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Check Valve on Fuel Supply Line


John76
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I've been testing a check valve on the fuel line to see if it keeps the fuel filter full and makes "hot starts" easier.

Results: Good so far.  Haven't had a really hot day in the last few weeks, so results may change.

Fuel filter stays almost full after a brisk drive and a 2-week sit. Starts right up without the need for excessive cranking to refill the float bowl.

Picture of the filter is after a 12-day sit.  The check valve (picture 2) needed a slight modification...replacement of the spring and plastic flap with a steel ball bearing.

 

Fuel Filter Full.jpg

Check Valve.jpg

 

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I had a bad experience with the same type of one-way valve.  However, I did not replace the flap with a ball bearing like you did.  I'm guessing that might make it work just fine.

 

When I first put the valve on near the tank like you did, it seemed to do the job very well.  But then after a few weeks, it would starve the carb for fuel.  Happened three times while driving and three strikes and your out.  Never had the starvation problem after removing it. 

 

I would certainly try the ball bearing modification but I don't need it any more.   I installed an auxiliary electric pump near the tank that I just use via push button to fill the carburetor.  I think your ball bearing mod is a great idea.   

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6 minutes ago, Dick R said:

But then after a few weeks, it would starve the carb for fuel. 

Dick,

Did you check the flap after you removed it? My guess is that it was melted and deformed, thus blocking the flow. I took one look at that plastic flap and thought it would never last long in the nasty fuel we get. I also compared the "suck strength" of 7 of these valves, and found they varied greatly! I tossed the flap and wimpy spring and just popped a 1/4" (6mm) ball bearing into the cage.

Hardly any resistance on the "suck test", and the valve is shut tight when the flow stops. Since no spring, the valve need to be tilted upwards slightly, so gravity lets the ball drop as needed. 

John

PS: Electric primer pump with push-button is a great idea. Where did you put the button?

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1.  I did check the flap.  It appeared to be made of some kind of rubber because it was flexible and I don't recall there being a spring, just the rubber flap.  It did not look deformed.  After my experience, I didn't want to bother with it any further.  And I wasn't clever enough to think of using a ball bearing. 

2.  I mounted the push button just below the choke knob.  Picture below.  Pretty much invisible from normal sitting position.  You'd have to know where it was to push the button.  It's a small button switch that closes the circuit only while it's being pushed. 

IMG_3772.jpg

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30 minutes ago, TobyB said:

You know, the mechanical pump has a valve built into it for just that sort of thing...

 

;)

 

channeling Tom.

 

t

 

Yup if the gas is draining back to the tank you have a air leak somewhere in the system, it's the old finger over the straw trick.

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22 minutes ago, TobyB said:

the mechanical pump has a valve built into it for just that sort of thing...

 

Yes it does, but it only holds the fuel from the carb to the pump. It's a long way from the pump to the tank, and any hint of an air leak will empty that line. So far, the check valve keeps fuel in the filter (before the pump)...and that has never been the case.

John

 

PS: This works for the mechanical "sucker" pump. An electric (pusher) pump would clearly solve the problem.

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True, but with the carb gas boiled off, and the float dropped, wouldn't the fuel in the line between the carb and the pump also boil off? If there is no fuel in that line, how effective is the one-way valve in the pump? If it leaks, then the whole line is drained all the way back to the tank, requiring considerable cranking to fill everything again.

John

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55 minutes ago, TobyB said:

You know, the mechanical pump has a valve built into it for just that sort of thing...

 

;)

 

channeling Tom.

 

Yes, I've typed out my experiences a few times now.  I'm glad someone remembers.   

 

It gets embarrassing, repeating myself. 

 

Searching "Stubby fuel pump" brings up 27 posts I've made.

 

https://www.bmw2002faq.com/search/?q=stubby fuel pump&updated_after=any&sortby=relevancy

 

Tom

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