Vacuum fuel 'pump' and fuel system-possible to simplify?

[hillbillypolack]

I'm working on some minor mods to the M900 this winter.  One is the fueling.

With the unusual method of a vacuum operated fuel pump on the Ducs, is it possible to replace that system with a simpler (and traditional) petcock?  If for no other reason than getting fuel directly to the carbs at cold startup for quicker starts.

Thanks for any opinions, or pointers.

[Howie]

Yes.  Any 5/16 petcock will do.  How and where to mount it is up to you.  Unless your carbs are leaking or there is something wrong with your vacuum shut off starting will be the same.  If you want I can post a picture of mine.

[hillbillypolack]

That'd be fantastic.

The issue I have (and I think we all have it to some degree) is that when the bike has sit for some time, there's no gas in the line for the carb.  The engine cranks and cranks (at the expense of battery charge) until the carbs suck enough juice to get them started.

My hope is that getting around that ritual would be quicker for startup and easier on the starter and related systems (battery etc).

[He Man]

how long are you letting it sit? If you bypass the pump, the system would run until gravity can no Longer push the gas Down due to a low pressure.

I thought vacuum pumps are fairly common on carb vehicles.

[koko64]

There may be some confusion between vacuum operated petcocks and vacuum operated fuel pumps.
Piss off the vac operated petcock for a manual fuel tap, but keep the fuel pump. The fuel pump flows well, is rebuildable and lets you use more than half a tank of fuel at a time.

[Howie]

Here is the photo I promised.  The red dial is the petcock.  If you shop you can get a color you want.  My bike, as you can see, is no beauty queen, so...

[Pedro-bot]

So you left the vaccum pump bolted in place and rerouted the fuel lines to the petcock?

[Nomad]

You can throw out the vacuum petcock, and there is a fast way and a long way to replace it.

You replace the fuel line itself to the manual petcock, but there is another line running from the vacuum petcock.  The short version is, you seal it with a 5mm bolt or screw or whatever of your choice with some adhesive with your choice.

The long version is you follow that extra line back to your intakes and seal it there, which is a much more involved process, though you clean things up and it looks better in the long run.  I would vote for that if you have the time, though I've only got the short version done on mine.

Either way, get rid of the vacuum petcock, if it fails, your engine gets filled with fuel and is a royal pain in the ass, even if you don't break anything, which happened to me.

[hillbillypolack]

^
That's one of the reasons I was asking.  During the rebuild many years ago the petcock allowed gas to flow into the engine.  Thankfully it didn't start and a mechanic caught it before I did any damage.. 

HeMan-the bike has been on the service table almost all summer, so if there's a way to get gas flowing for initial startup, I could certainly use a pointer or two.

Thanks.

[Nomad]

That's easy, open up your air box, spray some starter fluid into your carb intakes, and hit the start button.  It might take a couple tries, but it will work much faster than cranking your starter again and again.

If you don't have starter fluid, you can use a couple drops of gas, not highly recommended though.  Keep your face away from the carbs when you hit start.

[He Man]

just run a manual petcock in line and leave it open until gravity fills up the carbs.

if you dont want to do that, then any solution is not worth the effort of just cranking it for about 30 seconds til lthe carbs have enough gas to start the bike.