I have had some major tuning issues with the GRP.21. I am no pro tuner so I could use some help. I have had some experience with the jammin jpx.21 &.28, os vspec & a few others with good results, but I am currently running the GRP.21 in buggy & GRP.28 in truggy (JAMMIN X1X CR & X2 TRUGGY) The GRP.28 tuned very easily but the .21 has been frustrating. The problem I have is that it seems like it is always running very fat off the bottom until it hits the mid. My current needle settings are aprox. 3 3/4 on HSN and 5 on LSN. If I lean out the top much more it continues to flame out. If I fatten the hsn back and lean out the lsn then it sounds lean and has little bottom end. I have tried to keep temps arround 190 -205. I run a fioroni turbo slider clutch, 13 tooth cb and a jammin jp3 or jp4 pipe(most the time the jp4 as it seems to help the bottom a little more. I have tried the c6 ,c5 ,c4 GRP plugs. I run BYRONS GEN2 30% and have tried running it with 1 extra shim and also stock shim set up. I have researched this thread and a lot of guys are running totally different needle settings. some say 3 1/2 hsn & 5 1/2 LSN & some are 6 hsn & 2 1/2 lsn. 2 1/2 lsn just seems way to lean and 6 to fat to even fire. Although when I called horizon hobbies for stock settings they gave me 6hsn & 2 1/2 lsn. HAVING 1 HECK OF A TIME WITH THIS ENGINE any thoughts or input would be appreciated. THANKS