I had exactly the same problems with my GRP .21 Tuned. After reading some other forums someone suggested to try a different carburetor which helped him to stop the tuning problems. I used one from my RB S7 and the problems are gone. The engine is running great now en holds it's tune.

Thanks for the replies. I will take the motor back to the original settings and retune.

Make sure you don't let the lid slap shut. That will cause the car to go rich after a fuel stop.

why is that?

Yeah, I can see a very quick pressure increase when the lid closes but it should equalize very quickly.

Check the needles on your carb very closely. On my GRP, the o-rings for the low and high speed needles were shot, and the needles were backing out due to engine vibration when the engine was running (causing the motor to run richer and richer). Drove me nuts, till I replaced the o-rings.

I just got to thinking about the mixture changing when refueling problem. Could the fuel temperature have something to do with it? When you are running the exhaust going into the tank could heat up the fuel. When you refill it with cool fuel could it make it run richer? Just thinking out of the box here.

Try lengthening the pressure hose. When the fuel gets lower in the tank I looses pressure. Then when you refill, the pressure comes back up making it force more fuel in. Just a thought.

That is an idea. I had a helicopter that had that problem. You would have to start out rich to keep it from leaning out too much.

question i have the 086 pipe and 6 mm restrictor in and my track is on the medium to small side there are some guys running tourque pipes on the buggy and get better run up to some of the jumps i keep up just fine but feel the bottom is a little soft for these conditions. if i switch to the 053 will it have more bottom end like the tourque pipe or should i just go with the 007

the 053 is the one you will want to run

What is the manufacture of these pipes?

Dynamite.

I was having a torque issue with a tuned .21 in my truggy with a dyn 053 pipe. mid was great and top end was not bad, but the low end suffered a little bit. I installed a long RB header and what a difference. I used a long header when I used to run the stock GRP 2053 pipe and that seemed to help it too. The long header and a 053 pipe work great for me in a truggy.

Who makes the long header? What part number? What about the Ofna pipes?