Evinrude 15HP will not Rev to WOT rpm low power

[flexfanac]

Re: Evinrude 15HP will not Rev to WOT rpm low power

I got the tach from amazon

Any thoughts on a semi-V hull vs a flat bottom because I have a link to a guy that put a 15 carb on his 9.9 and even with 540lb he was able to get 22mph. with 270lb=24.6mph
Even with the stock 9.9 his performance was much better than i am getting.

youtube search= "Speed Test Johnson 9.9"
http://www.youtube.com/watch?v=7D0_szcNa6Q&feature=relmfu

youtube searc= "Speed Test - Johnson 9.9 to 15 hp Conversion"
http://www.youtube.com/watch?v=l-0AYuCCDBc&feature=relmfu

I know you cant believe everything you see on the internet but any thoughts. I would say my performance is very poor. Any crazy ideas why i might be a bit low on power? could it be from an air leak? would i hear it running rough? how about reeds?
Should I just give up and post in the prop forum?

Thanks

 

[davkrat]

Re: Evinrude 15HP will not Rev to WOT rpm low power

Having the exact same issue on my 14' Valco with a 1977 15 hp Evinrude: http://forums.iboats.com/prop-questions-topics/prop-1977-15hp-evinrude-2-cycle-635815.html

Did you ever figure it out? Thinking I may need to rebuild my fuel pump as I may be starving for fuel at WOT? Rebuilt carb no change, thinking of going with a 8 pitch prop. I have the exact same issue where the full throttle does not appear to open the plate completely I can push it another 1/4" than the cam roller and plate will.

Just like you watching guys get 20+ mph out of the same boat and motor drives me nuts LOL!

 

[racerone]

Re: Evinrude 15HP will not Rev to WOT rpm low power

Call around and see if there is a shop with a test propeller.-----It is used to determine the power output of the motor.------Will tell you if the motor has problems or whether it is the boat set-up.---The rest is just guessing !

 

[oldboat1]

Re: Evinrude 15HP will not Rev to WOT rpm low power

that motor is rated at about 4800 rpm at WOT, isn't it? If the carb is leaned out properly when set on boat at or near WOT, that might be about it. If the motor bogs when you enrich the mix, as you initially noted, you probably have the high speed setting about right.

doesn't seem like a good idea to run more rpms than the rating, so would want to be sure that 6000 is within the range god and Evinrude intended.

 

[racerone]

Re: Evinrude 15HP will not Rev to WOT rpm low power

These carburetors are equipped with a fixed high speed jet !------The 15 HP model is rated at 6000 RPM

 

[davkrat]

Re: Evinrude 15HP will not Rev to WOT rpm low power

My 15 says 5500-6500 rpm.

 

[oldboat1]

Re: Evinrude 15HP will not Rev to WOT rpm low power

test prop seems like a good idea. would permit analysis of the motor, without added boat and hull complexities. 50:1 fuel mix.

 

[racerone]

Re: Evinrude 15HP will not Rev to WOT rpm low power

Correct, rated at 6000 RPM and wide open throttle range is 5500 to 6500 RPM.-------It should be obvious that a motor run at 6500 rpm will not live as long as one that rund at 5500 rpm.

 

[tomhath]

Re: Evinrude 15HP will not Rev to WOT rpm low power

Correct, rated at 6000 RPM and wide open throttle range is 5500 to 6500 RPM.-------It should be obvious that a motor run at 6500 rpm will not live as long as one that rund at 5500 rpm.

That's probably true. But he should be aiming for 6000 with a light load; lugging with a heavier load is hard on the motor. By the way, did you verify the carb is correct? Someone might have swapped it for the smaller throat 9.9 carb.

For what it's worth, I have a 14' semi-v aluminum boat that goes about 16 MPH with a very good running 9.9 Johnson motor and 10" pitch prop right at 5000 RPM wide open and a light load.

The same boat with a 9.9/15 Evinrude (15 hp carburetor and 11" prop that were on it when I bought the motor) goes about 17 MPH. I haven't put the tach on the Evinrude but it didn't sound like it was running full RPMs. I expect with a 10" prop it will rev a little higher but still move about the same speed; might find out next Spring, but I'll probably sell the motor before then.

 

[davkrat]

Re: Evinrude 15HP will not Rev to WOT rpm low power

After Sea Foam (lots of chunky black carbon in the exhaust!), adjusting the armature cam out to open the throttle plate slightly more and rebuilding the fuel pump I got up to 5650 rpm and 20 mph with my 15 HP spinning a 10" pitch prop on my 14' boat. I really think the Sea Foam must have helped a lot.

 

[Hahn007]

Re: Evinrude 15HP will not Rev to WOT rpm low power

I am having similar issues but on a heavier boat.

How did you go about the "seafoam" procedure?

mixed in with fuel and/or sprayed directly into carb?

 

[davkrat]

Re: Evinrude 15HP will not Rev to WOT rpm low power

I bought a can of the standard Sea Foam that I mixed in a gallon of fuel and also a can of the Deep Clean aerosol. Ran the Sea Foam in the fuel which smoked a bit and then sprayed a bunch of the Deep Clean directly in to the carb while running. Really smoked then. I was not able to get to the lake to blow it out until yesterday so I just let it run at idle a few times and the goop coming out the exhaust was amazing. The carbon literally felt like chunks of sand suspended in vasoline slime. That stuff had to come from somewhere and I'm sure it wasn't doing me any good wherever it was.

 

[gabebp]

Re: Evinrude 15HP will not Rev to WOT rpm low power

Hello,

I'm new to the forum and was wondering if anyone had any more info on this rpm issue or if the original poster solved the problem. I have a 15 hp motor with the same issue on a 14' aluminum boat. Goes around 16 mph at 5,300 rpms. These should be north of 6,000. My sticker has this as the rated rpm for 15 hp. I tried reducing the prop pitch and it didn't improve the rpms. I have a digital tach and ran with the same load in the boat each time.

I took the carb off and it has been upgraded to a new plastic float and it looks great inside. The opening in the throat indicates this is a true 15 hp as evidenced by the 9/10" opening. I do think these 15s should push a light aluminum boat at 20 mph easily as evidenced by many other vidoes on youtube.

Wondering if the seamfoam treatment has more to do with de-carbing the cylinders?

Assuming the throttle plate actually gets to WOT (flat) and the spark is not the issue, is there anything in the "throttle timing" that could mess up the fuel air mixture at WOT? The throttle timing would not have a bearing on the max rpms as long as the mechanical linkage allows the throttle plat to open to wide open, correct?

Thanks for keeping this thread going!

 

[Acton]

Im also wondering if this issue was solved or if anyone has any input as I am also having the same issue....