I have two fox 35's with the blocking stick in the bypass.

The first one works better than ever with no fox burp.  I did 8 figure 8's in a row with no burp and I did some outside loops, no burp.  However, when starting it, it gets very tight.  It takes a lot of pressure to free it up.  Then when it starts, it is marvelous.  Smith NVA, hot glow plug.

Case number 2,  has the mod but will just not run right.  It doesn't run up to speed - just sort of goes slow - no umph - not enough power to to a loop on a light Trixie.   Hot glow plug, Fox NVA. 

Any thoughts on either one, what to look at.

Thanks ahead of time.

Hi
Another thing you want to check is that the plug your using in the bypass is not too large, if all else is good, trim it down smaller

Randy

The newest Fox 35's seem to have pretty good quality control, but the older ones can be uneven.  I had one that simply couldn't run a 2 cycle, even after extensive break in.  Start the motor up blubbery rich and start leaning out.  It would lean out to a fast 4 cycle, then gradually change to a slightly slower 4 cycle, and then quit lean.  Made the plane unflyable.  It had to be set so rich it couldn't really get into the air without a lot of whipping.  Then it would lean out and quit.

Never did figure out what was wrong with it.  Could have been too tight a shaft fit.  That can take year to wear in. 

If you still have the box, send it back to Fox for repair.  They usually replace bad motors, sometime for a nominal fee if it looks like you mucked around with it.