21mm Phbg

[magoconnor]

Hello.



I'm having some problems with my 21mm phbg carburetor, it's installed in a kymco super 8 72cc 4 stroke with open airfilter.



It has always been runing very rich, but i'm able to reach a reasonable highspeed with medium takeoff.

I have tried a world of main jets, coming all the way down from a 90 to 73 size.



it's not supper aggressive and bogs a little under full throttle. I can actually go faster at 50% throttle to 75%



If I go any lower in main jets, I'm unable to give it full throttle, but it's more aggressive but less top speed.



A funny thing accured, when I was just about to run out of gas, with the 73 main jet. It felt alot more powerfull and pulled better overall.



It smokes alittle when it idles (white).



The carburetor is setup, as I have come to find out for 2 stroke, while mine is a 4 stroke.

My main jet 73

Not sure about the neddle.

Atomizer au 262

Choker 60

Idle unkown



I hope you guys can help me out. .



Best Regards.

Magnus

[tsimi]

Is it a genuine Dellorto carb, like a black Stage6, or is it a Motoforce or other clone? If you don't know just tell us how much you paid for it.

Not much experience with 4 strokes but with 2 strokes with an open filter you would be somewhere in the 100-120 main jet range. Pilot jet, that's the small one between the main jet and choke jet(60) should be somewhere around 38-42

For example my 21mm has the following setup on a modified stock airbox.

Atomizer AU262
Needle W7
Main jet 95
Pilot jet 37
Choke jet 60
Slider #40

Mixture screw 1.75 turns out
Idling set to 1900-2100 rpms

Was just thinking...
If you haven't changed the pilot jet yet you might have a 50 or 52 inside which is a bit too big. The pilot jet affects the whole range of throttle from idle to WOT (wide open throttle)
Which means you could be running too rich on the pilot jet that is why you have to use a small main jet to compensate for it.

[tsimi]

Look at the post of Ryan in this topic. (7th post)
There you can see some charts and data which might help to understand the behavior of a PHBG better.

49ccscoot.proboards.com/thread/19303/phbg-uni-filter-jetting-baseline