squeezing more power out of a 25hp merc?

[JMichael]

I am going to call Fred tomorrow and order a new intake impeller. I am ordering a tiny tach to make sure I dont blow the motor up.

I've thought about buying one of those several times but every time I think about the fact that you can't replace the battery in them and they're worthless after it dies, I decide against one. I have seen a clone of the TT then I'm considering now though because you can replace the battery on them.

 

[Lil' Blue Rude]

I am going to call Fred tomorrow and order a new intake impeller. I am ordering a tiny tach to make sure I dont blow the motor up.

As long as the impeller is the same size that should have come in it your not going to have to worry about pulling to many rpm. It takes ALOT of power to pull a outboard jet past 6000rpm with the stock impeller. If a stock motor does pull past 6000rpm It's setup wrong. Past 6000rpm the impeller start to loose ground or I guess a better way to put it is it can keep up with it's self and it can't pick up enough water so even though your turning more rpm your not gaining any speed.
Any way shouldn't have to worry about blowin the motor up because of pulling to many rpm. But I can understand wanting to be careful with it too.

 

[gotmuddy]

I am going to call Fred tomorrow and order a new intake impeller. I am ordering a tiny tach to make sure I dont blow the motor up.

As long as the impeller is the same size that should have come in it your not going to have to worry about pulling to many rpm. It takes ALOT of power to pull a outboard jet past 6000rpm with the stock impeller. If a stock motor does pull past 6000rpm It's setup wrong. Past 6000rpm the impeller start to loose ground or I guess a better way to put it is it can keep up with it's self and it can't pick up enough water so even though your turning more rpm your not gaining any speed.
Any way shouldn't have to worry about blowin the motor up because of pulling to many rpm. But I can understand wanting to be careful with it too.

I am going to modify the timing and want to be careful. I am also going to lighten the flywheel.

 

[Lil' Blue Rude]

Be careful with timing because it's easy to get to much and have problems with detonation. I'd take it a degree at a time. That and the flywheel should be good for some more pep out of the hole. Be careful not to take to much off of the flywheel and make sure it's balanced afterward, don't want it coming apart. You might check with Chris Carson Marine to see about a set of reeds for it. That sould help it out with the low end some more.

 

[gotmuddy]

Be careful with timing because it's easy to get to much and have problems with detonation. I'd take it a degree at a time. That and the flywheel should be good for some more pep out of the hole. Be careful not to take to much off of the flywheel and make sure it's balanced afterward, don't want it coming apart. You might check with Chris Carson Marine to see about a set of reeds for it. That sould help it out with the low end some more.

I have been talking with a guy that races these motors, he suggests using stock rubber coated reeds.

 

[Lil' Blue Rude]

The reeds cages should be rubber coated not the reeds them shelves. Reeds are cheap and if they don't work you can always but the steel reeds back in.
One thing I've learned since I've been working on hot rodding my motor is what works for one might not work for another so try it yourself that way you know if it works for you. Don't mean that in a smart way either, I've just done things that wasn't suppose to help and they did.

 

[gotmuddy]

The reeds cages should be rubber coated not the reeds them shelves. Reeds are cheap and if they don't work you can always but the steel reeds back in.
One thing I've learned since I've been working on hot rodding my motor is what works for one might not work for another so try it yourself that way you know if it works for you. Don't mean that in a smart way either, I've just done things that wasn't suppose to help and they did.

I haven't decided how far I want to go with this motor. I am one of those poor souls who absolutely cannot leave something alone. I am kicking around the idea of a new jet pump. I think there is a way to get more power to the water with a different design on a pump.

 

[Lil' Blue Rude]

I know what you mean about not being able to leave something alone. As far as I know they don't make any other type of outboard jet pump. What do you have in mind for a new jet?

 

[gotmuddy]

I know what you mean about not being able to leave something alone. As far as I know they don't make any other type of outboard jet pump. What do you have in mind for a new jet?

I dont know if anyone has done this but I was thinking of having a small, simple gearbox to turn the power 90 degrees then use a impeller setup just like a current jet. the inlet would rap around the gearbox. My theory is the water won't have to turn which loses your power.

 

[Lil' Blue Rude]

Are you talking about something like an inboard jet? Straight in then straight out the back? Don't know how much it would help out taking the bend out. Be interesting to see though.
Only other jet that I can think of is a durajet but it can't run as shallow as a outboard jet. I don't kno wif they will run much shallower then a prop.
If you want to improve your pumps effeincy you can bevel the leading edge of the liner (wear ring). You don't want to go to far up, just about to the edge of the impeller blades. Not gonna make a big diffrence but if you gotta lathe it would be easy enough to do and enough small things will finally make a noticble diffrence.

 

[gotmuddy]

Are you talking about something like an inboard jet? Straight in then straight out the back? Don't know how much it would help out taking the bend out. Be interesting to see though.
Only other jet that I can think of is a durajet but it can't run as shallow as a outboard jet. I don't kno wif they will run much shallower then a prop.
If you want to improve your pumps effeincy you can bevel the leading edge of the liner (wear ring). You don't want to go to far up, just about to the edge of the impeller blades. Not gonna make a big diffrence but if you gotta lathe it would be easy enough to do and enough small things will finally make a noticble diffrence.

I will do that when I get a new intake.

A little update: I checked my compression today and it is 115-120psi. I found that mercury offers a .030 piston for a '96 model. Would it be worth my time to bore it? Also, my liner/ impeller are wore enough that with all the shims on top of the impeller I have a 1/8 of a inch clearance or more, that would likely kill my thrust wouldnt it?

 

[Lil' Blue Rude]

You probably won't see any gains from rebuilding the motor since there is only 5psi diffrence. You could do a leak down test. I think as long as it under 10% it's fiine. A new impeller and liner would probably help out some, not sure how much thrust your losing but I'd say it is.

 

[gotmuddy]

yesterday afternoon I put a fresh coat of jb quik weld on the liner and smoothed out the leading edge of the impellor. I noticed the boat planes alot faster.