Testing pop off

[ATS_Aaron]

Is the pop-off pressure when the needle first pulls off the seat and barely starts to "leak" or is it when the spring collapses 100% and the needle is almost completely blown out of the seat, or is it some point in between?

Aaron

 

[marz831]

Make sure you lube the needle with some wd-40 so you get a clean POP. It will start to "leak" if it's dry.

 

[#ZERO]

Whatever pressure makes the needle and seat start to leak.

If you press the needle and seat open and spray some WD-40 inside, it will help to give more accurate readings.

If you see air bubbles or hear the needle and seat leaking before it burst open, replace it.

 

[Matt_E]

Yes, lube it with WD40, and it should pop open cleanly. Pump it up fast, that makes for a cleaner pop, too.

 

[ATS_Aaron]

Thanks for the tips. If I fill the area with some PB Blaster and run the pressure up fast I get a good POP about 14 psi. Mikuni book says I should be at 15 psi, so that's pretty close.

Thanks,

Aaron

 

[Shonuff]

Nice.

What I like to do is forget I have the carb pressurized and press the needle arm shooting WD-40 in my face and all over my safety glasses.

 

[5810]

:nutkick:Safety first

 

[Ericfox]

Nice.

What I like to do is forget I have the carb pressurized and press the needle arm shooting WD-40 in my face and all over my safety glasses.

Yeah... WD-40 in the eyes stings a little doesnt it... done it- and now I lay the cover plate back on the carb while pumping it up to test...

 

[Matt_E]

WD-40 in the eyes stings a little doesnt it

Not as bad as carb cleaner, or clear coat.

 

[Scraggly]

Not as bad as carb cleaner

no kidding, been in the hospital once for that one, not a pleasant experience

 

[Pablo]

I have the Mikuni manual and see the expected pop off pressures for different springs and needle combo's, but how do you determine what is desireable for each carb type (38 vs 44 vs 46...) and then when you throw in A/M flame arrestors that necessitate lowering you pop off it sends me spinning? I realize that carb tuning is more of an art than an exact science but I need some solid foundation to get a handle on it.

 

[Waternut]

I have the Mikuni manual and see the expected pop off pressures for different springs and needle combo's, but how do you determine what is desireable for each carb type (38 vs 44 vs 46...) and then when you throw in A/M flame arrestors that necessitate lowering you pop off it sends me spinning? I realize that carb tuning is more of an art than an exact science but I need some solid foundation to get a handle on it.

I think you're digging too deep man. If there was a desireable pop off pressure for each carb, there wouldn't be an adjustment for it in the first place. It has more to do with your engine, flame arrestors, pipe, etc. (aka total setup). It's just like jetting. You can counter a higher pop off with a larger jet and a small jet with a lower pop off so if your engine runs clean from idle to 1/4-1/3 throttle, you've found the right combination. I'm sure there is a science to it but it'd be way more math than even I'm prepared to do. This is one of those things where trial and error really is the best method.