Left the petcock in the \"on\" position

I was in a hurry to get into work tonight, i had 1 minute to punch in and yes i made itB) In the process i forgot to turn the petcock tot he off possition. Would this hurt anything? When i came out frome work 4 hours later, she started right up, and there were no strange noises and it rode great home.

Nope. Won't hurt a thing. Some guys turn theirs off to lessen chance gas won't over-power the float needle in fuel bowl. This shouldn't happen if everything is right anyway, but it's just a precaution.

racer54 wrote:

Nope. Won't hurt a thing. Some guys turn theirs off to lessen chance gas won't over-power the float needle in fuel bowl. This shouldn't happen if everything is right anyway, but it's just a precaution.

I agree. And here's some blow-by-blow.

Fuel flows into the float bowl by passing through a hole in the float needle seat and around the pointed tip of the float needle.

As fuel level rises in the float bowl, the float rises and pushes the pointed tip of the float needle into the hole in the float needle seat. With a good fit between the needle and seat, and no grit or crud interfering, the needle tip completely plugs the hole whereby no more fuel is allowed to pass through the hole into the float bowl.

Absent a perfect fit between the float needle and seat orifice (damaged or worn out needle tip and/or seat orfice, or grit/crud interferance), or other reason such as incorrectly adjusted float level, fuel may just keep right on flowing into the float bowl.

Carbs having a properly functioning float bowl overflow will allow excess fuel being allowed into the bowl (via incomplete closure of the needle/seat interface) to escape from the bowl through the overflow nipple (usually dripping out through tubes running from the nipple to underneath the bike).

To guard against a float bowl overflow condition from whatever cause, a properly functioning petcock in turned off position will prevent fuel from reaching the carb. This precaution addresses the symptom, and is a good practice IMO, but does not cure the underlying problem of leakage (imperfect sealing) at the float needle/seat interface.

A small leakage may not significantly impair operating performance as the engine is consuming enough fuel to overcome it. But where fuel level rises to the overflow level, it has by definition exceeded the correct service level, and probably causing an over-rich mixture.

Some carbs such as smoothbores don't have overflows. So extra diligence is required toward the float needle/seat interface.

Excess fuel into the float bowl not allowed to escape through an overflow often goes on up into the carb throat and from there (1) into pods or airbox (where it can flow directly into the crankcase via the crankcase vent hose) and (2) into the combustion chamber and around piston into crankcase. Such fuel intrusion into the crankcase can happen regardless of whether the engine is running.

The "best" precaution IMO is a properly functioning float needle/seat interface being operated by a properly functioning float at a properly adjusted float level.

With a perfect fit at the float needle/seat interface being so critical, it is important to keep the same float needle with the same seat (i.e., do not mix and match). This is why they are usually sold -- and should be replaced -- as a matched pair.

With my 29's and stock airbox, the stock s-shaped formed hose from crankcase vent into airbox is removed and replaced with a long hose fitted to the vent and routed underneath the bike.

Kind thoughts and ride safe.

Does this mean all the guys here who have "fixed" their leaking carbs by replacing the petcock were wrong?
Yep!