You may want to get rid of the pull start all together. If you are running the NX-26 engine I have an extra NX-26 ROTO BACKPLATE and roto starter I would sell cheap. I know what a pain those pull starts can be. I went through the same problems with pull starts.
ALSO, if you are messing with alkaline batteries you are not getting the most out of your Matrix and you are risking a runaway. Grab a 5 cell receiver pack and you will be so happy you did! It will allow the servos to operate quicker as the receiver packs have more voltage and last much longer...
If you are interested pm me.
Good luck