yamaha 15 hp 2cycle power loss

[billisherwood]

3 yamahas with the same problem loss of power 4year old engines. Dingy won't get on plane unless I lean forward for about 2-3 minutes. Then it runs fine. I have cleaned carb. many times,changed gas tank, replaced coils, fuel line, fuel filter, gas, plugs, installed carb. repair kit. It used to be that if I took the cover off it would get on plane much quicker. 2 othe boats here with same problems. Dolfins helped on one but did't cure the problem. It feels like it is a fuel problem but don't know what to thy next.<br />Any suggestions?

 

[robards]

Re: yamaha 15 hp 2cycle power loss

How are the boat bottoms, painted? Slime? Barnacles? Props ok?

 

[billisherwood]

Re: yamaha 15 hp 2cycle power loss

bottoms clean, props almost perfect. I today put the gas line directly on to carb also service manager in States recomeded spraying gas or starter fluid into intake while under full load to see if it not getting enough fuel. The engine quit or slowed down when I did that. The plugs are wet when I stop after not getting on plane. Thanks, bill

 

[robards]

Re: yamaha 15 hp 2cycle power loss

Are the motors mounted to low? Causing too much drag, because of the leaning forward thing? Cav. Plate should be 1" below bottom of center of boat? I have seen them run a little lower but depends on the boat..

 

[rodbolt]

Re: yamaha 15 hp 2cycle power loss

wow instead ofd all the parts playing has it ever dawned on anyone to run it on a test wheel?<br /> thats why they make them.yb1619 wot 500-5200 rpm. if it makes it its not a motor problem if it does not it will allow stationary testing. what could be more simple ?<br />and has anyone inspected the pump diaphram for leaks ?

 

[billisherwood]

Re: yamaha 15 hp 2cycle power loss

Motors are mounted at the right height 1" below bottom. 1 is on a 12' carolina skiff another on a 10' caribe inflateable. I don't know what a test wheel is. The 2 diaframs in the fuel pump are clean and whole. No pin holes. I have even gravity fuel fead the motor. Thanks again, bill (no spell check)

 

[rodbolt]

Re: yamaha 15 hp 2cycle power loss

with 3 of them with the same problem you will be money ahead to purchase the test wheel.<br /> its a serious time saver and does not require idleing in and out. just place the test wheel on and submerge the gearcase in the water. then WOT runs are possible. you will need an inductive tach capable of at least 10K as the system uses a waste spark on most tiny mites.

 

[billisherwood]

Re: yamaha 15 hp 2cycle power loss

Being in tht Bahamas 350 miles SE of Miami a test wheel isn't available but thanks for the thought. bill

 

[jasell]

Re: yamaha 15 hp 2cycle power loss

You said it used to work better with the cover off.<br />Could it be a cooling problem?<br /><br />You got the engines for three years or more, have you change the impeller in the water pump during this time?<br /><br />I once tried to fix an old 2-stroke which had no power, no matter how much throttle I gave it just idled. The impeller was grudge and the cooling channels in side was filled with corrosion, we replaced it with a 15 hp yam which have worked perfect ever since (6 years now).

 

[rodbolt]

Re: yamaha 15 hp 2cycle power loss

ISH<br /> if I could get one sent to me in Rio Chico Venezuela I will bet you could get one in the bahamas. it did take a bit and the shipping was pricey but I got one for the v4-v6 yam while I was down south. if everything else is fine its possible that carbon has built up in the exhaust and is caausing a power loss. have the motors ever been decaarbed and do you use ring free? its rare to see that much carbon unless its a commercial use engine but it is possible.<br /> also when ya did the fuel system did you do it all at once or over time? a carb rebuild with poor fuel means another carb rebuild.

 

[billisherwood]

Re: yamaha 15 hp 2cycle power loss

Having the cover off doesen't work anymore. The impeller is fine I even took the head off and all the passages were clean with no carbon build up on the head. In fact the head very clean. I'm thinking air leak or reed valve problem although when it is trying to get on plane the plugs are wet. I trying to get a local OB mech. to look. thanks again for you ideas. Ish

 

[rodbolt]

Re: yamaha 15 hp 2cycle power loss

when you did the carbs did you rebuild the fuel pumps as well ?<br />a reed problerm usually shows up as blowback from the carbs.

 

[billisherwood]

Re: yamaha 15 hp 2cycle power loss

To Kitty Hawk NC, The fuel pump is apart of the carb.. It had 2 metal reeds and 2 diaframs everything is clean and fits well with no pinholes in the diaframs.<br />The service manager of a large dealership I talked to in Ft. Lauderdale didn't think it was a fuel problem when I discribed spraying spraying starter fluid in the intake when the motor was under load and wideopen. He can,t figure it out either as discribed everything I have tried. There is no blowback from the carb. Thanks,

 

[rodbolt]

Re: yamaha 15 hp 2cycle power loss

I am aware the pump is part of the carb. I am also aware that the pump parts are not included in the carb kit and often get overlooked. a leaking diaphram will cause an excessivly rich fuel mix. it will first show up as a sluggish engine, spraying fuel or starting fluid in a rich engine will only make it run richer and worse. with no carb blowback I would not look at reeds to hard. I would test the output of the CDI as well as the coil secondary KV output. a weak ign system will cause wet fouling as well. be aware that most service managers I run into have no clue how to actually fix the motor and quite a bit of them guess.so while its good to ask be careful when getting answers.that 15 works exactly like a 200. it sucks ,squeeze's, bangs and blows. if it cant do it all at the correct time in the correct proportions it does not run correctly.

 

[billisherwood]

Re: yamaha 15 hp 2cycle power loss

thanks, Kitty Hawk, i will look at th weak ign. sys