Super Tigre G3250 issue
07-17-2011, 01:42 PM
#26
RE: Super Tigre G3250 issue
I have been wrestling with a deadsticker 3250 on an old 1/3 scale Byron Pitts S-1 since November. I have owned and successfully tuned 18 of the 20 engines that I purchased new. 3 were SuperTigre 51's. The other "loser" was an MDS that cost me 3 gal of fuel barely flying with lots of deadsticks turned out to have the sleeve misaligned with the case but by the time I noticed that... 'nuff said. I had trouble finding a 7D carb, so I took your advice, FLYER95, and created a 10mm sleeve out of a $2 brass PE tubing fitting from Home Depot. Eventually, it worked! But it took another change to do it....
So, thanks, guys, for being persistent with the carb bore advice. I finally and vehemently agree! It seemed kinda crazy that the factory carb would (not) suck so, but heck!
I do not have a lathe, but do have an electric drill and a micrometer and a file, so I whittled the OD down to a light press in the barrel of the ST carb and drilled cross holes to clear the needle and seat. At first I thought that I had wasted my time, but it indeed added significant fuel draw to the carb. I can now run 10-12 minutes on 18 oz of fuel, flying at medium + power levels.
Hover, inverted, knife edge AOK.... long downlines are still an issue, but all in all a nice flying plane now
I am only filling the 24 oz tank part way (~19 oz) because it is so rich otherwise when the fuel is above the carb. Because I was sick of lean dead sticks 5 minutes into the flight I tuned the carb 1-2 clicks rich of peak with 2 oz in the tank and found it to be blubbery rich (barely flyable) at a full tank. So I flew it a few times that way, noting at what tank level it began to run well.
That is the level that I now fill it to! Not exactly rocket science, but it worked. :7) The tank's 2/3 mark is just about centered on the carb barrel's centerline, i.e. texbook position. So I am filling it to the height of the needle, no higher, in effect. So it is always forced to draw fuel, no gravity feed except in long downlines... which can be a problem.
I also think that it took 3-4 gallons of fuel to get the ST3250 broken in.....
I say that because now it idles beautifully slow and very reliably.
I now feel confident that it is broken in, and have swithced from 10% nitro Omega to the ST blend, 10% nitro but lower oil. Very happy now with either fuel.
I was about to "chuck-it" but am glad that I didn't now with the engine's performance.
I am flying a Byron Pitts with a modified** JTEC JT-100P muffler at 14.5 lbs dry and can climb out of hover a bit with a 22x8 Zinger wood prop cranking ~5500 rpm. Gadzooks!
Prior to the sleeve and change in tank level I did many things which I found on many forums and verbally at the airfield:
Needled the heck out of it each time to no avail!
OS#8, OS"F", Enya #3 and Fox RC long idlebar plugs (Fox in there now working just fine).
Drilled the inlet nipple larger
Cleaned a bit of rust off of the main needle.
"glued" or sealed the brass needle holder in place with red RTV to avoid leaks there
deburred the brass needle holder first....
Remounted the carb with care to use a large clamp to get extra "squeeze" on the O-ring before tightening the jamb screw to keep it in place
Turned the brass needle holder to align with the carb throat
Turned it ~3-5° so the cat's eye was forward and tried it the same amount backward
Went to a bubbleless clunk (brass beads type)
Plugged one pitts muffler outlet (the closer one where all the exhause goes) and measured backpressure with a homemade manometer to be 0 still. I read somewhere that ST recommends 0.5 psi backpressure which would be 1ft of water on my homemade u-tube manometer. I got no pressure at all- not even 1/8".
Needled it nose up....too rich to stay running when level.
Bottom line, I think that, other than eliminating possibilities most of this was uneccesary. I was about to put a Perry pump on it after the 10mm sleeve didn't pan out but thought that may just add worries. I was going to have to drill and tap the backplate mount (cone) to mount it and would've been at a much larger distance from the crank than the instructions recommended.
So, after sleeving the factory carb down to 10mmØ I tried needling it for the bottom of the tank, & then it started OK with a full tank, but was blubbery as heck for 5-7 minutes before it ran well. That's what made me want to try the partial fill. I had read where many folks needle their engine at half a tank- I had always just taergeted rich on a full tank.
The moral of the story is that the needle meters flow, but can only handle so much variation in tank level. Even with a sleeve to get decent draw, the normal tank position was too high.
The other moral of the story is that there are many ideas, but it can take a lot of patience to get to the one or combination of 2 or 3 ideas that works out. Complex system, I guess!
I know that I am posting this a bit late, i.e. way after the last post, but just wanted to leave this tidbit for any future travelers and for anyone who has subscribed to this thread.
Because.... Truth stands the test of time!
CHeck out that idle now!!
http://www.youtube.com/watch?v=M48Q8EBw7ks
** I had to add~10" of pipe to each outlet so that the Pitts plane had a decent looking Pitts muffler outlet location!!
So, thanks, guys, for being persistent with the carb bore advice. I finally and vehemently agree! It seemed kinda crazy that the factory carb would (not) suck so, but heck!
I do not have a lathe, but do have an electric drill and a micrometer and a file, so I whittled the OD down to a light press in the barrel of the ST carb and drilled cross holes to clear the needle and seat. At first I thought that I had wasted my time, but it indeed added significant fuel draw to the carb. I can now run 10-12 minutes on 18 oz of fuel, flying at medium + power levels.
Hover, inverted, knife edge AOK.... long downlines are still an issue, but all in all a nice flying plane now
I am only filling the 24 oz tank part way (~19 oz) because it is so rich otherwise when the fuel is above the carb. Because I was sick of lean dead sticks 5 minutes into the flight I tuned the carb 1-2 clicks rich of peak with 2 oz in the tank and found it to be blubbery rich (barely flyable) at a full tank. So I flew it a few times that way, noting at what tank level it began to run well.
That is the level that I now fill it to! Not exactly rocket science, but it worked. :7) The tank's 2/3 mark is just about centered on the carb barrel's centerline, i.e. texbook position. So I am filling it to the height of the needle, no higher, in effect. So it is always forced to draw fuel, no gravity feed except in long downlines... which can be a problem.
I also think that it took 3-4 gallons of fuel to get the ST3250 broken in.....
I say that because now it idles beautifully slow and very reliably.
I now feel confident that it is broken in, and have swithced from 10% nitro Omega to the ST blend, 10% nitro but lower oil. Very happy now with either fuel.
I was about to "chuck-it" but am glad that I didn't now with the engine's performance.
I am flying a Byron Pitts with a modified** JTEC JT-100P muffler at 14.5 lbs dry and can climb out of hover a bit with a 22x8 Zinger wood prop cranking ~5500 rpm. Gadzooks!
Prior to the sleeve and change in tank level I did many things which I found on many forums and verbally at the airfield:
Needled the heck out of it each time to no avail!
OS#8, OS"F", Enya #3 and Fox RC long idlebar plugs (Fox in there now working just fine).
Drilled the inlet nipple larger
Cleaned a bit of rust off of the main needle.
"glued" or sealed the brass needle holder in place with red RTV to avoid leaks there
deburred the brass needle holder first....
Remounted the carb with care to use a large clamp to get extra "squeeze" on the O-ring before tightening the jamb screw to keep it in place
Turned the brass needle holder to align with the carb throat
Turned it ~3-5° so the cat's eye was forward and tried it the same amount backward
Went to a bubbleless clunk (brass beads type)
Plugged one pitts muffler outlet (the closer one where all the exhause goes) and measured backpressure with a homemade manometer to be 0 still. I read somewhere that ST recommends 0.5 psi backpressure which would be 1ft of water on my homemade u-tube manometer. I got no pressure at all- not even 1/8".
Needled it nose up....too rich to stay running when level.
Bottom line, I think that, other than eliminating possibilities most of this was uneccesary. I was about to put a Perry pump on it after the 10mm sleeve didn't pan out but thought that may just add worries. I was going to have to drill and tap the backplate mount (cone) to mount it and would've been at a much larger distance from the crank than the instructions recommended.
So, after sleeving the factory carb down to 10mmØ I tried needling it for the bottom of the tank, & then it started OK with a full tank, but was blubbery as heck for 5-7 minutes before it ran well. That's what made me want to try the partial fill. I had read where many folks needle their engine at half a tank- I had always just taergeted rich on a full tank.
The moral of the story is that the needle meters flow, but can only handle so much variation in tank level. Even with a sleeve to get decent draw, the normal tank position was too high.
The other moral of the story is that there are many ideas, but it can take a lot of patience to get to the one or combination of 2 or 3 ideas that works out. Complex system, I guess!
I know that I am posting this a bit late, i.e. way after the last post, but just wanted to leave this tidbit for any future travelers and for anyone who has subscribed to this thread.
Because.... Truth stands the test of time!
CHeck out that idle now!!
http://www.youtube.com/watch?v=M48Q8EBw7ks
** I had to add~10" of pipe to each outlet so that the Pitts plane had a decent looking Pitts muffler outlet location!!
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leonardor (08-17-2020)
07-24-2011, 10:00 AM
#29
RE: Super Tigre G3250 issue
12mm sounds like the most common carb for the Big Cats (ST 2300 &up) which all sport a 12mm airflow bore. No first hand knowledge on this for the 2300 as I only have the 3250. But my experience with tank level was that there was not a single good high needle setting for both full and bottom of tank, even after sleeving the ST carb down to 10mm diameter bore. The fix for mine was a partial tank fill, only putting about 18-20 oz in a 24 oz tank. My 18-20 oz fuel level is just above the carb bore at that point.
The sleeved barrel creates fuel draw, but hi tank level floods it too much. My case is special in that I have no muffler back pressure because my Jtec muffler was 0 psi back pressure even with one pipe plugged.
That's why I went to the trouble of sleeving it.
I was also not interested in spending $45 on an engine that I bought from a friend "barely used" for $100 to go on a plane I paid $20 for.....
I have expensive projects and this is not one of them!
Page 5 at CLUB SUPER TIGER has a bit on this. Flyer95 talks about 9mm bore there. I am doing OK with 10mm after sleeving the carb throat down from 12mm. 9 would be easier to make, as the wall thickness on mine is just 1mm!
The sleeved barrel creates fuel draw, but hi tank level floods it too much. My case is special in that I have no muffler back pressure because my Jtec muffler was 0 psi back pressure even with one pipe plugged.
That's why I went to the trouble of sleeving it.
I was also not interested in spending $45 on an engine that I bought from a friend "barely used" for $100 to go on a plane I paid $20 for.....
I have expensive projects and this is not one of them!
Page 5 at CLUB SUPER TIGER has a bit on this. Flyer95 talks about 9mm bore there. I am doing OK with 10mm after sleeving the carb throat down from 12mm. 9 would be easier to make, as the wall thickness on mine is just 1mm!
