Fuel line pinch test for needle valve adjust - how to?
11-01-2003, 01:10 AM
#1
Fuel line pinch test for needle valve adjust - how to?
I read how to do this a few weeks back and I thought it sounded backwards. Could someone who is sure of the right way explain it to me?
1) I thought if you pinch it at full throttle and it wants to quit after you pinch it, that is lean (makes sense, not enough fuel, it dies).
2) If it speeds up right after you pinch it, it's rich?
3) If it speeds up slowly it's just right?
Thanks,
Joe
1) I thought if you pinch it at full throttle and it wants to quit after you pinch it, that is lean (makes sense, not enough fuel, it dies).
2) If it speeds up right after you pinch it, it's rich?
3) If it speeds up slowly it's just right?
Thanks,
Joe
11-01-2003, 01:15 AM
#2
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RE: Fuel line pinch test for needle valve adjust - how to?
It should speed up momentarily, then will die if you don't release it.
If it speeds up really slowly, it's either still too rich, or you're not pinching it enough.
If it instantly dies, instead of speeding up a bit first... it's too lean.
It's just a quick rule of thumb kind of check though... not rocket science.
Pinch it... listen for a slight increase in rpm before it leans and tries to die out.
If it speeds up really slowly, it's either still too rich, or you're not pinching it enough.
If it instantly dies, instead of speeding up a bit first... it's too lean.
It's just a quick rule of thumb kind of check though... not rocket science.
Pinch it... listen for a slight increase in rpm before it leans and tries to die out.
11-01-2003, 12:28 PM
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RE: Fuel line pinch test for needle valve adjust - how to?
Joe, you've got it right. That said, the pinch test is just a quick and dirty method of getting your n.v. in the right neighborhood. The final test is the nose-up setting. When you think you have the n.v. where it ought to be, then lift your plane, preferably with a helper on the throttle stick, and hold the nose straight up. When you go nose up, the engine should lean out a bit more than when held level with the ground, but still run strong. If it starts to sag off, you need to open a click or two, then try again. Ideally you should do this test with just a couple ounces of fuel in the tank. If your engine can suck fuel from the bottom of the tank and run strong without sagging, then you can fly with confidence that you will not flame out. Not a bad idea to do this at the start of every flying session.
Further on the pinch test: normally I pinch real tight for maybe a full second, then release. If the setting is rich, a short pinch will tell you pretty quick and the engine will speed up very audibly, no mistake about it. If it dies or wants to die, you're definitely too lean. If not much happens, you're close enough to do the nose up test.
On occasion I've had engines that test OK with the pinch and the nose up, but then flame out after just a minute or so in the air. When that happens, I usually find a change of glow plug to a hotter plug will solve the problem.
Further on the pinch test: normally I pinch real tight for maybe a full second, then release. If the setting is rich, a short pinch will tell you pretty quick and the engine will speed up very audibly, no mistake about it. If it dies or wants to die, you're definitely too lean. If not much happens, you're close enough to do the nose up test.
On occasion I've had engines that test OK with the pinch and the nose up, but then flame out after just a minute or so in the air. When that happens, I usually find a change of glow plug to a hotter plug will solve the problem.
