Crabby

I am new to nitro racing, and i am still tuning my needles. Do i have to pinch the fuel line strong or lightly? I pinched mine lightly and it quitted in 9 secs. (I am still in break in)

Maximo

iTrader: (11)

If I were you I would not bother with the pinch test, its not overly accurate and will usually end up causing more confusion and trouble then anything else...IMO its one of the stupidest tuning ideas I have ever heard ! and if someone ever advises you to be pinching the fuel line to check tune I would completely ignore any of their tuning advice

Listen to the engines idle speed... that will tell you if your LSN mixture is correct..a proper LSN will allow the engine idle nice, slow and relaxed with a very slight miss..If your idle is fast, steady and sounding like a box of angry bees it means your mixture is likely too lean, or you have the idle gap too large.........In the end there is no better way to check the LSN mixture then to listen to the engines idle characteristics...Pinching the fuel line is just plain stupid !

Zerodefect

https://www.youtube.com/watch?v=iwzcWLKKU0I
Still the best explanation.

jkas10

iTrader: (123)

LOL at Neal (Maximo). Seriously, I am. LOL!

Maximo

iTrader: (11)

Yep..whenever I see guys doing the pinch test I know right away they don't what the hell they are doing !

Maximo

iTrader: (11)

The issue with the pinch test is that its not consistent.. So many factors will play a role in how long the engine takes to stall...Air temp, Air density, fuel type, glowplug type, engine type, engine condition, glowplug condition, where on the line you pinch, bearing drag, idle gap size etc etc..Because of all these factors involved its really impossible to get any real tuning data from pinching the fuel line....Far more accurate to simply adjust the idle mixture and listen to how the engine idles...a Lean LSN will cause a fast angry idle, and a rich LSn won't even idle....... If you tune to have a nice slow and relaxed idle you know for sure your LSN mixture is correct ! The best time to check the idle mixture is after a qualifier when the engine is fully heat soaked... Have your pitman leave the car on pitlane idling and if the LSN mixture is correct the engine will still be idling when you come down off the drivers stand....

Many times I have seen guys with absolutely perfect tunes sitting there messing with their needles because of the stupid pinch test ! frustrates me to no end and is one of the reasons so many guys struggle to tune these engines.

Frank L

iTrader: (148)

To answer your original question...

QUALIFER: The pinch test is designed to let you know if your lsn is in the ball park. It's not an end all final say type of test. It's another tool and I, a big fan or more tools...

Let's say you are having issues with idle and power. Your engine seems ok but something is off. If you do the pinch test and the idle raises at 3 your LSN is too lean. If it does not raise until 12 you are very rich on the LSN. I usually tune 4-5 buddy's engines when Im at the track. I'm no Dyno Dan but the smile on the racers face when his engine does not flame out, makes great power and sounds awesome is enough for me. FYI a bench tune from Dyno is 99.9999% dead on, I have never seen another do it.

timjs

I agree that the pinch will tell you if you're wayyyy off the mark. Specifically, if it's rich as hell. However, if the pinch test result is anything other than way too long, I disregard it totally. A wider idle gap will burn off the "pinch test" faster.