I've just purchased a thunder tiger pro .61 to power my 60 size Extra. I've put 4-5 12oz tanks through it and it still runs HORRIBLE!! I can't seem to tune this thing at all. First off, it starts fine, runs and transitions well when it's cold. It is mounted under a cowl, but has ran this way with and without the cowl. The motor is mounted on it's side with a Slimline pitts muffler, which I've tried restricting and that didn't help. I'm running a 11X6 prop for break-in and a fox glow plug with idler bar. I'm also running 5% fuel which I've never had a problem with any other engine. Most of my experience has been with OS and have had nothing but good luck. The only reason I went with the Thunder Tiger was for information purposes. I help at a hobby shop and we just started carrying TT and I wanted to know first hand what they were all about. So far...not impressed!

Ok...the symptoms. High RPM's are great. If I run it at full throttle for anything longer than 30 seconds or so then drop it down to idle, it will die. The transition from idle to half or full throttle seems like it's rich. But, if I lean the bottom, the motor will not start. I've played with both needles but without success. I've checked for leaks, and such. It's got brand new fuel lines, new sullivan tank, etc. I'm wondering if 5% is not enough or if I need a different glow plug? The other issue is on the ground, the high needle setting seems great. When held up the engine does not lean out. But, once in the air the motor seem rich. Not getting full RPM at all. This was also on the 3rd tank or so and that might just be break-in. My major concerns are with the transition issue and the fact the motor won't idle once dropped from full or 3/4 throttle. It'll slowly drop RPM until it dies. Any help would be greatly appreciated!! Thanks a bunch!!

Dave

These engines aren't known as power-houses but, an 11x6 is on the small side for a .61.
My TT.46 turns one at 13,5. I wouldn't expect too many more revs in the air than on the ground at WO with that prop. It has to be screaming near 16K!
The Fox plug is the other problem. The manual warns against them and none have worked in any of my many TT and low nitro fuel will just make flame-outs worse.
You may have better luck with a 12x6 and an OS A3, #8 or K&B 1L.

Kirk

A few things to check and or change. Get rid of the Fox plug and install an OS 8 or a Sig GP-002 plug. Next check all the engine screws especially the rear cover ones. Next you mentioned that there were no leaks at the "O" ring under the carb that you installed. Did you maintain some downward pressure as you tightened the draw bar? Does the fuel you are using contain at least 18% oil of which at least some is castor oil especially during break in. Does your pitts style muffler have the pressure fitting in the correct place to provide correct pressure?
If it were my engine I would, at this point, put on the stock muffler and mount it to a stand to get it dialed in and broken in. If it wont run properly that way, it should go back for replacement or repair. You are introducing too many variables all at once with the cowl and with the non stock muffler and a new engine that hasn't been broken in or dialed in. If it runs fine on the stand the problems are with the exhaust and lack of cooling with the cowl.

The Guys are right---get rid of the fox plug---I use an O.S. #8---also the Pro. 61 carb uses a spray-bar that has a fuel-atomizing slit along one side, make sure it's pointing downstream---it can be rotated 360 degrees

Fox plugs are OK, but not the idle bar plug. Fox Gold Post should work fine. But since Tower doesn't carry them not many shops do. I like the Enya #3 when having problems. You need a hotter plug when using 5% nitro, which an Enya #3 is. The OS #8 is fine if using 10% or 15% nitro. I think the combination of low nitro and a fairly cold plug is your problem.

One more thought. Could you have gotten a bad batch of fuel?

My Thunder Tiger Pro .61 did the same thing today at the field. I was trying to get it to idle reliably for the maiden flight of my 4*60. I'm running 15% nitro and had a McCoy idle bar type glow plug. What you described to a tee: It would Idle for about 8 seconds and then die. It acted like the low needle was too rich, but whenever I'd lean it a tiny bit, it wouldn't start! My instructor and I kept playing with it until we finally got running OK, but not good by any means. I don't see anything obvious with the fuel system at this point. The tank seems to be holding pressure fine.