I switched from 20% nitro to 33% nitro about 2 tanks ago and everything seemed fine. I ran the truck to today and even when set really rich the engine kept over heating to the point of smoking. It was 70 degrees outside. I did not have my temp gun with me but she was very hot. I have never had a problem with the engine getting hot. I reset the high speed needle back to factory default and still had the problem. The engine was also reving up and down at idle and stalling a lot even when it was not hot. Is the problem because I switched fuel or could it be something else? Like I said I have only ran 2 tanks of 33% through the engine so if it's the fuel should I switch back. Thank you for any help you can give me.

Try changing the glow plug.

also did you add a shim to the head when you switched? could be part of the prob, and if you havent all ready cut a hole in the body to increase air flow over the engine

erratic idle means needle imbalance..i had that too..i said hmm..i wander if i richen the low speed will it stop..sure enough..it stopped

acording to my lhs (they're pretty cluey by the way, they'v been running for 36 years) recans more nitro increases the running temp, the guys in there suggest just running 20% in cars and trucks

also could be a layer or 2 of dirt on the out side of the engine

i had that prob then i cleaned the inside/outside of the engine
and walaa
brand spankin new
lol

Check for a crack in the carb, inside right where the slide valve goes through...the side where the blue boot is. I've seen 3 out of 3 have it when that problem starts. After my second carb body, I just ran the low speed half turn out from factory and it cancelled out the extra air getting by the crack...I know it's a ghetto fix but I don't want to shell out the $85 for an OS carb yet.

Try a new plug first, if that dont work, richin the low speed a hair, if that dont work look for a air leak. Traxxas motors are selaed pretty good , but look at all the o-rings. If you take out the carb all the o-rings on it will have to be replaced, that are on the carb neck.

YUP!! check the carb. It's definitely some kind of air leak. I usually start with checking the fuel tubing since it's the cheapest and most likely to get a pin hole. After that inspect the carb.

FYI:
Your 3.3 engine will handle 30% nitro with no problems. no need to shim the head. Also running 30% will lower combustion temperatures. It's the burning of the oil that helps create temperature along with the friction.