WHAT'S THE PINCH TEST??
 

What's this pinch test i have been hearing alot about lately and how do you do it correctly. I've heard a few different ways of doing it and i want to find out which way is right.

Cheers

Not really sure, are you wanting to check for compression on your motor?

If you're referring to test the bottom end (low speed needle tuning), you pinch the fuel line while idle, and count how many seconds it takes for the engine to die out. If it dies immediately low end is too lean, if it doesn't effect the engine for a while, it's too rich. If the engine revs up and dies all within a 4-6 second range, you're close on getting a rough tune for bottom end.

stupid question, where do you pinch the tube, close to carb?

doesnt matter, wherever you can get your fingers to...

I am guessing you are wanting to test for compression.

-Remove the engine from the vehicle and leave the glowplug in and flywheel on - remove exhaust.
-Hold the engine by the flywheel (clutch close to you and exhaust port away from you - crankshaft level with the ground).
-Hold engine with the cooling head up.
-Let the cooling head tip to the side and gravity will try to make the cooling head rotate to the bottom. The pinch/compression will try to oppose gravity.
-If the engine has enough pinch/compression, it should hold the head up for at least 10-15 seconds before the gravity wins and the head rolls to the bottom. If it rolls over sooner, then the engine may start, but will probably flame out as the sleeve expends and compression is reduced.

This is not a very scientific test and results may vary, but it gives you something to go by...

It will matter as the farther from the carb, the more fuel is in the fuel line causing any reaction to be delayed. Try to pinch the line as close to the carb as you can.

Thank you, that is pretty helpful, so are we still looking for 4-6 seconds close to the carb then?

Yeah buddy that's the one i'm referring to, thanks. My motor picks up revs then dies within the 6 second range so i'm happy:D

Is there a similar type of test for the HSN?

Thanks jkas10 i will try the compression test aswell;)

i do this test with cooled engine head but it seems to vary between without and when i've put after run oil in it.
i would assume its best to do this test without the after run oil yet?

Remember that this test is just to get you in the rough ball park of tuning the LSN. For the HSN, just make sure you have good smoke at WOT, and the motor runs consistent. If the HSN is too lean, it'll be fast as hell at first, then start to loose power later in the tank, richen it up if this happens. Important thing to remember about tuning the HSN is to not tune it right away, but run it hard for about half a tank, and then start tuning it.

Yep, thanks RevMaxx - I do it with a cold engine and no after run oil as the oil will create a sort of seal between the piston and sleeve. thanks!