engine tuning - pinch test
 

I've watched several of my instuctors tune my engine while I was training. Now that I"ve solo'ed and and flying on my own sometimes there aren't people out at the field to help me tweak it I'm trying to learn how to a little better. I think I've got the basic theory. Tune high end - pinch test should sound stable rpm or just slightly speed up with throttle wide open. and essentially the same for the low end at approx idle after the high end is done. Is this anything near correct? Where do I pinch. between tank and needle valve for between needle valve and throttle and carb?

RE: engine tuning - pinch test
 

Pinch test with the engine wide open and running smooth, you pinch the fuel line to the needle very quickly and release. The engine should speed up slightly. If too lean, when you pinch, the engine will sag slightly. Also if you have a typical trainer, the tank is too low, so you will want to set the engine richer yet. Tanks SHOULD BE mounted with the centerline no more than 1/4 to 3/8" lower than the needle valve. Most trainers fail this measurement, and you end up cooking the motors.

Idle, you set by how it responds to throttle. Usually, most engines will need to be leaned slightly after the engine break-in. Slightly is about 1/16 to 1/8 of a turn.

If you start having trouble with the idle, it could be the plug, or the engine is getting varnished and needs cleaning. Crock pot and antifreeze works the best. Look it up to find out more with the search function.

RE: engine tuning - pinch test
 

I've been instructing for quite awhile now, and have seen most of the major trainers out there, and this just isn't true. While the tank isn't always "exact" you're definitely not going to "cook" the engine by any means.

Huh?? How do you figure that varnish on the engine affects the way the engine preforms to a pinch test? Having a bit of varnish on an engine can cause it to run a bit hotter, but not enough to make any major changes in how the engine performs. Especially for a beginner that has a fairly new engine. They just haven't had the engine running long enough to build up much varnish on it.

Ken

RE: engine tuning - pinch test
 

I've been at this for a very long time too, 36 years of RC with another 10 of U-control before than. Most trainers have the tank too low for a good needle setting, so one needs to set richer than what you would if the tank was in the correct positon. I see far more sport fliers cook their engines than I ever see operate them correctly. Most instructors are clueless too, since they only do what they were taught.

You might re-read where I was talking about IDLE and the effects of varish. Plus, from some of the posts here, some are beginners for a very long time.

RE: engine tuning - pinch test
 

I will throw somethng in here on the low end. many use it and works well. It's for getting the low end set right. You have to be careful though. There are back up checks to see if the adjustments you made had an effect, wheter good or bad. That pinch test n the high end is one of them. For the low end, do this,

While the engine is at an idle, either remove the fuel line from the carb or pinch it closed until the engine quits running. Trick is to listen to the rpms as the engine dies. If the rpms increase and then go down and quit. your low end is too rich. If the rpms just go down and quit-too lean. I usually set mine at a very slight increase. I rarely change my low end in any single weather season.

Have not had a deadstick in several years due to tuning issues.

RE: engine tuning - pinch test
 

Cyclic,

Best part of your idle method is that the engine is stopped for adjustment. As it should be.

RE: engine tuning - pinch test
 

Oh heck ya, Ah may be stupid but not an idiot:D I see many guys come out with new planes for maidens with the cowls on and tune them up. These are good friends and know what they're doing but even though it may sound great and they're happy, it can still be way off. I just thinks it's best to show up at the field with the cowl off and spend a couple tanks full on getting it right the first time.

RE: engine tuning - pinch test
 

"Pay no attention to the man behind the curtain" That's Right!
Just tune for peak, then richen it up three clicks. You'll be fine right there.
Bob

RE: engine tuning - pinch test
 

I guess you can count me as one of those clueless types, since I do what I was taught. Of course one of my instructors was flying masters at the time, and continues to be active at high levels of competition. What he, and MANY others taught me is that the "pinch test" is a very inaccurate method of checking for proper high speed mixture. The first reason is nobody's going to pinch the fuel line when the plane is in the air. Second, what constitutes a proper pinch? Is it .1 second, .5 second, or what? Bottom line, it's inaccurate, and teaching this method is a disservice to others. A far better test is pointing the nose of the plane vertical to see how the engine reacts. This simulates something that the plane is actually going to do in the air and will yield far more accurate results than a pinch.
I've got engines that are over 25 years old. They continue to work as well today as when they were new. They've never been subjected to an antifreeze treatment, and probably never will. There are many reasons an engine could have idle problems, and it's hard to imagine jumping from plug replacement to an antifreeze bath without looking at other causes. In fact, it's a bit hard to imagine such a suggestion in response to a simple request for information on tuning an engine.

One other observation. Since today's fuels contain much less, or no, castor, varnish buildup is much less common than it was 25-30 years ago.

RE: engine tuning - pinch test
 

Well, since the original question was on how to do the "pinch test" -- that was asked and answered.

RE: engine tuning - pinch test
 

Setting the motor rich causes it to get "cooked"? If a motor is indeed running rich then it's exactly the opposite of being "cooked". Running a motor rich causes it to run cooler because of the excess liquid running through the engine removes heat from the engine. It's when an engine is ran too lean that it gets cooked.

Ok, let's step back and read the whole statement you made about the idle

Ok, I don't see anywhere that you state the effects of varnish on the idle. You make the statement that the "engine is getting varnished", but you said nothing about how it effects the idle. As it is I will stand behind my statement that the varnish on the engine has nothing to do the situation at hand.

Well thank you so much for setting that straight as I was clueless about it. Oh yeah, that figures because I'm an instructor. :D Regardless of how long you have been in the hobby I will ask if YOU are an instructor. Are you?? Do you take the time out to pass down the huge wealth of knowledge to new people in the hobby??? If you do then I will say good job for helping. If you don't then I will tell you that you're not part of the solution you are part of the problem. Those that take the time out to help new people in the hobby both at the flying field and here on RCU deserve a huge pat on the back. It takes an incredible amount of time out of somebodies day to teach a new student, and those that do so do it because they LOVE this hobby and want to share that with new people. They spend an incredible amount of time here on RCU in this forum answering the questions of the beginners as they get started in this hobby, often time answering the same questions over and over again. Once again, they do this because of a love for this hobby. It's the new people getting in the hobby that keep this hobby going, trust me that without them the hobby would dry up and be gone. I can assure you that the hobby manufacturers would not be investing time and money into this market if there wasn't a prospective group of buyers coming up. They wouldn't stay here if were only the "old farts" left in the hobby. They would close up shop and do something else. So it's the new people that keep us more experienced flyers in new products (or any products at all). The new people need to be taught. Who's going to do it?? Are you teaching them??? I suggest you pick up a buddy box and teach these new people how to fly. But if you're not doing that then I suggest that you back off from attacking the instructors. This is the wrong forum to come into and bash instructors in, because most of the experienced people that frequent this forum ARE instructors that spend a large amount of time helping new people get started.


Ken

RE: engine tuning - pinch test
 

RCKen,

Other than the ocean of verbal diarrhea that you are spewing forth, you seem to take umbrage to the possibility that perhaps you too are clueless. I leave that determination to you and your hapless students. I have instructed hundreds of students over the course of the years, and have been appalled and dismayed over the general low level of knowledge and ability of the average instructor.

RE: engine tuning - pinch test
 

Excuse me now, I have to go cook an engine.:D

RE: engine tuning - pinch test
 

Gentlemen, lets keep this on topic and civil.

Please resist the urge to curse, flame, degrade, insult or embarrass someone in your post.

RE: engine tuning - pinch test
 

I do the pinch test to get a good 'ball park' setting for the highspeed needle. I then pick up the plane and point it straight up and verify. I do this before my first flight.

After that, each subsequent flight, I give the line a quick pinch to make sure I didnt bump the needle/it didnt move. You can get a feel for the RPM change and what it will sound like and its fairly easy to repeat the line pinch test accurately.

You should very rarely have to ever change your lowspeed needle once you have it set at a good setting.

RE: engine tuning - pinch test
 

So when I think my engine is fairly well tuned what am I looking for when I lift the plane and point the nose vertical? What throttle setting should I be at and how long should I hold it there?

RE: engine tuning - pinch test
 

Going along with "Piper Chuck", I rarely do a high end pinch but if I do, what I said is how i do it but I don't even think I have done it in a year. What I have seen is those who use it set the high end and then pinch test it to get every single leaning rpm out of that sucker and I just don;t agree with it. Honestly here, anybody can set a high end needle. it's the low end you need to get good at.

RE: engine tuning - pinch test
 

Your looking for a bit of an increase in rpms when you point it up and to make sure the engine does not sag. This does not guaruntee a flawless flight because if the low end is not properly set. Bringing the high and low together can be a pain but if you learn it right, It's a no brainer.

RE: engine tuning - pinch test
 

Yup, that's exactly what I do, at full throttle. It should increase a bit and not sag. Make sure to hold it up there for a good 5 to 10 seconds, merely pointing it at the sky and lowering immediately won't confirm the engine will keep pulling when you're taking off, or doing something vertical like a nice big loop.

RE: engine tuning - pinch test
 

These tests you are doing. Do they cover all nitro power engines??? (planes,cars,boats)

RE: engine tuning - pinch test
 

Well most airplanes at least to include fourstrokes. I don't pinch test them but hold em up to check it. Not sure about those RCV or RTV whatever they are. Most most airplane glow engines . Some these plane guys are car pros too, they may answer you

RE: engine tuning - pinch test
 

I don't run cars, so can't answer there. I can say they definitely do not cover boats. The ONLY way to confirm a boat engine (assuming it's driving a traditional boat prop as opposed to a plane engine on an airboat), has the right needle setting is to put it in the water and see how it runs. Boat engines should NEVER be run at high RPMs on the shore to try to tune them. Doing so is very likely to throw a rod.

RE: engine tuning - pinch test
 

Yea thats what I thought.

Thanks