Carburetor Problems!!

[magoconnor]

Hello Everyone. 

I'm having problems with my phbg type carburetor, it's installed in a kymco super 8 72cc ( with a polini open airfilter )
 

it's currently running pig 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 not able 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).     

What do you guys think? Maybe the idle jet? Please help me out. 

SETUP
Gy6 72cc
Manual fuel system
Open air filter. 

[jeff84]

what size idle jet are you using and how many turns out is the a/f ratio screw? if it isn't turned too far out you may be able to get the same effect by turning out a bit more as you would with a size bigger jet.

[pinkscoot]

What does your plug look like? Do you have a temperature gauge?

[magoconnor]

Hello.

The spark plug is deadblack.
The idle jet the size is unknown.
choker size 60.
it's about a quarter turn out, so not much.

Do you think it's the idle?

[magoconnor]

No right now I dont have a temperature gauge.

[magoconnor]

I have tried bigger main jets, but it just gets worse.

[jeff84]

actually if you are only running it 1/2 turn out I would be inclined to go with a smaller idle jet. if you can turn it all the way in without killing the engine or at least make it stumble to the point it sounds like its about to stall, then you for sure need a smaller idle jet. I am assuming that on your carb in is leaner and out is richer.


I was always told that if your idle circuit isn't dialed in then main circuit tuning is just an exercise in futility.

[magoconnor]

Ok thanks for the advise.

What do you think the idle jetsize should be?

[jeff84]

I would need to know what size you have now to answer that question. all I can say is smaller

[magoconnor]

that's the thing it does not have a number or anything.
Do you know the standard size?

[magoconnor]

For a 72cc with racing camshaft.

[jeff84]

I would say 38. but for all I know 38 is what you have and you need a 35. or maybe you have a 40 and yo need a 38. if that is the case 35  might be too small. there are kits that have a variety of sizes.


edited, because oops

[FrankenMech]

Do you have a leaking vacuum operated fuel petcock? Check your vacuum line at the intake manifold and see if there is gas in it.

A leaking float needle, saturated or sunken float, or high float level, will also cause excessive fuel delivery.