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ST2300 Testing and Experimenting

Old 01-09-2011, 10:06 AM
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min$2crash
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Default RE: ST2300 Testing and Experimenting

Ummm, I've been reading thru a lot of this thread to learn about ST deadsticking issues for my 3250, and while I have a few new directions besides new carb (THANKS, ALL YOU POSTERS!), I am struck by one overwhelming concern...
There was a bright Red X on day one of this thread when the OP said one prop ran better than the other.
What about prop balance? I don't ever remember reading that this was pursued. Prop imbalance can drive fuel foaming, which makes needling impossible.

That's going to be my next focus. I forgot to balance mine ..... and it turned out to be pretty far out when I finally checked it. Lots of sanding, and double doping the opposite side finally did it.

Meanwhile, I have drilled out the tiny ST carb inlet nipple a tad, pulled the needle and stoned some rust off of it (OOH, never seen that one!), and used red silicone (Permatex hi heat from auto store) under the brass spraybar because I have seen this as a big variable air source on this carb in my 51's. If and only if you are good with a fine stone: the back/sealing side of this brass piece tends to have some burrs that keep it from sealing flush on the back face.
The red goo is easier for non-machiinists.... but you could remove those burrs to improve sealing and then still be able to adjust (rotate) the spraybar for midrange in-the-field, so to speak. Either or, really... so I did both!
(I can always peel off the silicone at the airfield).

So that's where I am, one question:
I am mounted sideways, cyl head at 9:00 from the front. My carb needle points down, though. That is contrary to the manual (180° out). Any data out there that this is a problem?
I prefer it this way because it leaves the idle needle up, where I can get at it, and keeps the fuel line low, where it comes thru the firewall. Besides, the thr-servo pushrod routing is a real "beach" when you use that big backplate!
Old 04-22-2011, 05:02 PM
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Default RE: ST2300 Testing and Experimenting

Just wondering how you came out with the big Supertiger? Best Regards Capt,n
Old 04-22-2011, 09:29 PM
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Default RE: ST2300 Testing and Experimenting

Hi!
If you have the engine cylinder at 90 degrees and the carb high speed needle pointing down...you have the carb mounted the wrong way!
It doesn't matter really ,but why have it in that arkward position!???
Turn the carb around 180degrees and you'll have the high speed needle pointing up and the R/C throttle arm pointing down, the way it should be.
Old 04-29-2011, 08:18 PM
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Default RE: ST2300 Testing and Experimenting

Actually, its not awkward at all, as I can reach under the engine and adjust the HS needle easily. This leaves the Low Speed needle on top where I can get at it easily with a screwdriver.
Once things are set and the cowl is on, I will put an extension on the main needle for daily tuning of the HS needle. Low speed needle will not be adjusted at that point. Access hole for the HS needle extension will be on the bottom, out of view. This is how I planned it, actually- for the longer term. But alas I have not flown with the cowl on yet because the engine still goes deadstick at 1/2 tank despite hours of tuning with loads of expert help.

I even tried the hotter Enya #3 plug that has helped all of my supertiger 51's to no avail.
As for how it went,capnjohn, all of the above 5 "upgrades" plus a bubbleless clunk did not solve the deadstick at half tank issue, so I set up a cheap manometer with a few feet of fuel line hooked up to the muffler's pressure tap.
I believe that I got that idea somewhere in this huge thread. If the fuel were water, 12" of water would indicate ~0.5 psi. This stuff is lighter than water (SG~0.7) so I expect a proportionately higher 17" column for 0.5 psi.
Actually, numbers aside, it makes perfect sense that the tank backpressure should raise a column of fuel ~= to the nose-up fuel draw distance if the carb has no fuel suction to speak of.
There is no significant backpressure(<0.5" in the Utube manometer= <0.1 psi), even with one exhaust outlet plugged on the JTEC pitts muffler, so I think that I will need a pump or 7C carb.
With that muffler outlet restriction, the peak RPM dropped by ~1000 so I opened it back up after the test as that seemed too restrictive.
This surprised me, as the stock ST cylindrical muffler's outlet does not look any bigger than my 3/8" dia single outlet pitts.
To prove the point that its a lean-out , I just richened up the main needle to maybe 4 clicks leaner than 4 stroking, and managed to fly a full tank or two out barbling to beat the band, and hovering to lean it back out occasionally.
Able to fly it dry and the compression felt much better after those two rich tanks. My conclusion is that needling for peak on a full tank then two clicks richer results in a lean-out at half tank because the carb has no significant suction and there is no significant backpressure so its metering is very sensitive to tank level.
Meanwhile, I am really enjoying my 1/3 scale Byron Pitts- every one of its 11 landings has been a dead stick, but its still a blast to fly- biggest plane I've ever flown and I am starting to understand the "bigger flies better" adage..
That's how it went, thanks for asking capn!!
I plan to get a Perry pump and use the manometer to set for 0.5 psi pump pressure before needling around much. Sound like a good plan to you?
This is my first pump, and I have heard a lot of stories of bad experience with a pump. The pump will also allow me to add a hopper tank per your sketch at the top of this page.
Old 04-30-2011, 12:09 PM
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Default RE: ST2300 Testing and Experimenting

If I got it right, you mounted the engine like everyone else.

Discounting the need for periodic low speed needle adjusting may turn out to be a mistake. It will probably need tweaks as the engine breaks in.
Old 04-30-2011, 07:21 PM
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Roary m
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Default RE: ST2300 Testing and Experimenting

I would like to put a 2300 in a GP Ryan STA-M. I would, however, like to have the cylinder facing down and was wondering if they made a Pitts style muffler to work facing down as well. Was toying with a canister muffler but they worry me in terms of back pressure. Any suggestions?
Old 04-30-2011, 10:29 PM
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Default RE: ST2300 Testing and Experimenting

Slimline Inverted Pitts for ST 2300
# S2112

this will do

V.
Old 05-03-2011, 03:22 PM
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Roary m
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Default RE: ST2300 Testing and Experimenting

Thank you much. I knew better than to post that about 2 minutes after I had, considering where I was sitting and what I was doing, duh.
Old 05-03-2011, 08:31 PM
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Default RE: ST2300 Testing and Experimenting


ORIGINAL: Roary m

Thank you much. I knew better than to post that about 2 minutes after I had, considering where I was sitting and what I was doing, duh.
[&o] ok i'm not getting this one...

BTW to have the same pressure as the original muffler, it is recommended to either block one of the two exhausts on the aftermarket inverted pitts, or [close] partially shut both exhaust (by putting the exhaust in a wice). Should work well.
Old 05-04-2011, 06:55 AM
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Default RE: ST2300 Testing and Experimenting


ORIGINAL: vasek


ORIGINAL: Roary m

Thank you much. I knew better than to post that about 2 minutes after I had, considering where I was sitting and what I was doing, duh.
[&o] ok i'm not getting this one...

He was referring to the fact that he was sitting at a computer with internet access and he could have looked it up for himself instead of posing the question here.
Old 05-08-2011, 04:39 PM
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Roary m
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Default RE: ST2300 Testing and Experimenting

I can't believe how hard it is to dig up one of these guys. Still looking, will call Tower in the A.M.
Old 08-20-2011, 02:25 PM
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Default RE: ST2300 Testing and Experimenting

Well, the 3250 didn't get much help from all those fixes I posted 4/30, but I did get a strong suggestion to sleeve the carb on another forum. I picked up a 3/8" barbed brass fitting for PEX tubing from Ho Depot and mounted it in my drill- filed it down on the OD to make it a light press fit in the carb's rotating barrel. Two bucks and two hours later, this brings the bore down to 10mm and now it gets much better fuel draw. I now can fly the plane reliably from a 2/3 fill (18 oz of a 24 oz tank) and am 20 tanks into loving it. Still gets iffy on a long down line or even landing approach in the first 4 minutes of the 10 minute flight. Iffy means if I hear it start to load up I can throttle up and recover.

BLW, I have my 3250 mounted sideways, pitts pipes down, and you were right about idle needle access. I DID need quite a bit of idle needle adjustment as it broke in. Only after that protracted 3 gal break-in was I able to mount the cowl, as I was frequently tweaking the idle needle for the first 3 gallons. Now it idles very nicely. After tuning many engines, I thought this one was untuneable, but a more experienced buddy watched me fly and suggested that the excessively rich idle was carrying so much fuel in the crankcase that the transition and even high end after 30 sec was affected. I was leaving the idle rich for break-in purposes. I sure wish you could pinch-tune the idle, but that does not seem to work for this engine.

So my vote for a balky 2300 (if it works for the 3250, 10mm is plenty for the 2300!) would be to replace the carb with one that has a 10mm airflow bore, or sleeve it the way I did, especially if you have little or no backpressure- i.e. when you are using an aftermarket Pitts Muffler. If you are not sure, and want to go getting all scientific, a manometer is easy to rig up to test the backpressure- just put a T fitting in the exhaust pressure line, and run a 4 foot piece of tubing in a U shape, with a 1 foot drop from the T fitting, then couple of feet going vertically above the fuel tank height. n I lashed mine to a 3' piece of pipe driven in the ground to hold it vertical.
Fill the U with ~2 ft of fuel, so that the U is filled 1 ft per side and fire the engine up. The difference in the two legs of the U when the engine is running ought to be at least 6 inches, better at 12 inches. 12 is equal to about 0.5 psi which I hear is ST's recommendation. I haven't got one of their factory mufflers, so I cannot confirm the "standard" Supertiger mufflers' backpressure.

Now that it's broken in, I just get it primed enough to be "squishy", say 5-7 cranks with the carb covered at full throttle, close the throttle to idle, flip it 7-10 times with no glow plug attached.
Then I hook up the glow, set the throttle up a click or two from dead idle and back flip it to start, i.e. not thru the compression stroke in normal direction, but just backwards enough to hit compression without going past TDC.
It basically backfires itself into starting forward 8/10 times! I had read about this, but never believed MY 3250 would ever be that loose and easy to start. It used to be 50x harder than this to start. The other 1/10 times it starts backwards, and 1/10 times I have to reprime it or it is too hot to restart so easily. Keep the faith is my message here- breakin counts for a lot on these engines in terms of starting and ildle. Burn a couple of gallons or even 4 gallons of 10% before your final verdict. Not such a cheap engine after that $60 in 10% fuel, but not a bad invesment once you are commited to the engine by buying it and cutting your cowl to it, eh?!?!? Besides, if you are a little daring and have a reliable gliding airframe, you can get a FEW minutes of joy in the air after the first gallon....
Old 08-20-2011, 11:17 PM
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Default RE: ST2300 Testing and Experimenting

Any pics of the mod? or a link to the original forum? thanks
Old 08-21-2011, 10:51 AM
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min$2crash
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Default RE: ST2300 Testing and Experimenting

Sure, Vasek, glad "the barber is still in"! I always try to post my final learnings to return the favor and hope it helps someone later.
The original forum was here:
http://www.rcuniverse.com/forum/m_44..._2/key_/tm.htm
Post #23 by flyer95 was the clincher for me. He had a 9mm bore carb working great on a SuperTigre S3000! I generally do NOT get into machining (whittling?) my own engine parts. I know how but no longer have lathe access.


And the Idle now sounds like this:
http://www.youtube.com/watch?v=M48Q8EBw7ks
But I attribute the nice idle to the break-in and final low needle adjustment. The sleeve mostly enhances fuel draw.


No pics of the mod, but installed, at WOT throttle position, you would just see a 1mm brass ring in the ID of the carb barrel. The 12mm carb bore hole thru the larger diameter rotating part of the carb leaves a saddle shaped surface at the OD top and bottom. I did not try to duplicate that shape. I just created the sleeve to stay well (~1mm)below that saddle shape so that it would not interfiere. I also tapered the ID of my bushing for ~ 2-3mm top & bottom for more of a venturi shape- that would be hard to show with pics. When the sleeve is in place, you drill the cross holes so that the hi & low needles can go thru the sleeve. I then pressed the "now finished" brass sleeve out for a brief deburr of those two new cross-bore holes (slightly different sizes as I recall) and reinstalled.
The fairly tight but free fitting (within a drill size, you could say!) cross-bore holes are the real keeper that I trust so that the sleeve can't come out partway and jam/interfere with the normal rotation of the carb barrel.

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