Super Jet Pop off - Whats right?

[Parsonsjb88]

Ok, so I'll start with yes, I've read basically every single carb tuning manual (Mikuni, Group K, Watcon, etc) like 10 times over, so I understand very well what pop-off is, how to adjust it, and have good idea of what my pop-off should be. However, my concern is that 99% of the resources I've found do not talk about "how" the pop-off should react. I've read multiple different opinions from "a clean pop-off dropping no more than a few psi" to "dropping 10-20 psi is ok" and even some people that say "its OK if it leaks slowly down to a hold point".

So, in an ideal situation if I was setting my pop-off to 36psi, what should happen once the needle pops at 36? Right now, one of my carbs is cleanly popping and re-seating at about 30 psi very consistently; while the other is popping more aggressively and re-seats cleanly between 14-18 psi.

 

[Vumad]

So, in an ideal situation if I was setting my pop-off to 36psi, what should happen once the needle pops at 36?

A good popoff should be like opening a well shaken can of coke. A bad pop-off is like a bottle of coke with a cap that isn't tight enough as you shake it so you hear air leaking. If the cap is tight and you hear air leaking, then you have a bad cap, or in this case, needle.

It doesn't matter how much the popoff drops when it pops. It matters how it pops. It should pop crisply and seal crisply with no leaking or bubbling. If it drops 5, 10 or 15 PSI when it pops is less important than how it seals afterwards. It should seal immediately with no dribbling or bubbling. It also doesn't matter if it seals at the same number every time, as long as it's within range of popping the same everytime.

 

[Parsonsjb88]

Sounds good. So even tho one of my carbs is popping off to a much lower number it should be fine since the popoff is the same and they seal cleanly (arent leaking or bubbling)?

 

[DAG]

No you must have the pop to happen at the same psi. It's typically better to slightly bend the arm than strech or cut springs to adjust them as equal as you can.

Pop clean (no bubbles prior to pop)

and seal clean (no bubbles after pop)

 

[Parsonsjb88]

No you must have the pop to happen at the same psi. It's typically better to slightly bend the arm than strech or cut springs to adjust them as equal as you can.

Pop clean (no bubbles prior to pop)

and seal clean (no bubbles after pop)

They are popping at the same PSI, 35PSI each. No leaking before or after. my concern is that one, after popping (no leaking) seats cleanly and quickly at about 17psi. The other pops at the same 35psi but reseals at like 30psi. No leaking either

 

[Sasquachcrap]

No you must have the pop to happen at the same psi. It's typically better to slightly bend the arm than strech or cut springs to adjust them as equal as you can.

Pop clean (no bubbles prior to pop)

and seal clean (no bubbles after pop)

....but. Be sure your re wetting the seat with some double d 40 between pops.

 

[Parsonsjb88]

Ya i am, every time. And they both do what I said very consistently (35 pop to 30 and 35 pop to 17). Think i should get some new needles and seat?

 

[smoofers]

Ya i am, every time. And they both do what I said very consistently (35 pop to 30 and 35 pop to 17). Think i should get some new needles and seat?

Sounds like you're good. After popping off the wetness is gone and consistency isn't guaranteed. A clean pop is what you are looking for and sound like you have it. If you adjust the arms to adjust pop off, just always make sure the needles still seal with the diaphragm and back plate installed. That and pressure test your carbs (10 psi for 10 minutes) to make sure your fuel pump side isn't leaking.

 

[jo5hi3]

....but. Be sure your re wetting the seat with some double d 40 between pops.

Double D 40.... Is that the name of your blow up doll??