To prime or not to Prime ?

[spooky]

Well this is the first time i have had a petrol tap with a prime position... yes really... so what is it for and what position do I    a?)   run it in and b) which position when stopped ie overnight..    also an interesting thing  is that you have to take the tank off to change the spark plug !! not really interesting cos it`s a pain in the  ****** (enter suitable word) stupid idea as speedo has to be disconnected and speedo wiring unplugged, so when it`s unplugged you can`t check if it`s got a spark .. 

[iansoady]

I think (but may well be wrong) that these are usually fitted where the tap "on" position is vacuum controlled by inlet depression. So if the carb is empty you'll be turning it over for ages till enough petrol comes through - so the prime position is for initial filling.

I hate those vacuum taps anyway. All that complication to save the bother of turning a tap off. In fact I converted the one on my 400/4 to be a conventional tap (the real problem as always was elsewhere).

[Steve Lake]

Ian is correct, and by strange coincidence i have the tap off one of my SRX's in my hand (it leaks... so need to order a seal kit). the prime position is used to run fuel directly to the float bowl when starting, as the main and reserve positions are only opened once the engine is running as they are opened by vacuum. as Ian says... a very complicated (and unreliable in my experience on SRX's)way of getting the go juice into the engine.

[spooky]

So best to leave tap in `on` position and only use prime if it runs out of fuel or hasn`t been used for some time ? then when it starts turn back to `on`       thanks   

[themoudie]

Aye Rufus,

Concensus! 

With Sally SRX and the Mono SRX, they both use this type of fuel tap, I always turn to 'Prime' before adjusting choke and then either priming the cylinder, with the kickstart or thumbing the starter button. As I have clear fuel filters, you can see the fuel flow into the system, this doesn't happen if the tap is in the 'On' position, until the engine is turned over. Once the engine fires up, just turn the tap to 'On' and it'll be fine for the rest of the day. When it is stopped, overnight or for any length of time, leave it in the 'On' position.

Happy trundling come the time. 

My regards, Bill

[spooky]

Left it on `on` all night, this morning pulled choke out, turned to prime, it started instantly , turned tap back to on and it was fine,     I am considering fitting a normal gravity tap, i have a spare gn one that looks like it will be the same size, but will give it a few miles to see how i get on with the stupid vacuum one, seems like a lot to remember !!!