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Post  rsv1cox on Sun Mar 17, 2019 8:07 am

Sorry for the painful descriptor gents but it's the best I could come up with to describe what happens to the fuel pickup tube in the vented 5cc tanked Cox Mercedes tether car.

Every single one of these that I have disassembled have had the pickup tube shortened and I have wondered why.  Usually it's a quarter inch or so....

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I try to keep all of these as original as possible and I go to great lengths to save as much as I can including gaskets and star reeds.  I clean the shortened pickup tubes and coiled wires and reinstall.

But this one went a little to far.  Some employee snipped the tube a little to short for my comfort zone.

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So I replaced it.

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But when I went to combine the back plate with the tank I found out why these were snipped.  The tubes in the vented 5cc tank peculiar to the Cox Mercedes does not provide enough space for the extended tube to allow the lower left case screw to pass through to the case because the venturi tube pushes it over.  

So, I shortened the tube and it went back together.  

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These wire coils provide two functions, they keep the tube from kinking and shutting off fuel flow and have an added benefit of filtering the fuel.
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Post  Marleysky on Sun Mar 17, 2019 1:15 pm

Bob, Excellent documentary of a painful procedure!  The reason for the short-snip on the fuel tube makes sense. The spring usage has been mentioned on another forum and the main believed reason for the spring was to provide fuel feed via callipry action up to the tube. So, If the tube doesn’t extend to the very bottom of the tank, the fuel will flow up the spring into the feed tube. Filtering  the fuel is a benifical side effect as is the anti-kinking in the curve. You’ll notice the spring usually extends past the end of the tube and ends in the area of the “last drop” of fuel depending on engine application. I think Paul G did a “how to make “ a aluminum tube and fuel tube to fuel nipple to eliminate the restriction of the spring for mouse racing. Roddie did a photo set of putting an aluminum collar on the fuel tube over the fuel nipple to prevent air getting sucked in as the fuel level drops below the nipple level.

Geeze, that was a lot of typing just to say the spring has a third use!!  lol!


Here’s a picture of Paul G racing set up:
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Post  rsv1cox on Sun Mar 17, 2019 1:51 pm

Thanks Rene, I missed that.

Another peculiar thing about these is that the pickup tube is always positioned toward the bottom of the tank rather than the outside despite being a tether car. There just isn't as much room in a vented 5cc tank as there is in an 8cc and those vents get in the way.

Capillary action, maybe. I have found engines that had been ran without the spring. Got to pull one and see for myself. But, these seem to leave an abnormal amount of unused fuel in the tank.

Bob
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Post  aspeed on Sun Mar 17, 2019 4:35 pm

I never heard of the filtering or capillary action thing.  I heard it was to prevent kinks and air bubbles.  We always took the spring out and directed it to below centre, and the Golden Bees to the centre for inverted flight.  Oh yes Paul used to race the Meese way back when we were young.  Can't remember who won, it was so long ago, probably Centralia in the 70's?  I guess he probably won, or tried harder anyway.
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Post  Mark Boesen on Sun Mar 17, 2019 8:51 pm

Remember Rusty did a video (?) on the capillary action of the spring? It was pretty amazing how well it pulled fuel up into the top of tube, yes they'll start without it, but i do think it helps getting fuel to the needle quicker.
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