Planet Minis

oilspot

Loads of threads on jetting, and yes I do have a specific question, but let me attack this question myself by first trying to make sure I understand how the pilot circuit works.

The size of the hole/holes on a pilot jet meter the amount of air that's allowed to mix with the fuel mostly when the throttle is closed or most of the way closed.
So a smaller hole (smaller pilot jet) means less air. Then you can fine tune via the air screw. Turn the screw out and it will introduce more air.

So does that mean that having the airscrew turned all the way in will cancel out most of the air entering that circuit?

CJsDad

The pilot jet is for idle to 1/4 throttle. If you turn the air screw all the way in and the motor keeps running, your pilot is too big.
The smaller the hole in the pilot means less fuel at idle and the start of the throttle movement. Giving you a lean condition. It is better to be too rich than lean on the pilot.
You can also replace the jet for the air screw on some carbs.

oilspot

So the hole in the pilot jet meters in the fuel... not the air.

So you turn the pilot screw all the way in, it stalls, your too rich because of the pilot jet. You further richen the mixture (choking the engine to death) by turning the air screw in and it stalls. confirmation of a rich pilot
... go to a smaller pilot

So lets say I go out and turn the screw all the way in... the bike continues to idle. The bikes already so leaned out that further starving it of air via the air screw doesn't kill it. So that would confirm a lean pilot.
...go to a fatter pilot


your bike runs crisp at and off idle
...leave the pilot alone


if this is a good train of though, good theory... let me know!


I'd much rather have a techinque/ theory going about tuning than randomly tossing jets at a carb!

dood

Winner!!!! Johnny tell the young man what he won....

josh302

rule of thumb is:

1.5 turns out starting point

if you go more than 2-2.5 out you need smaller pilot

less then 1 turn you need larger jet.


if it is too fat on pilot, it will run real stumbly idling around in 1st gear.

cmb

thanks for this post

oilspot

thanks for the feedback. Now I have a solid method selecting the correct pilot.