I have a Model Tech Magic with a T.T. PRO 46. I am running an APC 11-4 prop with a Mac's muffled tunes pipe using Omega 15 % nitro 2 cycle fuel. I added a head gasket to the engine and I am running a K&B non idle bar long glow plug. I have a slight hesitation in the midrange that I can't tune out and it is just enough to mess me up when trying to torque roll. I am turning 15.000 rpm with this set up. I think the problem might be the glow plug. Anybody out there have any glow plug info about this engine and pipe combo. With 2 cycle engines with stock mufflers I usually go to an O.S. 8 PLUG and it solves most problems. I wonder if this plug will stand up to a piped engine. I have played with the low end adjustment till I am blue in the face and I still can't get it right.

You could try a hotter glow plug. With 15% and an extra head shim you should be safe, 15k rpm or not.

Have you adjusted the low end needle? Throttle transition is adjusted using the low end needle. The needle is opposite your main needle and is adjusted with a small flat bladed screw driver. Run you engine up to warm it up and blow out all the left over fuel. bring it down to just above idle. Pinch the fuel line. If the rpm's pick up, she's too rich, if the rpm's go down or she quit's the low end is too lean. Turn it clockwise to lean, counter-clockwise to richen.

I have done all that. The hesitation can't be adjusted out with the low end. For normal flying the engine would be fine but for torque rolls it don't cut it. I'm pretty sure I need a hotter glow plug. Either that or a different prop. I think with an 11-4 APC it is not over propped to the point that that is causing the slight hesitation.

that motor, in helicopters, got a bad rap untill someone put another carb on one. The TT36 was the same way untill they started installing a different low-end needle. The problem was that the midrange had an extremely fat spot due to the low-end needle design being very blunt . Sounds like you have that exact problem. I had both engines, and the problem seemed to stem from the low end needle "emerging" from the spraybar right at the midrange setting where you hover. The needles were so blunt, you'd get an extremely rich "burp" right before hover point. I tapered the needle on my 46 with a file, after chucking it up in a drill,..and totally eliminated the problem. Doesn't take much, just a little taper and the transition is smoother, therefore there is not a big "bump" in the mixture at one point. The motor actually ran EXTREMELY well after that,.. sort of a daylight to dark difference.

My personal experience: Try the OS #A3 on this engine. I have found that it is the optimum plug for both the OS FX .46 and TT Pro .46.

I tried an O.S. #8 glow plug and it helped a lot but it still isn't right. I am going to modify the low end needle valve next..

Guys - I really appreciate the other perspectives expressed here. I am fighting a simuliar issue with a ST 90. I am running a Mac Long Header and mac tune pipe on my new Ecstasy. The mid range is extremely 'fat'. My transition is great, but between 1/4 - 1/2 throttle it is FAT. I've tried different tunings of the header, though you can only afford to cut 1 too many times. I've tried different glow plugs without sucess. Sometimes I can get it on the pipe in the 1/4 to 1/2 throttle on up, most of the time not. Then is boogs from trying to run it at mid range all the time. I'll check the end of the needle on mine. Filing the end of the needle makes sense (if it is blunt & I believe that it is). I think that I have an extra carb laying around. I'll check and modify that needle first and try it.
Thanks Guys!
Kevin

Try the O.S. # 8 GLOW PLUG. Whin you cut off the pieces to tune the pipe save the pieces. You can use JB WELD to glue the pieces back together carefully and the pipe header coupler will keep it all together.

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Sounds like gwright knows the trick. If you have a digicam,
maybe you can post some close-up pictures of the needle, before and after.

(My TT Pro-46 is on order)

Thanks,
Rich<>

I've got the header tuned properly. On the ST90 w/ stock muffler I tached at 10.8K rpms, with the header tuned, I'm at 12.3 (and climbing due to break-in) with an APC 15x4W prop. I cut off some more of the header and she dropped in RPM so I them slide the tune pipe back within the coupler. Believe me, I've tuned allot of headers in my time. More than I care to count.
I don't believe that it is the header nor the needle settings. That is why I was so intrigued with the shape of the low speed needle. I'll check mine tonight. If I have an extra low speed needle like I think that I do, I'll file one and try it. If it works, I post a before and after picture for everyone. "I have the technology !"
Kevin

I just remembered something about Supertigers. The two screws that adjust the angle of the nipple to the carburetor. Mark your stock setting and then play around with that. That should fix you low end. I have had a lot of experience with Supertigers years ago and moving that spray bar around will make a big difference in throttle responce. I also heard but have not tried a trick I heard of a few months ago about Supertigers. Put a piece of fuel line on the carb nipple and blow through it and have the two screws loose on the spray bar. It should be less restrictive at a certain spot and that spot is where the spray bar hole is shooting straight into the crankshaft. It is similiar to setting up your low end needle by blowing though the nipple and adjusting the lowspeed needle.

Thanks, I'll give that a try!
Kevin

and one other thing i always do first, is put a piece of fuel tubing on the needle to seal the spot between the needle and the needle housing......after assuring no air leaks, i proceed to the things mentioned above......bill w.

Kevin,
Since we are both avid funflyers, I understand where you coming from on the ST 90. I have a ST 45, I have been trying to get it set for months. I would play around w/ it when I wanted something to do. The motor would be perfect on a trainer or sport plane. Where bogging down for a second or 2 isn't that critial.

As you know we funflyers have GOT to have are throttle transition perfect are were not happy. I have been asking propnut1 for help. Finally propnut and I got together when I had to motor. He set the low end perfectly the other day in about 5mins.

He told me he buys a lot of 45's cheap because people can't get them to run right. I think he has 11-12 ST45's.

We were at a funfly about six weeks ago, he let me fly his plane. I said Propnut your throttle is perfect, what motor you running, He said ST45. I didn't believe it. But when He landed, it made a believer out of me. So right them I have been picking his brain for pointers to set up a ST carb.

I put a Mouse can muffler on my T.T. 46 PRO and now I have all the power everywhere I want it and the midrange throttle responce I need to torque roll. Problem solved. Also the muffler is quieter than the stock muffler and only weighs 2 oz.