scooter popping noise By millsc (Read 10,622 times)

[millsc]

my scooter will pop when i let off the throttle about 1/4 throttle, it popped with the 18mm carb also i tried to turned the a/f screw out a half turn still pops but not as bad, strange thing is that it was colder yesterday and no popping but today was warmer and the popping started again my valves are set at .003 intake and .004 exhaust btw i changed the head to hoca head and a 52mm bbk it popped when the ebay kit was on too only thing that is the same is the exhaust pipe

[Alleyoop]

Your LEAN bro, Could just be your idle is set to low and allowing the butterfly to close to much when you let go of the throttle closeing to many of the tiny holes by butterfly.

POPPING GETTING on the THROTTLE = RICH
POPPING LETTING off the THROTTLE=LEAN
Alleyoop

[millsc]

so my idle jet is lean? My idle is set around 1500 china tach so turn the a/f screw out to three turns?

[Alleyoop]

Sure, or idle it up a little more just as long as your rear wheel is not spinning.

[millsc]

i just checked when i turn the throttle back slower it doesn't pop i usually twist it back fast

[Alleyoop]

Yep when butterfly is close all of a sudden you just cut off the fuel and it will run LEAN.
That is why they have ACV valves on most of the CVK carbs to stop it from running lean when the throttle is suddenly closed. The ACV valve by default is allowing extra air to pass through that is one reason it is sometimes a little harder to adjust the AIR FUEL MIXTURE because your also working against the ACV valve. With the sudden closer more vacuum is created and opens the valve and sucks in some gas to richen it.
Alleyoop

[millsc]

it runs best at 2 turns out so just leave it i guess and not slam the throttle shut?

[Alleyoop]

Raise the idle some that will leave the butterfly a little more open but won't effect your fuel screw setting.

[looker]

I always had this problem on my scoot, changed carb, intake manifold, vacuum lines, even the exhaust manifold gasket.
Nothing stopped the popping/farting 'til I removed the P.A.I.R system.
Now it's gone, so has the popping.

[terrilee]

also try replacing the plug with a NGK

[millsc]

took it for a ride at three turns out idle turned up to about 1800k still pops every so often would lowering the needle help any?

[millsc]

or just get a 38 pilot?

[Alleyoop]

lowering the needle your Leaning it out WHICH is causeing the POPS if anything you would RAISE the needle to allow more fuel.
Sure you can try the #38.
Alleyoop

[millsc]

i meant raise the clip

[Alleyoop]

NO, Lowering the Clip RICHENs it(raises the needle--more fuel), Raising the Clip LEANS it( drops the needle--less fuel).
Alleyoop