What is the Pilot Jet Plug for?

[Guest]

I have been reading about my carbs and how they work. I cannot understand why there is a rubber plug covering the Pilot Jet. How can it work if it is plugged up.

Any incite would be appreciated.

[chuck hahn]

Because it doesnt drink gas directly from the bowls like VM carbs do. It drinks thru the pilot circuit inside the body.

If its not plugged the idle cicuit is flooded with raw fuel and it wont run...well not ver well anyway.

[Steve]

Close, Chuck, but not quite.

The pilot circuit actuall gets it fuel from the main jet through a diagonal passage between the two. At low throttle openings, when the pilot circuit is active, there is no restriction imposed by the main jet, so the pilot can pull all it needs. As the throttle is opened farther, the needle circuit starts feeding more fuel. Guess what? It draws its fuel through the main jet, too. By the time the main jet is called into full play, there is not enough fuel being pulled through the pilot circuit to matter, so very little fuel goes through there. However, if that rubber plug were not there, the needle jet could get even more fuel because of the additional open passage.

This diagram from the factory service manual shows it quite well.
The rubber plug was colored for a previous explaination, I have never bothered to change it back to black because it just works so well.



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