Johnson 225 HO problem

[grak]

Have 2000 Johnson 225 High output. The engine is not putting out full power at WOT. I can get about 5300 rpm's with a 131/2, 25 pitch four blade prop, and the GPS speed is 57 mph. I know several other people running the exact same boat and engine getting 5700-6000 rpm's with a 26 pitch prop and a GPS speed of 73-78 mph with about the same engine hieght as mine. <br /><br />The compressions are all between 95-92, spark to all cylinders, including at higher rpm's (though it was not checked under a load.) Every cylinder produce a rpm drop when the lead was pulled.<br /><br />what are somethings I should check. Could it be fuel related? Timing? Carb trash? need help, I'm missing 600 rpms and 15-20 mph.

 

[rodbolt]

Re: Johnson 225 HO problem

first thing is to run it up on a dyno or a test wheel to seperate engine problems from hull or prop problems<br />good luck and keep posting

 

[grak]

Re: Johnson 225 HO problem

If I run the engine on a dyno what amount of HP should it read. The Johnson 225 HO, should produce 247 shaft hp, should I be looking for a measurement around that value?

 

[rodbolt]

Re: Johnson 225 HO problem

hello<br /> it should make about 225HP plus or minus about 10%. most dynos have the specs in the operators manual and I believe OMC made a test wheel for it.<br /> also use a known good inductive pickup tach. would not be the first boat tach I ever saw that read wrong.

 

[Dhadley]

Re: Johnson 225 HO problem

I'd go buy whatever prop they have.<br /><br />Youre at about 16 -17% slip with your prop. Not great but not bad. At 6000 they are at between 2 and 8%. Thats fantastic. Almost unbelievable.<br /><br />You can improve your situation I'm sure. Do you have a jackplate? Have you tried raising the motor?

 

[grak]

Re: Johnson 225 HO problem

Thanks for the replies. I had the engine put on a dyno today. The tech said it was producing normal HP. I change the prop just for testing, from a 25 pitch 4 blade to a 24 pitch 3 blade. The rpms did NOT change still at about 5200-5300 max. The speed with the 24" prop increased about 3-4 mph at 60-61 GPS. <br /><br />The lower unit is not the original. Powerhead is a 2000, the lower unit a 1999. The tech said that should not be a problem. I have the opporunity to change to a omc "lightning" gear case, is that a good case? I know they were offered as an upgrade on the Johnson 225 HO. <br /><br />As far as engine height. The prop shaft is 3<br />1/2 inches below the pad with about 20 psi of water pressure. I don't think I can raise it much if at all. I had it at just over 3 inches, but water pressure was getting low at around 15 psi.<br /><br />As far as prop slippage how can you figure that? Plus, why would the 24" 3 blade run at the same rpm as the 25" 4 blade. They were different brands, the 25 was a renegade the 24 a raker. They didn't have a 26" raker for me to try.

 

[grak]

Re: Johnson 225 HO problem

Tryed several different props. Fastest prop ended up being a 27" shooter 4 blade.<br /><br />Here is the weird thing. Motor turn the 24" raker, 25" renegade, and 27" shooter at 5200-5300 rpm. No rpm change with the different props,Why? Is there anything else that I can try to get that those last few hundred rpm's.<br /><br />with the shooter the boat is going 68 mph. This same boat and motor should hit 72-76 with the right setup.

 

[Dhadley]

Re: Johnson 225 HO problem

Is the tach an E/J tach or some other brand? Is it set on position 6? <br /><br />Do the other boats like your have a jackplate?<br /><br />The Lightning gearcase is what should have come on an HO. If you have a chance to get one back on there, I'd do it.