Re: 1984 25 hp johnson
Hey guys im new to posting on this site, but i just bought an 84 25hp johnson for a $100.00 I really just needed the botom end for my 20 hp johnson. The guy i bought it off said the powerhead was siezed. I took it home and tore into it. Removed the cowel, grabed the flywheel and tryed to turn it. To my amasement it wasmt siezed at all but somthing else was keeping the engine from turning freely, it sound like sand and rubber grinding together. I figure its the impeller hopefully if i get it running ill need some input on the 35 hp conversion. I would love to hang a 35 on the back of my gutted runabout crestliner. Turn it into a sleeper
Regarding the conversion:
I've done this on my 1982 25hp Johnson. After carefully comparing the parts numbers for 25 and 35hp models of the same year, I realized that the only difference in the powerhead was the carb. Same intake manifold, reed valves, and exhaust. These other parts may be affected for other years but for the 1982 models they were not. I think these additional parts do add some power - they seem to come into play when the HP rating point shifted from the powerhead to the prop.
The upgrade gave me about 2 mph of additional top speed, but the real improvement is in accelleration. The 25 was pretty slow to get on plane with 3 fishermen aboard, but the 35 pops up much more quickly. I've also noticed a small increase in fuel consumption, but it's still not a real fuel hog.
Mine did have some parts differences in the lower unit between 25 and 35hp. Main difference is that the 25 has a split gearcase and the 35 is a single piece. I was a bit concerned about the lower strength of the split gearcase, so I was very cautious during my first couple of runs, but it seems to be holding up just fine. I don't slam it into gear and prefer to gradually roll on the power while accelerating, which is probably good practice anyway.
