I got a Pro .61 a little over a year ago to put in my VMar Spit. (Yeah, I know, VMar=crap.)
The plane has been sitting on the bench for quite some time now and I figured I'd better get that engine running!
I got the engine used-ran once-here on RCU.
I mounted the engine on my test stand and removed the cone shaped baffle from the muffler. Put on an 11x6 APC and filled my test stand tank with Wildcat 10% Premium Xtra, (18% oil, 80/20 castor/syn mix). There was an old used Fox plug in the engine so I just left it in there for break-in.

First 10 oz. tank: held 13,980 RPM consistently. Peaked at 14,100 RPM. Idle: ~2300 RPM. Mid-range was rich. Low-end was... I guessed rich.
Second & third tanks: Same as first but got a slightly higher peak. Around 14,150 RPM.
During the fourth and fifth tanks I started richening the low-end. Wrong. Mid-range got worse. Started leaning the low-end and got it to idle around 1800 RPM. Mid-range still slightly rich but MUCH better. Peak was now holding nicely at 14,040. One more click leaner and it would hover around 14,100 RPM. Yet another click leaner and it would vary between 14,040 and 14,200 RPM.

The stock muffler was without an O-ring where the rear cone meets the chamber so it weeped a good bit of oil.
The front bearing-as Dave Gierke mentioned in the .61 Shootout-leaked a small amount of fuel/oil during operation but it didn't seem to affect anything. I still have that old Fox plug in it. Tons of compression and all seems well. When sunlight permits I'll probably lean the low-end a little more to try and smooth it out even more.

All-in-all I'm rather impressed and slightly deaf now. Hearing protection is ABSOLUTELY required when you remove baffles!

It'll be interesting to see if my homemade Pitts muffler can hold up to this kind of punishment.

I have the TT61 Pro on a Global Right Flyer 60 with an APC 13x4W. I started with an APC 11x7 and it was just too fast for a beginner and even my instructor commented we should slow it down some. We get a really good slow idle, but several times, he had to kill the engine to get it to land.

My muffler still has the baffle and I'm using Magnum 10% fuel.

If I remember correctly, these are my tach readings:
11x7 = about 12800 peak rpm
13x4W = 13100 peak rpm

I really like the 13x4W. It does require a higher throttle setting for cruising, but the instant acceleration makes up for the increased fuel consumption; and it really slows down for landing.

Now I just have to learn to land the thing by myself.

Thanks for posting your tach. readings.
I'll be propping mine down a good deal to maximise the engines torque.

Up and flyin' huh?! Good!
The hardest part of landing for me was judging distance and airplane speed. Sometimes I came up short and stalled. Other times I came in too fast and over-shot the landing area.
With a little practice you'll get better at judging speed by how your plane reacts to inputs.
Distance is a little different. Before taking off place your plane in the place where you'd like to land and walk back to the pits. Take a good look at how big/small your plane looks where it's sitting. When you come in for a landing you'll know your where you want to be when your plane looks the same size when it was just sitting there. Taking note of background objects also helps.

Good Luck,
Jeff

More tach readings

15% nitro, 18% oil. Different muffler.
I made an inverted muffler out of alluminum, 4-40 rod and nuts, and JBWeld. A brass pressure nipple and some SS screen door screen for sound reduction and added back pressure are also included.

MAS 12x8: 13,000 RPM
TF 14x6 PP: ~10,000 RPM (Too much prop-engine ran hot and wouldn't hold a consistant peak RPM)

My tack readings are as follows, keep in mind I have a tuned pipe I picked up second hand so I,m unsure of the brand?

Fuel used is my own mix of 10% nitro, 10% cool power synthetic oil, 10% caster oil and 70 % methanol.

11x8 APC- 13000 rpm
10x8 APC- 15500 rpm

These are the only props I've Tacked. I've used 12x7 and 13x6, the 13x6 seemed to unload too much in the air with the prop going supersonic. The 12x7 was very good however took a few secs to come on pipe.

The 10x8 was still on pipe at half throttle in the air and really got my World Models 46 size Miss America moving. The 11x8 was great too though the vertical was not quite as awesome as the 10x8 however the level speed was very similar to the 10x8 just without the rpm.

When I get more readings I'll post them.

Adrian.

Adrian,
I just came back to see what my RPM readings were and saw your post.
It seems a little odd that I was getting 13K with a 12x8 MAS and homemade inverted muffler while you were getting the same 13K with an 11X8 APC and TUNED PIPE.
The 10x8 sure does spin though!

One of these days I'll try the 13x7 APC I've got in the basement.

when i was down at perry this year,i picked up an older GP sporster .90. 70+ span,built probably 20 or more years ago,it was built and covered with fabric and dope,then painted. this mobile lumber pile weighs in at almost 12 pounds RTF.anyway,the reason i bought it was because it was full of good ballbearing servos,fuel tank,everything but rx,and engine. not a bad buy for $40 bucks! so,the guy said he flew it with an old wore-out o.s.61 2-stroke. well,when i got it home,i didn't want to have to do a bunch to it to put an engine on it,since it had hardwood rails to mount motor,so i put a NIB TT.61 pro/12x6 MAS prop on it.never been run,unwrapped it from tissue and bolted it up. everybody that saw the plane/engine combo,said it would never pack the plane,a crash waiting to happen. well! to everyones suprise,it took off in about 20 feet,and climbed out at about a 60 degree angle!!! and in the air it is fast! got a friend there with a CG tiger2,with a ST .51 on it,and i can out run him!!!easy!! and to boot, the engine has about 4-5 tanks through it,and we have yet to touch the needles,it was that close out of the box! i love this engine,a real powerhouse,and cheap!

I know this post is old...

Tried the APC 13X7 on the engine yesterday. Used a plug of unknown type. Might be a Thunderbolt.

I tached it at 10500 RPM with my pitts muffler and ~10% fuel (the fuel is old so I don't really know for sure).

Whew man! That thing runs like a raped ape!

Just picked up one and hope to ligt it up this weekend on the test stand. I picked up a few props too to compare figures. I'll post the numbers as soon as possible. I plan on using the following props: 11x6, 11x7, 12x5 and 12x6. I already removed the baffle from the muffler. I compared the muffler to the one to my .61fx and the TT looks to be a bit larger (move volume). My .61 fx is fairly new so I might run them both and do a "TT vs OS .61 shoot out"

I tached my TT61GP today at the field.

Turning an 11x7 Master Airscrew and with a tuned pipe I'm getting 13,450 RPMs with 5% nitro in the fuel -- which I'm more than happy with.

Not bad for an $85 plain-bearing engine running on 5% fuel.

This engine has had about 8-10 gals through it and it's got so much pinch that my electric starter won't even turn it over when the temperature drops below about 55 deg F (the same starter has no trouble with my Saito 100 so it's not "wimpy" by any means.