Tweak my 25HP Johnson OB-

[Lund AnglerMJ]

i'D like to get some more out of my 25 HP outboard.I looked in the owner's manual, and it seem's only RPM's are different,in the 25 or 30 HP model's.It has fixed jet's,so how do I do it?I'm not very astute at the moter game,and it's a 99 TEL- Electric start model.Anyone help me out? Thank's,and see you on the water!

[KP]

The HP tweek is not only a change of jets. There timing and possible cam shaft changes required too. Rather than getting yourself into REALLY expensive and risky motor mod work, maybe you should try different mounting solutions on your boat. You can raise your motor 3/4" or 1 1/2" higher on the transom which reduces drag and increases RPM's and speed. It's best to have a tachometer and know what the max WOT range is on the motor. That way if your RPM's increase above the max WOT RPM, you add one pitch to the prop which will produce additional speed. I picked up 5 MPH doing that to my 30 HP motor. There's plenty of past posts you can search in the archive regarding "Raising the motor".

What kind of boat do you have? What's your current prop size and pitch? Do you know what RPM's your turning now? What is that motor's max WOT RPM range?

Shifting weight around in the boat can help performance too.

[Lund AnglerMJ]

Thank's for the response to my post. My boat is a Lund;Angler,16' 3", and is approx. 715 lbs.Of course I'v only got a few tackle box's,and you know the list. My prop is 10x13,and the RPM'S are 4500-5500 full throttle.I've talked to a gut who had his small motor go to 15HP from a 9.9;my manual has the 30 HP spec's with 31.8 cu engine. The only difference is an RPM of 5200-5800 range for the 30HP.If I can get the RPM range,can I achieve that 30HP output? My friend tell's me that the work was minimal to his 9.9 and that a different prop would help. What is the next size to move up to?Thank's KP,I really look forward to your response. (KP isn't a Military refrence,is it?)LTN- laugh through nose.

[Wally Walleye]

I did that to an older 25. If I Remember right you had to get a different carb, a new intake manifold, and the part that advances the timing. Your best bet is to get the PARTS manual and then you can compare the two. If my memory serves me that manual covered the 20,25,30 and 35. There were a few more parts needed to go from 25-35 and at the time it didn't seem worth it.

Wally

[KP]

That's definitely a heavy boat to push with a 25 HP and 5 additional ponies still makes it significantly underpowered.

You'd be better off to use what you have as cost effectively as possible an save toward a 50 HP. Your goal for optimum performance of the boat and motor is to get as close to or equal to the max allowable WOT RPM which you indicated is 5500 RPM. Your best off trying to tweek the mounting of the motor and install a lower pitch prop. With the current 10x13 prop, I would guess your WOT RPM is probably reaching a max of 4500 to 4800 RPM. Is that what your tach reads?

The first thing to work on, if it hasn't been already, is raising the motor 3/4" (one bolt hole). This will increase your RPM by 100 to 150 thus increasing your speed with that prop. Raising 1 1/2" (two bolt holes) adds 200 to 300 RPM but I would try one hole first. The goal is to get the motors cavitation plate even with, or a little above the bottom of the tramsom. Raising the motor too high will cause your prop to wash out in turns and potentially over rev the motor.

If your still more than 200 RPM lower than the 5500 max, droping one pitch to a 10x12 prop will add 200 RPM's. A 10x11 prop will add 400 RPM. You may or may not get more top speed reducing the prop pitch but you'll definitely get better hole shot and put that motor in the RPM range it wants to be in.

Don't expect any huge difference in performance but I can guarantee a little more speed and much better hole shot with what you have.

KP is both of my middle initials. It's always been my nickname.

[Lund AnglerMJ]

Thank's KP and Wally. I've got to save for a new motor.No question about it,I'm underpowered.My boat achieve's maybe 25mph and it is slow.It's rated to a 50 hp motor,and I better get one. I will try the tactics you gave me,and see what it does. Thank's again guy's,see you on the water someplace!