300x won't rev up

[Wild Bill]

Did some work over the winter, first time out it ran great. Then it started slowing down first trip 98 second trip 94 third 84 fourth 71. Starts fine idles fine planes and runs fine just wont wind out. Checked compression, leak down, reeds, fuel pressure all ok. tried a different map sensor, new champion plugs still wont run right. Any suggestions?

[tux974]

Make sure you are running Champion QL77PP plugs! Sounds like what NGK's do, they go away.

[Wild Bill]

That's the plugs that are in it. Update, went out today and before the thunderstorm ran us off I noticed at 5300 the tack started jumping a little like hitting the limiter. Then it cut be down lower and I could hear it stuttering, then back to 5000.
I think I inadvertently set it back in break in mode. How long does that last? I heard turning the key on and off 3 times in short succession will do that, am I correct? I did it playing with a fuel pressure regulator.

[vnemous]

If you move the shifter in and out of gear five times it will go into break in. Don't know about key doing it.

[fortlaudypower]

what fuel lines are you using? I ask due to the same thing happening to me, liner from the older fuel lines blocked it.

[msg11]

The shop manual says the period of time is 2 hours.

[vnemous]

Yes break in is two hours. Engine will only deliver 75% during this time.

[Wild Bill]

Thanks for the help, I found it, something simple. The weather pack plug on the water pressure sending unit worked loose. Pluged it in and ty wraped it and viola full rpm. Maybe that wasn't it but it works now.