Triumphrat

brittour95

I'm not the sharpest knife in the drawer, but I know what the 'on' position is for, and I know what the 'res' position means - I just don't have a clue what 'prime' is for. Somebody, help me!

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I warn you now, the velocity I'm gathering...

sco

The prime position is for filling the carbs up when they
have been drained eg carbs off the bike etc
when the bikes running it uses a vacuum method
to drag fuel from the tank
Sco

RacingGreen

On a vacuum activated fuel system, there is a rubber diaphragm in the petcock to control fuel supply. To avoid the tank above spilling fuel into the carbs and flooding them and the cylinders when the engine is off, a spring holds the diaphragm closed. When the engine runs, a vacuum is created by the pistons' downstroke. A vacuum line from the manifold (usually cyl #2) to the petcock is depressurised and pulls the diaphragm open - therefore allows fuel to flow to the carbs.

So - prime is used to fill the carb bowls with fuel when the engine is not running. That may be useful after a carb stripdown or - in my case when out of gas! :wink:

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Racing Green (what other colour should a Brit Bike be)?

RacingGreen

OK- I took so bloody long writing my response that Sco beat me to it.

Concise and to the point - good job, mate.

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Racing Green (what other colour should a Brit Bike be)?

That position is only to be used for a few moments. If you leave it on Prime it will eventually drain the tank through the carbs and if you havent' noticed that the fuel is dripping - think what could happen when you start the bike and the motor gets hot.

That position is only to be used for a few moments. If you leave it on Prime it will eventually drain the tank through the carbs and if you havent' noticed that the fuel is dripping - think what could happen when you start the bike and the motor gets hot.