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General Category >> Rubber Side Down! >> Stock Vac Petcock question
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Message started by PhantomII on 08/27/13 at 07:00:46

Title: Stock Vac Petcock question
Post by PhantomII on 08/27/13 at 07:00:46

Is the stock petcock some kind of fuel pump that works off the engines pulses? I have about 50 antique outboard motors mostly Evinrude and Johnson from the '50's and '60's some of them use a pressurized fuel tanks and the other have a engine mounted fuel pump, but all of them work off the engines pulses to pump the fuel, so is that what the petcock on our Savages do?

Title: Re: Stock Vac Petcock question
Post by Dave on 08/27/13 at 07:46:03

No....the petcock is not a pump.....it is a valve.

The engine vacuum pulls on a diaphragm and opens the valve that allows the fuel to flow by gravity. There is a tiny internal orifice that smooths out the pressure pulses of the engine intake and creates a smooth vacuum on the diaphragm.

When your float bowl is dry from storage....you use the PRIME function to open the valve and allow fuel to flow manually.

Title: Re: Stock Vac Petcock question
Post by PhantomII on 08/27/13 at 07:52:59

Thanks Dave, it just seems that they over engineered this fuel delivery system when a simple on and off valve would have sufficed.

Title: Re: Stock Vac Petcock question
Post by Dave on 08/27/13 at 08:52:41

It is an attempt to make this bike user friendly.....by being automatic instead of manual.

The problem is that the petcock can be problematic......and erratic. If it just flat stopped it would be an easy problem to identify. The problem is that the failure can cause a lot of confusing symptoms.