250XS help needed

[LarryP]

ON a blistering hot day (100 degrees) with high humidity how much speed will be lost? I fished a T on Sat. and the boat had dropped 10mph in speed. Couod not find anything wrong but what is weird is I only ran about 25 miles and it used 3/4 of a tank of fuel .

Don you got any ideas? It is an 04 racing motor. THanks

[EuropeanAM]

It's not uncommon to see 100-150 RPM loss on a really hot, humid day. 10MPH seems VERY excessive.....

Start with the basics- compression, spark test, and fuel delivery/pressure/air pressure.

You may be down a cylinder.... or may have a spark plug that is fouled (or cracked).

Also.... check for the little yellow "plastic plug" in the center of the flywheel. If it's not there.... look down through the throttle plates (must remove black plastic cover first), and ensure it's not sitting down inside the intake. You should see nothing down there but "some oil".

[LarryP]

Checked everything and found nothing wrong. Plugs had a little soot on them. Changed out the TPI and just ran the boat to 84.9.

[Largemouthlou]

So the TPI was the problem Larry??

[2500]

that was it! how'd you know it was it (Just asking to learn) since you said all else was good, how'd you go to TPI?

[EuropeanAM]

I'm also curious how you jumped to the TPS.... did you have a DDT or Computer Diagnostic check indicating faults (as a hint)?

[LarryP]

We are still not sure what it was. Everything showed normal on DDT and leakdown test was ok. All cylinders were firing on the DDT. My mechanic had a spare TPS sitting around so we tried it. There literally was nothing showing wrong except the top driver side cylinder plug had more than mornal soot on it.
Got no idea but I will know Sat since I have a T.

DOn,
What exactly is the TPS?

[EuropeanAM]

Throttle Position Sensor (also formerly known as TPI, or Throttle Position Indicator).

[2500]

hope thats it but in the ever ending "making um better" its another place to look wish they could have gotten pics of the sooted area so we all can look