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SU carbs lose fuel prime when not running

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Martinld123

Martinld123

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Is it normal for my 100BN2 1 3/4" SU carbs to drain petrol down when off for period of time? If I restart within short period of time the fuel pump does not come on until engine is running but if engine is off for say hour pump comes on when I turn on key. Does this mean I have fuel leak? Thanks Marty
 
In the case of a brief shutdown and then a restart, the fuel pump will not come on if the float bows are full and have closed the float valves and the fuel lines are full from the tank. In other words there is no place for the fuel to go so pressure at the pump is instantly high enough to shut it off when you turn on the ignition. As soon as the engine starts ( and that's the important part) the float level drops and the pump will kick on. Perfectly normal. My guess is that over a longer period of time, fuel leaks back through the fuel lines to the tank so when you turn the ignition on after a longer rest, the pump kicks in. You should note that if you don't hit the start button the pump will shut itself off in 10 or 15 seconds, after it has pushed fuel back into the lines.
 
Hi Marty , I agree with Roscoe on this one . My BJ8 works exactly the same way . Before I start mine , in most cases , I like the fact that I hear the pump going through a cycle and from the sound of it shutting itself off , the pressure switch is working and the float needles are seating correctly . Sounds like yours working great so enjoy the ride .
Hope this helped ,
BobbyR
 
If, after an hour, the fuel pump only clicks a couple of times, that's normal. If it clicks for a few seconds, then you may have a leak, which my be back into the tank.
 
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