Yamaha sho 250 4 stroke

[pappa pete]

Problem is this it's slow getting on plane no matter what pitch prop you put on it , only when its warm outside, 60 degree and up, if it's in the 50's it rockets out the hole, dont matter if motor is cold or hot, does it all day now we've bought to program to hook it to the computer and all perimeters at on the money, even changed the high dollar fuel pump at yamaha company tech suggested, stumped,

[billybob]

My opinion is, switch to a MERC. 4 blade big trophy, with PVS vents. Small or big hub, then adjust the vents, with the best vent plugs for your boat application. Yamaha will not tell you to use a MERC> prop.

[pappa pete]

Done tried that, it only does it when its warm or hot outside , even
a 24p trophy plus

[cali kid]

Problem is this it's slow getting on plane no matter what pitch prop you put on it , only when its warm outside, 60 degree and up, if it's in the 50's it rockets out the hole, dont matter if motor is cold or hot, does it all day now we've bought to program to hook it to the computer and all perimeters at on the money, even changed the high dollar fuel pump at yamaha company tech suggested, stumped,
Yamaha sets up their motors to meet emission standards, lean. The air temp sensor richens the motor when its cold, plus the air is more dense. The motor likes it. If you could get a little more fuel to it it would make more power. Raise the fuel pressure or try to get somebody like Simons motorsports to reflash the ECM if you want more power.

[Motv18]

Test the temp sensors including the intake air temp.

[cali kid]

Problem is this it's slow getting on plane no matter what pitch prop you put on it , only when its warm outside, 60 degree and up, if it's in the 50's it rockets out the hole, dont matter if motor is cold or hot, does it all day now we've bought to program to hook it to the computer and all perimeters at on the money, even changed the high dollar fuel pump at yamaha company tech suggested, stumped,
Has the motor always ran this way?

[pappa pete]

Have tested everything, all within spec, warm or hot weather it's a dog coming out the hole, real slow to rev, below 60 degrees it a rocket out the hole, still runs same speed on top end though, weird

[billybob]

OK This may be the problem. These have variable cam timing, on intake cam only. All the advanced, cam timing drops out by 3,500 RPM. It has a control valve for cams, that uses engine oil. It may be possible, that when oil is hot. It does not advance intake cams, enough or at all. Possible oil leak or dirty oil plugged up something. You should be able to see this on YDIS under acceleration only. If it only happens when warm, outside. That is what I would check next. The warm oil, maybe the cause. In cooler weather they only warm up at extended idle. Next time it is cooler, idle around awhile, & see if it makes a difference. The air temp. sensor may be out of range.

[pappa pete]

It doesn't make any difference with motor cold or hot, if the outside temp is 60 degree or hotter it's a dog coming out the hole, if it's cool outside its a rocket, have checked air temp sensors,,airflow, , all within rage

[cali kid]

It doesn't make any difference with motor cold or hot, if the outside temp is 60 degree or hotter it's a dog coming out the hole, if it's cool outside its a rocket, have checked air temp sensors,,airflow, , all within rage
How many hours? Could be something mechanical. I had a 300 run funny once, turned out timing belt was one tooth off. Does it make oil? Have you checked the stats?

[pappa pete]

Maybe 200, doent make oil, stat no, but they seem fine

[cali kid]

Maybe 200, doent make oil, stat no, but they seem fine
How many hours ago did the motor start running weak?

[Motv18]

retarded cams make more power unless it’s just to much, iirc though advance delete is a performance mod.

The thing getting me is 50* good 60* bad. That’s almost to close for normal problems. Like something is triggering overheat or other power reduction.

I would and do gree with physical issue but thoes tend to affect all temps.

Unless its its one of the piston meltdown models

[Capt.Insane-o]

Bad sectors in the ecu table maybe.