I dont know about the ST, but I use that prop on my FP .40,, I would guess that you may need a larger prop? however, I am NOT an expert, just my two cents worth

Been playing with a Frank Bowman ST V51(not G) on a Brodak Arf p-40.  I'm using Powermaster 10% 22% 50/50 and thunderbolt plug.  I ran it on the bench for about 20-30 minutes for 3-4 minute intervals and have flown the setup now about a dozen times.  I know the thing could use more break in time but I have to say it is acting a bit strange.  Sometimes it will lean out and runaway during the flight, other times it will get stuck in a low power 4 stroke.  I have tried different tanks I am running a APC 11.5x4 right now as it didn't seem to want to pull anything bigger.

I did try taking off the tongue muffler today and seemed to get a better run.  Is it overheating and running away?  Do I need to add head gaskets?

Thanks to all,
Bruce   

Hard to tell, but with 10% nitro, it could be experiencing some "overcompression".  The engine guys tell me that more notro works in a way very similar to raising the compression.  Might try 5% if you have any..  I always use a 12" on my G51, and many guys were using 12" on the .46.

Bob Lampione left a Big Jim reworked "V" 51 here and it has his "signature" hemio head.

Been playing with a Frank Bowman ST V51(not G) on a Brodak Arf p-40.  I'm using Powermaster 10% 22% 50/50 and thunderbolt plug.  I ran it on the bench for about 20-30 minutes for 3-4 minute intervals and have flown the setup now about a dozen times.  I know the thing could use more break in time but I have to say it is acting a bit strange.  Sometimes it will lean out and runaway during the flight, other times it will get stuck in a low power 4 stroke.  I have tried different tanks I am running a APC 11.5x4 right now as it didn't seem to want to pull anything bigger.

I did try taking off the tongue muffler today and seemed to get a better run.  Is it overheating and running away?  Do I need to add head gaskets?

Thanks to all,
Bruce   

HI Bruce

The ST 51  likes to have some pitch when it runs, they run very well on  a  Bolly 12.5 x 5.5  , Bolly 12 x 6, Bolly 12 x 6.5n 3 blade , BYO  12 x 5, New Zinger 12 x 5, Old zinger 12 x 6, and  several other props of the same range, I have found the prop you are  using on it to be  good for a  Thunder Tiger 36.
You need to "load" an engine  for a  good  2-4  break, too Small a prop  or  no load  and  it  will just run around in a  "dumb" run  without  cycling
Try more prop and more pitch, and you should not need  10% until the summer heat gets here, I would start with 5%.
By the way  many have used this motor  with a  11 x 7  4 blade too.  I have setup hundreds of the ST engines  and  I think you will find  this helps.  I ran the same Motor on a  Magnum  with 5% nitro  12 x 6.5 n  3 blade and it flew all 4 with just nice 2 cycle beeps across the tops of the maneuvers

Regards
Randy

I started with a 12" prop and the motor tended to run very hot and sag, therefore I figured gee, this engine is not broke in yet or the compression is too high maybe or too much nitro in my fuel for the ambient temps.  So I fit a smaller prop.  The smaller prop did let it run without overheating.  I installed the only 12" prop I had, a MA 12x6, I removed the tongue muff and it was able to run a bit cooler and seems to run a bit better and with more power.  I'm thinking it just needs more time.

bruce

I started with a 12" prop and the motor tended to run very hot and sag, therefore I figured gee, this engine is not broke in yet or the compression is too high maybe or too much nitro in my fuel for the ambient temps.  So I fit a smaller prop.  The smaller prop did let it run without overheating.  I installed the only 12" prop I had, a MA 12x6, I removed the tongue muff and it was able to run a bit cooler and seems to run a bit better and with more power.  I'm thinking it just needs more time.

bruce

Hello Bruce

With a very OLD  V  ST 51   I cannot believe you have a  too high cpmpression problem, these were not high compression engines to start with, Do you have  1 ring or 2?  It sounds like  you maybe need more breakin time, or you need to  up the  pitch and  nitro so you can run the engine richer...thus cooler
let us know  how  it works for you

Randy

It is a 2-ring motor.  Frank Bowman rebuild.  Hope this helps.

Bruce

HI Bruce

Yes that will make a  BIG differance, the 2 ring motors  do NOT like to ryn hard or be pushed hard, they are a lot happier on higher nitro high prop pitch and richer  runs. The dual ring has much more drag, and thus friction, so It will heat up faster than teh single ring, and if the ring gaps are really tight  this will need a lot of breakin.
I also assmume  this is a  chromed sleeve motor, most of them were.  Keep putting more  time on the engine and  try the other  suggestions,  I think you will  have  a good  engine  soon

Regards
Randy