1986 Johnson 20 - 25hp?

[bonz_d]

Wondering if anyone knows what the difference is between these 2 engines and how they get the extra 5hp. I've looked thru BRP site and compared parts and the only difference I can see is in the intake manifold. Same carb, leafplate, leafs, head, exhaust, gearcase and gears.

Looking for an engine to put on my 14' Sean Nymph which is rated at 35hp max and having not much luck. Though I have come up with the 2 1986 Johnsons. The 20hp is very clean, runs great and the price is terrific. Just not certain a 20 would be enough and the 25hp would put me at that 70% mark.

Hope someone can give some insight as I don't think this 20hp is going to last long.

 

[Chinewalker]

Yep, the intake manifold is the kicker. Easy enough to modify it. Some had a space in there that could be popped out. Some were machined with a smaller hole and would need to be opened up. For extra beef, you could add the 30/35 hp carb (bigger venturi bore).

 

[bonz_d]

Thanks again old friend.
Going thru BRP that manifold is the only difference I've found. Hadn't looked at the 30/35hp parts yet though I might. I still find it hard to believe that the manifold hole would make a 5hp difference if they both use the same carb and reeds.

 

[Chinewalker]

It's a restriction of the air flow through the manifold that does it. FYI - there MAY be a jetting difference between the carbs that doesn't show up in the parts listings. If you flow more air through the carb to draw more fuel, the jet must be able to feed it or you'll run lean.