When you  use motors for the first time, you should also make sure you have the motor properly broken in.  This will range from six tanks of fuel for one engine to almost two gallons for others.  OS, for example, says two hours running time for their motors. A good break-in procedure is to use the same fuel as you will for your Stunt run ,and try to do your break-in on a bench; this is a lot better and an easier way to do a proper break-in. Use  A diameter, one inch smaller than you plan to run at, at a 3 or 4 pitch, should be the prop to use.  This will let the motor turn many revolutions more per motor run time.  Start out in a very sloppy four-cycle for cast iron lapped piston and  most ringed motors, slowly progressing to the fastest it will run in a four-cycle, then put it in a short two-cycle burst for short times (about 10 seconds each).  After the correct amount of time it should be able to run in a two-cycle without heating up and going leaner. Using  3 to 6 ounces per run with 5 to 10 minutes  cool down time in between.


Hi
The excerpt from the fuel article is above, the entire article is pinned at the top of this forum, you may want to read all of it.
Your 51s are tight so just go slowly before you put much 2 cycle time on them

Regards
Randy

I believe the exception to the long break-in rule for the ST51 would be one reworked by Tom Lay.

My T&L ST51 got exactly 10 minutes bench running at slightly rich needle setting.  Into a plane it went, and it put out full power from then on.

Floyd

Hi Randy,

      Actually they are the ones you did for my brother.  He has been so sick that he can't do much.   So I asked the question for him.

Thanks

Thanks,
 
That's what we'll do.