' prop. Usually that's where you will find the most but in light of all you've done.. sounds good. The other motors mentioned are also awesome contenders.. to even up the score would be cool, to beat-em a great accomplishment.

Theres alot to speed gain, the weight & its distribution, motor setup, prop choice, hull type & condition, All things working together = sweet spot. Any one of them alone might be hardly noticeable. To know actual speed & rpm's is critical to testing also taking notes as to whats changed, run conditions & results. If you change too many things at once it will be hard to tell whats helping & what isn't. Good Luck

**14apache** · 12-05-2013

Originally Posted by speedfreak

Tim,

Sweet! This is just like my 1996 OMC triple. As stated in the opening comments of this thread, mine was originally the 25hp short shaft version. As you know, they made this little triple in a 25 (short shaft) and 35 (long shaft), so we just converted my 25, using all stock OMC parts. We bored it .030" over the stock 35 and put a set of 35HP jets in it, about the only difference between them. Stuck a set of racing boyseen reeds in it. This is strong little engine, the torque is unreal, top end speed is lacking a little. I have had the oiling system removed. I haven't been able to really see what the conversion is going to actually do performance wise yet, I just got through the break in period (25:1) after the rebuild. It feels a lot stronger. I use it for hunting so I am trying to keep it as reliable as possible, but get everything I can out of it. That 2.15:1 gear ratio hurts me running against the 2 stroke 3 cyl Tahatsu's, Suzukis and Yami's down here with higher gear ratios. I'll get some data posted as soon as I get a chance to get back out on the lake with it. I'm currently running a 13 pitch stainless stock OMC prop. Toward the end of the break in period I was turning between 6050 and 6100 RPM's WOT, 32 MPH. I was just holding it there breifly. May get a little more out of going back to 50:1 and fresh set of plugs.

How much does your boat weigh? Thanks Eric

**speedfreak** · 12-05-2013

Eric,

About 325lbs.

**Tim Kurcz** · 12-05-2013

Originally Posted by Mark75H

More oil produces more power. Use as much as you can for power.

Sam is very right about the oil...... We run 24:1 in my son's engine for general laking, 16:1 for hard running. Increasing compression will get you more power, but you need to increase octane with this mod. BTW: Don't worry about revs. The optical ignition system has a limiter set at 6750 (cannot be defeated). You can't hurt that engine so long as you're running lots of oil. Unless you're running long distances, run the short prop and spin it!

Tim

**speedfreak** · 12-05-2013

Tim,

Thought those optical ignition systems were limited at 6200 on these engines?

Shane

**Tim Kurcz** · 12-05-2013

Originally Posted by speedfreak

Tim,

Thought those optical ignition systems were limited at 6200 on these engines?

Shane

Pretty sure it's 6750, but doesn't matter, you can't hurt the motor.

Tim

**speedfreak** · 12-05-2013

Tim,

Got it. Im at 6200 WOT right now with mine GPS'ing at 37.5 - 38.0 MPH. Thats with a 14P SS powertech prop. I'm not quite to my magical mark of 40 mph, getting close.