pinch test
08-27-2010, 08:52 PM
#1
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pinch test
when i did my pinch test on my 75 ax it died right away so i richened it a little at a time until i got it too rich and there was still no difference,so i screwed the needle all the way back in and turned it out 2 1/4 turns and started it again tuned it a little and did the pinch test again and it died again i continued to richen it a little at a time and still no luck with the pinch test! what should i do now?
08-27-2010, 09:07 PM
#2
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RE: pinch test
The pinch test is for setting the lowspeed needle, right?
Both times you richened it because you thought it died right away. And that didn't work.
Quit pinching because it's either not working with your pinches, or you're not hearing it right, or something very out of the ordinary is happening.
Simply start from that base setting again. Instead of doing any test at all, simply turn it in about 1/8 turn and try the throttle. Keep that up and you'll see improvement eventually or the lowspeed needle will wind up closed. That will tell you that it's not too rich. The last two OS I've broken in both had a really badly set lowspeed needle, over a turn too rich.
There is a chance you're not doing something that needs to be done every pinch test. You've got to run the engine at full throttle to warm it on your first try. Then every try you've got to clear out overprime that came when starting for that run. Each time you restart the engine, advance the throttle to wide open and let it settle. Letting it settle clears excess prime. THEN back it down to idle and let that run a bit before pinching. If you don't clear out the engine before the pinch, you won't get good results..
Both times you richened it because you thought it died right away. And that didn't work.
Quit pinching because it's either not working with your pinches, or you're not hearing it right, or something very out of the ordinary is happening.
Simply start from that base setting again. Instead of doing any test at all, simply turn it in about 1/8 turn and try the throttle. Keep that up and you'll see improvement eventually or the lowspeed needle will wind up closed. That will tell you that it's not too rich. The last two OS I've broken in both had a really badly set lowspeed needle, over a turn too rich.
There is a chance you're not doing something that needs to be done every pinch test. You've got to run the engine at full throttle to warm it on your first try. Then every try you've got to clear out overprime that came when starting for that run. Each time you restart the engine, advance the throttle to wide open and let it settle. Letting it settle clears excess prime. THEN back it down to idle and let that run a bit before pinching. If you don't clear out the engine before the pinch, you won't get good results..
08-27-2010, 09:09 PM
#3
RE: pinch test
Why the pinch test?
Is this your first try with glow engines?
Start working your way from over rich to less and less rich.
Pinch test is for fine tune around the limit, which is close to the "too lean" condition.
Take a look at the explanations here:
http://www.gettingairborne.com/engines.html
Is this your first try with glow engines?
Start working your way from over rich to less and less rich.
Pinch test is for fine tune around the limit, which is close to the "too lean" condition.
Take a look at the explanations here:
http://www.gettingairborne.com/engines.html
08-28-2010, 07:31 AM
#6
My Feedback: (1)
RE: pinch test
First, what size prop are you using? OS tends to suggest props a bit too heavy which makes the high speed needle overly critical. Also you are better off with the needle opened more than 2 1/4 turns when starting a new engine. Set the initial position 3 turns from when you can first hear air going through the needle seat with the carb wide open. You will find that position is different from where the needle quits turning. Just blow through the fuel line and listen carefully.
Finally, when you do the pinch test (high speed test at wide open throttle), you pinch and release the fuel line as fast as you can. All you are looking for is a momentary increase in speed.
Finally, when you do the pinch test (high speed test at wide open throttle), you pinch and release the fuel line as fast as you can. All you are looking for is a momentary increase in speed.
08-28-2010, 09:46 AM
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RE: pinch test
I've never really used the pinch test on my 46fx or 95ax when initially setting low speed mixture. I just let it idle for 10 seconds and then move it to full throttle quickly. If it spits or sputters, I'll lean it out a 1/12 of a turn. If it immediately dies, I'll richen it up 1/12 of a turn and try again. Once I get it to how I like it, I'll go full throttle and give it a quick pinch test to see what it does.
For my O.S. engines, I've never had luck with the #8 plug. I had to use a hotter A3 plug in the .46 and an OSF for the 95AX.
For my O.S. engines, I've never had luck with the #8 plug. I had to use a hotter A3 plug in the .46 and an OSF for the 95AX.
08-28-2010, 11:54 AM
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RE: pinch test
I'll bet you richened the high speed needle.....the needle that sticks up......the pinch test is for the low end the screw that is inside the throttle arm
08-28-2010, 12:04 PM
#9
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RE: pinch test
In all the pinch tests I've ever seen or done, it deals with the high speed adjustment only. Turn the needle valve to get what you think is the maximum safe RPM. Now pinch off the line to the needle valve. If the engine dies quickly, it is set to lean. If it slightly speeds up then dies, it is just right. The pinch test has nothing to do with the low speed needle valve adjustment.
08-31-2010, 12:47 PM
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RE: pinch test
I dont bother with pinch test. I oppen the throttle to max then adjust untill the engine reaches max rpm then turn the needle 1/4 turn rich. After that i try the model pointing up and down and trim untill the engine keeps running
09-01-2010, 08:21 PM
#13
RE: pinch test
I was taught to use the pinch test by allowing the engine to warm up a bit then running up to full throttle and holding it there for a few seconds to clear out the engine. I then run it back to idle for a few seconds, then back to full throttle. That's when I do the pinch test and set the idle always working to rich and back to a tad bit leaner. I never leave the engine in a tune point where it is lean. I check it a couple of times, even to the point where I put it to blubbering rich for a moment to make sure that it's set right.
When I start out, the high speed needle was originally set to about 2.5 turns out from full closed, which always has been appropriate for the initial start and a good starting point for the tune.
I have use a pinch test at low speed, but not often. I use it mostly at high speed and, with a good practiced ear, I seem to get it right.
CGr.
When I start out, the high speed needle was originally set to about 2.5 turns out from full closed, which always has been appropriate for the initial start and a good starting point for the tune.
I have use a pinch test at low speed, but not often. I use it mostly at high speed and, with a good practiced ear, I seem to get it right.
CGr.
09-01-2010, 11:33 PM
#14
RE: pinch test
Tunning to a pinch I beleve originally came from the high performance free flight fellows and migrated to the pylon crowd where it is very common and where I picked it up.
It is an acquired technique that does require some sound interpretation but is not only very accurate but can be accomplished in seconds easily. It is so fast that you can completely needle the high speed in just seconds with no aids such as tacks or need to keep flailing the airplane up in the air blowing dust and stuff on everone in sight. More importantly is so fast that you do not get poor needles that is typical when sitting there overheating the engine in a long drawn out procedure and gunning the engine. It is like CGR said just done simply by running the engine up WOT letting it stabilize and pinch the tank line just for a fraction of a second almost as quickly as you can do it. Its more obvious than all the other methods on which way you need to turn the needle and multiple pinchs and tweeks of the needle can be done in one quick WOT and your done.
It works and I teach it to any in earshot and the fellows I am mentoring. It is the most used method here now and consistancy of the result becomes noticible over time. It is not as effective with four strokes and for them recommend using more convertional techniques.
So for all my fleet that uses two strokes (the majority) I alway make sure that there is easy accessability to the carb feed line even with cowled installation to facultate easy pinching.
John
It is an acquired technique that does require some sound interpretation but is not only very accurate but can be accomplished in seconds easily. It is so fast that you can completely needle the high speed in just seconds with no aids such as tacks or need to keep flailing the airplane up in the air blowing dust and stuff on everone in sight. More importantly is so fast that you do not get poor needles that is typical when sitting there overheating the engine in a long drawn out procedure and gunning the engine. It is like CGR said just done simply by running the engine up WOT letting it stabilize and pinch the tank line just for a fraction of a second almost as quickly as you can do it. Its more obvious than all the other methods on which way you need to turn the needle and multiple pinchs and tweeks of the needle can be done in one quick WOT and your done.
It works and I teach it to any in earshot and the fellows I am mentoring. It is the most used method here now and consistancy of the result becomes noticible over time. It is not as effective with four strokes and for them recommend using more convertional techniques.
So for all my fleet that uses two strokes (the majority) I alway make sure that there is easy accessability to the carb feed line even with cowled installation to facultate easy pinching.
John
09-01-2010, 11:51 PM
#15
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RE: pinch test
This is a great explanation. You can use a version of the pinch test for low end, or you can just idle for 20 sec or so, rapidly throttle up and see if it bogs down / stalls.
http://www.rcgroups.com/forums/showthread.php?t=205602
I know the link is for another site, but the info is useful!
http://www.rcgroups.com/forums/showthread.php?t=205602
I know the link is for another site, but the info is useful!
09-02-2010, 10:24 AM
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RE: pinch test
ORIGINAL: DenverJayhawk
I've never really used the pinch test on my 46fx or 95ax when initially setting low speed mixture. I just let it idle for 10 seconds and then move it to full throttle quickly. If it spits or sputters, I'll lean it out a 1/12 of a turn. If it immediately dies, I'll richen it up 1/12 of a turn and try again. Once I get it to how I like it, I'll go full throttle and give it a quick pinch test to see what it does.
For my O.S. engines, I've never had luck with the #8 plug. I had to use a hotter A3 plug in the .46 and an OSF for the 95AX.
I've never really used the pinch test on my 46fx or 95ax when initially setting low speed mixture. I just let it idle for 10 seconds and then move it to full throttle quickly. If it spits or sputters, I'll lean it out a 1/12 of a turn. If it immediately dies, I'll richen it up 1/12 of a turn and try again. Once I get it to how I like it, I'll go full throttle and give it a quick pinch test to see what it does.
For my O.S. engines, I've never had luck with the #8 plug. I had to use a hotter A3 plug in the .46 and an OSF for the 95AX.
Hey DJ a little surprised to hear of your problem with the #8 plug. I have gone with an OSF on inverted 2 stokes with good success.
09-02-2010, 11:31 AM
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RE: pinch test
ORIGINAL: Augie11
DJ actually uses the method recommended in the manufacturer's instructions for setting the low speed needle. How refreshing! Imagine if someone next suggested using a tach to get the right high speed needle adjustment and then backing off 200 rpm to fly? I haven't used the pinch test in 20 years.....about the same time I had my last in-flight dead stick.
Hey DJ a little surprised to hear of your problem with the #8 plug. I have gone with an OSF on inverted 2 stokes with good success.
ORIGINAL: DenverJayhawk
I've never really used the pinch test on my 46fx or 95ax when initially setting low speed mixture. I just let it idle for 10 seconds and then move it to full throttle quickly. If it spits or sputters, I'll lean it out a 1/12 of a turn. If it immediately dies, I'll richen it up 1/12 of a turn and try again. Once I get it to how I like it, I'll go full throttle and give it a quick pinch test to see what it does.
For my O.S. engines, I've never had luck with the #8 plug. I had to use a hotter A3 plug in the .46 and an OSF for the 95AX.
I've never really used the pinch test on my 46fx or 95ax when initially setting low speed mixture. I just let it idle for 10 seconds and then move it to full throttle quickly. If it spits or sputters, I'll lean it out a 1/12 of a turn. If it immediately dies, I'll richen it up 1/12 of a turn and try again. Once I get it to how I like it, I'll go full throttle and give it a quick pinch test to see what it does.
For my O.S. engines, I've never had luck with the #8 plug. I had to use a hotter A3 plug in the .46 and an OSF for the 95AX.
Hey DJ a little surprised to hear of your problem with the #8 plug. I have gone with an OSF on inverted 2 stokes with good success.
09-02-2010, 06:51 PM
#18
RE: pinch test
The OS-F is a "four-stroke" plug, right? Just asking. Perhaps that's why it works better.. has to be hot to endure the latency between the cycles. Yeah, it seems that I use the F plug a lot too.
There is no magic bullet here.. just a lot or experimentation that we have to do to find out what works for each of us under our flying conditions. What works for one may not work for another. We try to pass on as much good and useful information that we have under our particular circumstances... altitude, weather, temperature, flying style... and all that stuff.
CGr.
There is no magic bullet here.. just a lot or experimentation that we have to do to find out what works for each of us under our flying conditions. What works for one may not work for another. We try to pass on as much good and useful information that we have under our particular circumstances... altitude, weather, temperature, flying style... and all that stuff.
CGr.
09-02-2010, 07:32 PM
#19
My Feedback: (-1)
RE: pinch test
ORIGINAL: JohnBuckner
Tunning to a pinch I beleve originally came from the high performance free flight fellows and migrated to the pylon crowd where it is very common and where I picked it up.
It is an acquired technique that does require some sound interpretation but is not only very accurate but can be accomplished in seconds easily. It is so fast that you can completely needle the high speed in just seconds with no aids such as tacks or need to keep flailing the airplane up in the air blowing dust and stuff on everone in sight. More importantly is so fast that you do not get poor needles that is typical when sitting there overheating the engine in a long drawn out procedure and gunning the engine. It is like CGR said just done simply by running the engine up WOT letting it stabilize and pinch the tank line just for a fraction of a second almost as quickly as you can do it. Its more obvious than all the other methods on which way you need to turn the needle and multiple pinchs and tweeks of the needle can be done in one quick WOT and your done.
It works and I teach it to any in earshot and the fellows I am mentoring. It is the most used method here now and consistancy of the result becomes noticible over time. It is not as effective with four strokes and for them recommend using more convertional techniques.
So for all my fleet that uses two strokes (the majority) I alway make sure that there is easy accessability to the carb feed line even with cowled installation to facultate easy pinching.
John
Tunning to a pinch I beleve originally came from the high performance free flight fellows and migrated to the pylon crowd where it is very common and where I picked it up.
It is an acquired technique that does require some sound interpretation but is not only very accurate but can be accomplished in seconds easily. It is so fast that you can completely needle the high speed in just seconds with no aids such as tacks or need to keep flailing the airplane up in the air blowing dust and stuff on everone in sight. More importantly is so fast that you do not get poor needles that is typical when sitting there overheating the engine in a long drawn out procedure and gunning the engine. It is like CGR said just done simply by running the engine up WOT letting it stabilize and pinch the tank line just for a fraction of a second almost as quickly as you can do it. Its more obvious than all the other methods on which way you need to turn the needle and multiple pinchs and tweeks of the needle can be done in one quick WOT and your done.
It works and I teach it to any in earshot and the fellows I am mentoring. It is the most used method here now and consistancy of the result becomes noticible over time. It is not as effective with four strokes and for them recommend using more convertional techniques.
So for all my fleet that uses two strokes (the majority) I alway make sure that there is easy accessability to the carb feed line even with cowled installation to facultate easy pinching.
John
09-02-2010, 07:58 PM
#20
RE: pinch test
Gene.. my instructor pretty well drilled in the pinch test when I was learning. He pointed out that it was always better to make it a tad bit rich. So, I got the "ear" and seem to have had pretty good success that way. I would do the test then end up with a tad bit of rich, perhaps a click or two.
When I started out, I had quite a few dead-sticks about half way throught the flight. When I landed it, he worked with me to show me the differences between where I had set it and where it should be. and that all was "the ear"... the tone of the engine note during the pinch test.
Since I got it down, I've not had dead-sticks due to mixture settings. It works for me, but may not work for others.
I guess information given in these forums allows folks to work it out and see what works best for him/her.
CGr.
When I started out, I had quite a few dead-sticks about half way throught the flight. When I landed it, he worked with me to show me the differences between where I had set it and where it should be. and that all was "the ear"... the tone of the engine note during the pinch test.
Since I got it down, I've not had dead-sticks due to mixture settings. It works for me, but may not work for others.
I guess information given in these forums allows folks to work it out and see what works best for him/her.
CGr.
09-02-2010, 09:26 PM
#21
RE: pinch test
ORIGINAL: JohnBuckner
It is an acquired technique that does require some sound interpretation but is not only very accurate but can be accomplished in seconds easily.
...........just done simply by running the engine up WOT letting it stabilize and pinch the tank line just for a fraction of a second almost as quickly as you can do it.
It is an acquired technique that does require some sound interpretation but is not only very accurate but can be accomplished in seconds easily.
...........just done simply by running the engine up WOT letting it stabilize and pinch the tank line just for a fraction of a second almost as quickly as you can do it.
Before today, I have used the pinch only for adjusting low end.
Thanks to your post, I tried the pinch for high end this evening at the field.
I believe that I improved the performance of my 0.40 engine that way.
However, I had to pinch the line a little longer than what you have explained, in order to hear the small increment in rpm's.
My needle valve is not remote.
09-02-2010, 11:18 PM
#22
RE: pinch test
You are welcome. Lag times and therefore the duration of your pinch will vary from engine type to engine type but that is soon corrected for with a little practice but then what is important is to always use the same duration each time.
I find this technique makes it possible and easy to choose operation closer to peak or a more conservative mixture and do it much more accurately than reaching peak then backing off some arbitrary RPM figure that may or may not even be whats needed for any particular engine and set of conditions (temperature, density altitude and humidity) .
John
I find this technique makes it possible and easy to choose operation closer to peak or a more conservative mixture and do it much more accurately than reaching peak then backing off some arbitrary RPM figure that may or may not even be whats needed for any particular engine and set of conditions (temperature, density altitude and humidity) .
John
09-02-2010, 11:27 PM
#23
My Feedback: (-1)
RE: pinch test
ORIGINAL: CGRetired
Gene.. my instructor pretty well drilled in the pinch test when I was learning. He pointed out that it was always better to make it a tad bit rich. So, I got the ''ear'' and seem to have had pretty good success that way. I would do the test then end up with a tad bit of rich, perhaps a click or two.
When I started out, I had quite a few dead-sticks about half way throught the flight. When I landed it, he worked with me to show me the differences between where I had set it and where it should be. and that all was ''the ear''... the tone of the engine note during the pinch test.
Since I got it down, I've not had dead-sticks due to mixture settings. It works for me, but may not work for others.
I guess information given in these forums allows folks to work it out and see what works best for him/her.
CGr.
Gene.. my instructor pretty well drilled in the pinch test when I was learning. He pointed out that it was always better to make it a tad bit rich. So, I got the ''ear'' and seem to have had pretty good success that way. I would do the test then end up with a tad bit of rich, perhaps a click or two.
When I started out, I had quite a few dead-sticks about half way throught the flight. When I landed it, he worked with me to show me the differences between where I had set it and where it should be. and that all was ''the ear''... the tone of the engine note during the pinch test.
Since I got it down, I've not had dead-sticks due to mixture settings. It works for me, but may not work for others.
I guess information given in these forums allows folks to work it out and see what works best for him/her.
CGr.
Just for grins. Yesterday I broke in a new .46AX for a friend. After the break in runs I took a tach to it and had it set on the ground 500 RPM fat. One guy in the pits was freaking out because it didn't have a huge smoke trail, I could see smoke but with the 100% synthetic oil no mater how much fatter I ran it the trail wasn't good enough for the peanut gallery. No one else had a clue what fuel I was using but I learned I had to have a huge smoke trail or the engine was too lean. I always thought you tuned the engine, not the smoke?? I stuck in a tank of my Powermaster and it was decided the engine was in correct tune. I never touched the NV. My bad but I thought it was funny!
