2000 225 HP OX66 RPM's

[kt]

I have a 2000 225 HP OX66 that I can now only get 4700 RPMS out of. It has a Yamaha 27M prop. It still runs strong and no problems of any kind other than the RPM drop. Any Ideas? At 4700 it still runs 62 GPS MPH with two in it and one tank of gas.

[kensafishin]

Sure your rpm gauge is accurate? Notice when you turn your key to the first position before starting does it drop to zero and when started goes to the correct idle 700-800 rpms.Also may be 02 sensor but mine would not go over 5500rpms then drop to 4800 while running.

[kt]

Digital Tach. 0 when key is in on postion. 700 while at idle. 02 sensor replaced in Jan 07.

[kensafishin]

How old is cranking battery?

[kt]

1 year. 850 CCA.

[kensafishin]

Fuel pumps mmmaaybeeee. Hamfisted or 21XDC should be able to help on this one.

There have been posts on this before and bad batteries can cause this,not an expert but have seen it on other boats also.

[Beetle]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kensafishin &raquo;</TD></TR><TR><TD CLASS="quote">Fuel pumps mmmaaybeeee. </TD></TR></TABLE> That would be my guess. The Three fuel pump diaphrams being cracked could cause this. It happened to my 2000 200 OX66. The o2 sensor would be my next guess. Get it fixed befor you blow it. Talking from experience!

[kensafishin]

I just replaced my fuel pumps after 7 years.Was told that they should be done every 3 years.It wasnt doing what yours was but could smell gas when at the ramp and sputtered when getting on plane.If you havent changed them I would.You can look up at one of the first posts listed on the Yam boards on how to do it(Ox66 fuel pump diaphrams).I got them from boats.net.

[EL Skeeter]

Try tapping on the gauge. Every so often mine sticks at WOT.Shows 4700 RPMs I know better, should read 55-5700.

[kt]

Took it to the shop today. They could not find a problem with anything. Had them install new plugs. Will take it out tomorrow and give it a try. May I need a new prop any suggestions on which one?

Thanks for all the replies.

[21XDC]

I'd run a 25T1 and make sure you have the BR8hs10's ... They run longer/better than the BR9hs10's

Let us know what happened.... Sounds like you had a fouled plug to me.

[cottonmouth]

I dont think it is the prop.I run a 27m on my yam. 225 efi and I can get to 6000rpms. My prop has been worked on by Rich Boger.I dont know how big a difference that would be though.Good Luck and let us know what you find out.

[kt]

Thanks for all the information. Took it to Fritts OUtdoors and they could find nothing wrong. I had them install new plugs. I am going to try a Yamaha 25-T1 off of my buddies 520 this weekend. Will post results.

[Larry]

kt when my 2005 ZX225 was new I had the same problem they changed out the 02 sensor and the fuel pumps then I went to a 27T and started raising my mtr. I raised it until I was getting 6000 RMP's and I was running 74 MPH GPS. Just watch your water pressure. 12 #'s or higher is ok. Hope this helps.