New guy here OMC 25 Help

[arkansasbowhunter]

I have researched all the pages in this forum and read everything I could. I have purchased a new 1999 Johnson 25 electric start motor. I say its new as I know the owner and it has been garage stored and never in the water. I did some research on my motor and ordered a parts manual for the TE 25 30hp motors. The only difference that I could really tell is in the carbs. I bought a 30 hp carb and put it on but to no avail didn't see any increase in top end. I am currently running a 10x13 stainless OMC prop with a WOT of 5700 rpm's running 30mph via gps.

Am I missing any mods that would increase top end that can be done by a hobbiest. I know a little about motors. Are there any repair manuals to be recommended for this motor?

Thanks for any help.

I forgot to mention I have it on a 1542 aluminum boat.

[hebert51]

just get a mega 25.......

[arkansasbowhunter]

I have actually been looking for a suzuki dt25 and mega but cannot locate one. Anyone know of one I am interested.

[genea01]

I have researched all the pages in this forum and read everything I could. I have purchased a new 1999 Johnson 25 electric start motor. I say its new as I know the owner and it has been garage stored and never in the water. I did some research on my motor and ordered a parts manual for the TE 25 30hp motors. The only difference that I could really tell is in the carbs. I bought a 30 hp carb and put it on but to no avail didn't see any increase in top end. I am currently running a 10x13 stainless OMC prop with a WOT of 5700 rpm's running 30mph via gps.

Am I missing any mods that would increase top end that can be done by a hobbiest. I know a little about motors. Are there any repair manuals to be recommended for this motor?

Thanks for any help.

I forgot to mention I have it on a 1542 aluminum boat.

you need to find you a 35 carb and put on it they are the dame motors put after market reeds in it and shave the head to about 150 comp and run 93 octane gas and you can open the tuner a little that will get you headed in to a very good start

[arkansasbowhunter]

with so many 35 model carbs how do I know which model to purchase. what about the cam linkage does that need changed out too? thanks for help. just changing the carbs out how will that affect the top end? I didn't notice any difference going from 25 to 30 carb.

[genea01]

with so many 35 model carbs how do I know which model to purchase. what about the cam linkage does that need changed out too? thanks for help. just changing the carbs out how will that affect the top end? I didn't notice any difference going from 25 to 30 carb.

yes the 35 carb will help and the other things will help you do have to relise it is still a 2cyl motor so if you looking for 10 mph on ur boat going bowfishing u need to get a bigger motor but that 25 omc is a solid motor and the mega is a detuned 40/50 it is a strong motor and a very good one

[zul8tr]

I have researched all the pages in this forum and read everything I could. I have purchased a new 1999 Johnson 25 electric start motor. I say its new as I know the owner and it has been garage stored and never in the water. I did some research on my motor and ordered a parts manual for the TE 25 30hp motors. The only difference that I could really tell is in the carbs. I bought a 30 hp carb and put it on but to no avail didn't see any increase in top end. I am currently running a 10x13 stainless OMC prop with a WOT of 5700 rpm's running 30mph via gps.

Am I missing any mods that would increase top end that can be done by a hobbiest. I know a little about motors. Are there any repair manuals to be recommended for this motor?

Thanks for any help.

I forgot to mention I have it on a 1542 aluminum boat.

---------------------------------------------------------------------------------------

Using the following specs for the 25 Johnson:

http://www.piranha.com/motor_specs.php?id=4566

the gear ratio is 2.15:1. With a 13"pitch prop at 5700rpm you measured the theoretical speed (no slip and there is slip) is:

Max theoretical speed = 13" pitchx5700 rpm/(1056 convert factor x 2.15 gear ratio)

= 32.6 mph

If you are getting 30 mph the % slip is about 8%. That is darn good for your boat.

Of course there are many variables to consider. And a main one is the pitch of the prop. The formula assumes the average pitch of the prop which is usually close to a manufactures labeling. If a measured pitch by somebody than it probably will not be the average. How accurate is your tach?

You do not state how heavy the boat, motor, driver fuel and is and that will effecr speed and acceleration.

Note that the engine is rated at 5500 rpm so the motor is over reving so you can increase pitch or diameter or some of each to reduce rpm. Might also consider going to 6000 rpm and raise the motor on the transom to reduce drag. As you do that a greater pitch might prove better. The fine tuning is a trial and error process but you are close to the expected speed if you pitch, rpm and gear ratio are correct.

[arkansasbowhunter]

thanks for the info. I didn't know what kinda slip I was getting.

My boat has trolling motor, 2 batteries in back, 6 gallon gas tank full, 2 pedestal seats, gun box with aluminum flooring. Cannot give wt as I really don't know. It is a war eagle 1542. The specs give me hull wt of 290lbs. I am using a tiny tach to gauge the rpms of the motor. The prop is a factory omc 13 pitch is all I know about it. The boat planes very good and slightly porpoises. how else does one raise the rpms. I am thinking of getting a jack plate for i. I have the cavitation plate even with the bottom of the boat.

[50hptiller]

yes you need a jackplate, +3mph alone, 6 inch offset, and more pitch after the jackplate

[arkansasbowhunter]

what is recommended jackplate or pt130. I have heard from guys running the pt 35's that they aren't that durable.