goofy_txn

My Feedback: (1)

This is my first 4stoker satio 120 and I trying to figure out how to pich test the fuel line for proper air fuel mixture. It this right...........

(with throttle wide open) Pinch and release the incomming fuel line and if.........

The RPM slows down and return to and idle the mixture is "Rich"
The RPM speed up and return to idle the mixture is "Lean"
The RPM stays the same the mixture is "OK"

Is this right?

goofy_txn

My Feedback: (1)

(with throttle wide open) Pinch and release the incomming fuel line and if.......

The RPM increase and does not return, then what does that mean?
If the PPM decreases and does not retrun the what does that mean?

quint-rcu

My Feedback: (24)

I've never done a 'pinch' test to check full speed mixture, but rather set it with a tach to about 200 to 300 RPM down from full speed to the rich side. Then if you want to confirm it, you can point the nose straight up for a few seconds at full throttle to verify it doesn't go lean on climb. I use the 'pinch' test to check the low speed idle mixture. - If it drops with a three second pinch, it's lean and if it increases with a three second pinch, it's too rich. Make idle mixture adjustments in 1/4 turn or so increments as it is critical.

quint

daveopam

My Feedback: (9)

The pinch dosn't work as well on a 4C like it dose on a 2C. A 4C can pass the pinch test and still be lean. The best way is with a tach.
Once you get it set you rarley have to touch the needle. Just lean it to max RPM then richen it 300-400RPM.

I hope this helps. I intentionaly did not answer your specific questions because you can lean out and hurt the motor.
Once you get used to it it can be tuned be ear. It takes a little time to get used to it.

David

Homebrewer

My Feedback: (8)

I don't understand how it can pass a pinch test and still be too lean. The purpose of the pinch test is confirm a mixture setting that is 300-400 rich of max lean rpm.

Once you set your mixture with a tach (300-400 rpm shy of max lean rpm) on subsequent flights using a tach (takes 5 seconds and worth the time investmetn), pinch and release the fuel line at wide open throttle to verify that engine speeds up 300-400 rpm and comes back down. This means the engine is at the desired mixture setting.

For setting the idle mixture, the pinch test is not recommended to set the mixture. Some 4 strokes prefer to run very rich at idle while others run rather lean with no problem. You'll have to fine tune your low end needle to obtain the optimum performance with your engine by making small incremental adjustments.

For 2 stroke engines, the pinch test is a great way (no tach needed) to verify a mixture setting after it has been set. It is also a good way to set your low end needle into a ballpark setting for fine tuning.

Do a search here with my username and pinch test for the info you seek. No need to repeat it, it has been posted many times.

paladin

My Feedback: (9)

I'm rather new to four cycles but the method I use is:

Let the engine warm up, then move it so that nobody is inline with the prop.. I usually do this by moving half way between the pits and the flight line. Or at the flightline point the planes prop. away from others.

At full throttle turn the high speed needle to richen until I here the engine labor, then reverse and turn lean until I here the engine labor then set the needle in the center of those two points. I've also found that the distence between lean and rich changes with temp. And humidity. On a cold dry day there may be a full turn between, while on a hot humid day there my be only be ½ a turn between rich and lean.

I fly at two fields that have a 700ft altitude difference which required adjusting high speed each time out (two clicks difference on a 2 cycle). I have been doing the process above for the four strokes so I don't know if there is a click count.

Just my two cents

Joe Felice

FlyingPilgrim

My Feedback: (26)

Like Dave said above, don't use the pinch test for a 4-stroke. Get a tach and do it as he said (300-400 below peak rpm for high speed needle). It's too hard to hear small changes in rpm with a 4-stroke, don't take the risk of running it too lean. Pinch test is only for 2-strokes.

Pilgrim

Geistware

My Feedback: (16)

I do not recommending pinch testing a 4 stroke.
You can damage the engine, spinner, or throw the propeller.

rc-sport

My Feedback: (12)

I have only 4 strokes and I always use the pinch test on the low setting and I have not ruined an engine, spinner or thrown a prop. What I do have have is 8 4 strokes that tick like clocks on idle, transition to full throttle in a heartbeat without a hiccup. I do use a tach on the high end.