XO-66 Yamaha 250 2 cycle?

[gradywhite248]

Looking for advise. I have a 1999 248 Grady with a XO-66 250 2 cycle. The engine runs great at low to mid power and is really in great condition. The one item is if I'm running around any where between idle and 5200 RPM is all good. Full fuel with five people on board running around 30-33 MH. If I advance the throttle to full the engine bogs down? really don't run over 51-5200 RPMs. Fuel? Air?

 

[Parthery]

Any number of things come to mind....Low pressure fuel pumps....VST dirty...etc...

Max recommended RPM is 5500. Wonder if everything is running fine but you need less pitch (more prop) to get to 5500? Particularly if it happens under load....

 

[gw204]

VST was my first thought.

 

[family affair]

What they said and when was the last time the low pressure fuel pumps were changed?

 

[gradywhite248]

Not sure they have ever been changed?

What they said and when was the last time the low pressure fuel pumps were changed?

 

[family affair]

I would be shocked if those pumps are still good. They have a diaphragm inside and the originals from 99 will often tear limiting fuel flow.

 

[Biscayne208]

Just had the same thing happen to one of my 250's... It was the top Low pressure fuel pump. I changed all 6 on both my motors to be safe.

 

[The_Chain]

I had similar issues if you look thru my posts...I can almost bet its your VST and the LP fuel pumps..I get my VST cleaned once a season at my local dealer...I have the same engine...I got guys waiting in line for me to part with it...anyhow other things you may consider...dirty filters from the fuel lines due to the nice ethanol gas, if you don't already get a nice racor or Yamaha 10 micron filter. There are also 4 fuel filters on this engine..one under the cowling, easy to replace...actually just bought one today..16$, but there are three more I believe that are in the VST that may need to be changed as you are asking for more fuel...even a little crud in them will give you problems...let us know how things turn out.

 

[seasick]

Looking for advise. I have a 1999 248 Grady with a XO-66 250 2 cycle. The engine runs great at low to mid power and is really in great condition. The one item is if I'm running around any where between idle and 5200 RPM is all good. Full fuel with five people on board running around 30-33 MH. If I advance the throttle to full the engine bogs down? really don't run over 51-5200 RPMs. Fuel? Air?

Did it ever run over 5200 revs?
If the vst is clogged or the low pressure pumps are bad, that motor will start to bog down way before 5200 revs. It is something else I suspect and perhaps nothing at all.
When you say it bogs down do the rpms lower, does the speed drop or is it that you can't get more revs?

 

[jbrinch88]

I agree with seasick, if it was a fuel problem your boat would most likely not even plain.