It could be motor bearing, and then again, it could be any bearing in the buggy or truggy hour running. Check clutch bearing, springs, shoes, wheel bearings, diff bearings, universals. That's just a start. If you have a temp gun, you check each wheel bearing after you ran it on the track, if its a wheel bearing, there will be a significant difference from one wheel to another's if a wheel bearing is bad. This is just a start.

Couple things to start with if the drive train is free as posted earlier:
1.) Have you checked your temp gun against other temp guns? if yours is ready 20* higher then a some other racers, I would say your Btt is perfect. 270* to 280* is fine with the low cooling heads. My Btt is on its 8th gallon, I just got it pinched and a new rod after the 7th gallon and I have been running in the 270* to 280* range since it dropped its nuts. I would say 250* is about max on the P5, but I haven't tuned a regular cooling head engine in a long time... someone else can add some input there.
2.)How is your idle? Also you could be lean on the LSN and if your track has a lot of slow corners, short straights, etc. you are using the LSN more then you think and then it is getting plenty of fuel when you reach WOT showing a lot of smoke at that point.
3.)Also how much time is on the engines? If they are starting to loose compression and begin flaming out you could be getting blow by causing the explosion to go down the sides of the P/S creating more heat.

Well I don't really know how accurate my temp gun is compared to like an exergen. But the idle is good. Sits and purrs like a kitten. The btt has less then a gallon on it and the p5 has about 3 gallons on it. What temp gun would you guys recommend? I don't know if I want to spend the coin on an exergen if theres a cheaper one out there thats just as accurate, but if that's what I gotta do then Ill do it.

Does anyone know an acceptable tolerance for a plus 4 tuned crank pin? Picked up a used plus 4 engine and I had a spare crank for it laying around and was wondering was it any good to keep for a back up...

the under head oring is in bad shape on my p5xlt is this something i have to have or not i have heard different opinions on this

No worries...you don't need the oring at all. It simply helps keep the head button clean and has no bearing on performance.

You can order the just the orings if you want to keep using them.

thank you ill put my motor back together

I was running my new keep off 21/4 with the 2096/41021 combo and the power was very smooth. The header was a loaner and I no longer have it. I'm going to get a new one. In the mean time, I have a werks 2058 pipe and header I could run and I also have a picco header that came with the 2099 pipe. Would that header work with the 2096? Its seems its a little shorter. How about the werks 2058, will I lose the linear powerband and some runtime from the 2096/41021 combo? thanks guys

4.91 and under I would consider worn out measuring on the very edge of the pin. That's where the most wear occurs.

Ask around and see if you can get someone to temp it with theirs and compare with yours. The btt is not broken in yet under normal conditions at 1 gallon, they are normally really free and ready to hit higher temps around 2 gallons. As far as makes I use a ray tech gun, but I only use it as a reference

2058 is great, give it a shot.

Hey guys just wondering the best plug to run in a Novarossi S21P5XLT .21 5Port?
Also Wat average run time can I expect out of this engine on a tank, Wat is a good midrange pipe to suit it,and how many litres should I put through for break in before I go to race tune.
Any help and advice would be great thanks

Thanks for the info. Its at about 4.91/4.92 so I'll probably get another gal or so out of it you think?

Ya possibly, but you risk throwing a rod. If you put a new rod on it you could get even more life out of it.

Rcmoe,
look up Jenny's RC on Ebay. I think the screen name is *JRC* They part out Btt's and you could probably get a crank for about half price. I got a block with both front and rear bearings and the red gasket for $54 shipped after I sanpped a screw in the backplate of my old block. At 4.92mm you should start looking for a new crank sooner then later.