Fuel Pump gravity fed or suction query

richardh · Post by **richardh** » Mon Jul 18, 2011 5:37 pm

Hi, I've inherited an old classic with a top fed fuel tank (think its a replacement out of something) and the flat spots are horrid.
I've changed the distributor cap and rotor arm, checked the coil, leads and compression. All is good.
I put in a new filter (metal one) lower than tank and as near to tank as i could.
THen i removed the old pump and 2nd filter and put on this one from paddocks http://www.paddockspares.com/fuel-pump- ... ctric.html and it didn't run. put the old one that it was built with and it runs.
Dumb Question is: is this because my tank is top fed and the pump only pushes and not sucks/pushes or have i missed something?
I've checked the flow and the pump ticks and it was lower than bottom of tank, etc.
Stupidly, i'm stumped!

richardh · Post by **richardh** » Thu Aug 11, 2011 6:48 am

Someone must have an idea please

kiwicar · Post by **kiwicar** » Thu Aug 11, 2011 9:55 am

Hi
Those pumps can self prime to a height of about 4" above fuel level, however that is not gaurenteed and if they don't prime they burn themselves out in about 2 minutes, so it is best to always fit them below the tank.
Best regards
Mike

stevieturbo · Post by **stevieturbo** » Thu Aug 11, 2011 5:57 pm

below the tank, and gravity fed of course.

mgbv8 · Post by **mgbv8** » Thu Aug 11, 2011 8:37 pm

So the pump gets its feed from a dip tube coming from the top of the tank??

As Stevie says, the best way is a bottom / gravity outlet to the pump inlet.

Give us some pics of the tank connections and of course the classic car. What is it ???

Perry

richardh · Post by **richardh** » Mon Aug 15, 2011 8:24 pm

its a 1984 rangey v8
tank is an after market old one from somewhere. top fed, new inline filter and pump is below bottom of tank - so mimimal suck required to this point.

then new pipe runs along chassis and straight up into carb inlet.

I'm got the old pump still on so i can move it about but i've tried it vertical and side mounted.

Didn't have this trouble with a top fed one and same pump inside the engine bay in my converted series3 v8.

have tried pump on its own with a bucket of fuel and a long bit of pipe and that works..........

kiwicar · Post by **kiwicar** » Tue Aug 16, 2011 9:10 am

Hi
As the others have said feed the pump from the bottom of the tank, you are depenging on a good syphon and if the tank runs dry you will be over the 4", and as I said it takes very little running with a dry pump to burn one out.
Best regards
Mike

richardh · Post by **richardh** » Tue Aug 16, 2011 11:20 am

Thanks, I'll leave the old one on until the new tank and bodywork arrive and then do it all in one go as there's a lot of work involved.
Cheers folks

Ian Anderson · Post by **Ian Anderson** » Tue Aug 16, 2011 4:12 pm

NEVER build a tank with the exit on the bottom.

Manage to knock the fuel line off and you have an unstoppable flow.

With a syphon type system you can blow the air out the syphion and stop the fuel leaking.

I/m running a facit red top drawing fuel throuh a syphon type system in 8mm hose - no problems

With a GT40 from half tank down and when you brake the fuel sloshes forward and the pump sucks air (noise changes) 5 years of doing this and the pump still works fine!

Ian

kiwicar · Post by **kiwicar** » Wed Aug 17, 2011 8:32 am

"NEVER build a tank with the exit on the bottom."

That is unless you have fuel injection, a pump that is non self priming and prone to burn out or need to empty the tank fully

No if you need to take the feed from the bottom of the tank, but protect it if the underside of the tank is exposed.
Who on earth would leave the underside of the fuel tank so exposed that you could knock the bottom fitting off? ? ? That is just suicidal or in the case of the ford Pinto corperate manslaughter Oh yes that is who would design such a fuel tank . . . Ford!
Best regards
Mike

Ian Anderson · Post by **Ian Anderson** » Wed Aug 17, 2011 11:20 am

kiwicar wrote:"NEVER build a tank with the exit on the bottom."

That is unless you have fuel injection, a pump that is non self priming and prone to burn out or need to empty the tank fully
No if you need to take the feed from the bottom of the tank, but protect it if the underside of the tank is exposed.
Who on earth would leave the underside of the fuel tank so exposed that you could knock the bottom fitting off? ? ? That is just suicidal or in the case of the ford Pinto corperate manslaughter Oh yes that is who would design such a fuel tank . . . Ford!
Best regards
Mike

Oh yes Mike

But now most Efi Pumps are "in tank" and use the fuel to cool themselves - that to me also needs to be addressed - use a flamable fuel to cool a pump???????

Yes protect a bottom drain hole would work but trust me (i've done it) remove an inline fuel filter on a bottom drain tank and your stay there for an hour with your finger over the pipe till your brother comes out and finds the new filter that has disappeared under the other end of the car!

Top feed - blow the syphon back and no problem

Ian

kiwicar · Post by **kiwicar** » Wed Aug 17, 2011 12:21 pm

Hi Ian
" use a flamable fuel to cool a pump???????"

You have no sense of fun!

It works and (potentially) makes the tank less likely to explode as it will tend to over richen the air fuel mixture above the fuel in the tank and make it harder to ignite.
But I fully understand you feeling it is a bad idea. Understanding combustion and detonation is not as intuitive as I feel it should be

Best regrads
Mike

mgbv8 · Post by **mgbv8** » Wed Aug 17, 2011 7:19 pm

Ford made a dangerous fuel tank ???

stevieturbo · Post by **stevieturbo** » Wed Aug 17, 2011 8:51 pm

I think having an outlet for any efi pump anywhere than the bottom, is pretty daft.

As for fuel being dangerous ?? Not quite. Next you'll be saying it's crazy to have fuel surrounding the entire electric motor, brushes and windings....as it is in every single efi pump.

Petrol in itself isnt that dangerous or flammable. Petrol vapours are. Petrol vapours combined with "air" perhaps more dangerous. Add a spark and yes very dangerous.

But petrol in petrol tanks is actually pretty safe under nearly all circumstances.

kiwicar · Post by **kiwicar** » Thu Aug 18, 2011 10:43 am

You can quite safely stub cigeretts out in a puddle of petrol, done it loads of times. BUT the vapour in the right mixture is lethle and very easy to ignite, as I said it is not intuitive!
As regards the Pinto fuel tank the wikipedia entry on the pinto here http://en.wikipedia.org/wiki/Ford_Pinto mentions "alligations" about the design, these "allagations" led to the biggest fine for a corperate cover up at that time and a massive out of court settlement to families of owners toasted in Pintos.
Best regards
Mike