johnson speed and performance

[allen.wood]

I have a 1970 Johnson 25 h.p model number: 25r70, mounted on a 15' 42" wide flat bottom alum. Currently it runs at 16mph (from gps) with me and gear about 300 pounds or so and still runs a bout 16 with another passenger and more gear. The motor runs strong and has had carb rebuilt and adjusted and new carb kit. Spark is good motor doesn't spit sputter or hesitate it sounds like it is new. The cavitation plate sits lower than the bottom of the boat because the shaft is 17" not 15" as this is a older motor I have been told the shafts were longer but that it is a "short shaft" motor. The transom on my boat is 15", I have put a 1x4 under the motor but that's as high as I can go. Currently the cav plate is about 2 inches under the boat. I have not checked compression I plan on doing it tomorrow, I'm sure its pretty high considering the age of the motor. I don't know what the pitch of the prop is im sure either a 9x10 or 9x9 don't think there are many options, prop seems to be in good condition no knicks and is not bent. Throttle does open up all the way so not a linkage problem. I know this is somewhat of a long post, just curious to see if it could be something I don't know about or if its just the fact that its almost a 40 year old motor, which I can accept!

 

[tashasdaddy]

Re: johnson speed and performance

your motor is set up properly for that motor and transom. i don't think you can expect more out of it. it is pushing a barge. the horse power is rate at the head on that motor, comparing it to todays motor rated at the prop, it equates to about an 18 horse modern motor.