Ive got a new hellfire. it starts and idols fine but when i apply throttle it doesnt have any power. The car will move slowly but only at walkng pace, even if i apply 1/2 throttle orittlemore. It accelerates when the truck is off the ground on the stand but also doesnt reach any peak power output. when i put it on the ground it has little. I have changed nothing on the ca r so it still has factory settings.. Could Nitro content in the fuel cause the power problem? cause the fuel im using is about 5% under the recommended

It may be running too rich.. Also, check the clutch shoes.

Have you followed the break in procedure for the engine? Sounds to me like it is still set rich from factory(pre break in settings). You must adjust carburetor properly after motor is ready to run higher rpm's.

I had the same exact problem when I was breaking mine in. I just leaned it out about 2 and a half turns and it runs like a champ now.