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Excessive Fuel pump pressure? ….solved


Unkel Kunkel

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Spitfire Mk1V..

Engine burst into life today after many years of slumber..

A sort of, “ It lives, Igor! , it Lives !”, moment 

But petrol pouring out of both SUs

carbs have been overhauled -  new floats and needle valves.

Stopped  and blew out valves in case of “ debris” /rubber slivvers  etc affecting needle valves = same.

Found an ancient “Command” gauge - checked fuel pump pressure  = approx. 7psi.

31F21B31-23DE-450C-B3EF-1C33BE085D1D.thumb.jpeg.524c6e166ae424deb442d2357a32148c.jpeg

Isn’t this a bit high ? 

The pump is new ( Powertune from J Paddocks)

pressure regulator needed?

Return it - but wonder if  they all like this now?

So Considering -regulator
Take the spring out of the old one?

Appreciate your views and advice

 

Andrew


 

 

 

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1 hour ago, Pete Lewis said:

exactly which pump  do you have a plastic  insulator or not 

 mkIV should have no spacer and short arm pump 

as mix and no match can attribute to too high or too low pressures depends on the pump arm and spacer or not 

Pete 

 

Hi Pete ,

The original pump is as fitted in  1973 - no spacer , straight,  short lever one like this: C32B995A-9125-449A-83B7-4595F7DF64B9.thumb.jpeg.90b54c1c8be01367bf5f90b9a5bdeebb.jpeg

The replacement is this :

7C3EC3AD-0C6D-4989-BF9A-168C7D32BDE8.thumb.jpeg.a025628e3b67820e8373ac2b913edf4c.jpeg

which is listed on the receipt also as RKC1624.

It terms of the arm it looks just the same size and angle.

No spacer, just a paper gasket.It went on easily.

 

The manual suggests adding paper gaskets to reduce pressure.

The pressure would seem to be determined by the spring under the diaphragm which as the pump lever comes off the heel of the cam the spring is free to return the diaphragm upwards and pump outwards.

So it would  seem spacing , by limiting the travel of the diaphragm downwards would also reduce the “return stroke volume” that the spring is able to deliver - so the volume - and pressure would be lower.

Return it - or are they all like this.

Pressure regulator .

Canabalise the old one for the  main spring?

I appreciate your views and advice 

 

Andrew

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many have used the old spring if its able to swap without wrecking it 

ans yes spacing would reduce the pull on the spring but thats going to take a lot of faffing about with a trial and error to get a result 

its really just blasted annoying this stuff is made with no respect for the basic specification 

i cant think of any carb that has ever been designed to work with 7psi  its just  nuts 

a regulator would solve it but why should we have too ???

its just not fit for purpose  then where else do you go JP are generally reputable 

its ying yong foo junk we are plagued with    

a number of electric units do specify the output pressure/volume so you have some idea of what you are getting 

but the old spring is the simplest solution if thats the way you wish to go 

Pete

 

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Thanks everyone.

I will inform Paddocks and see how they respond.

I should say I have used them for years and hold them in high regard.At the very least they need to  be made aware there may be issues at least on some pumps regarding pressure being twice the upper  specified limit.

However, I suspect that they all have a similar problem.To preserve their good name they may have  take it up with their suppliers.

Maybe these things are just too cheap..

Out of curiosity, I’ll take the spring out of the old pump and compare it Depending on response from JP may swap it over.

In any event, I have already  ordered a Malpassi Filter King…

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  • Unkel Kunkel changed the title to Excessive Fuel pump pressure? ….solved

Paddocks offered a full refund adding they had not had similar problems reported to them from a large batch of pumps.

Meanwhile, I read the manual* againAA3C18DA-057E-4C0E-BCA9-37FC6BAB308E.thumb.jpeg.5ef5eadaf6a768c90e42f87e339c8a6b.jpeg

I was a bit doubtful about this working  and it sounded a right faff ..

- would be worth a try.

2 Flexoid paper gaskets plus a 1.5 mm  spacer made from fibre gasket material off cut plus the pump gasket ..

I was surprised:

the pressure was  now down from 7 psi to less than 2 psi.

Just the fibre gasket and the usual pump gasket it now gave  

3 psi which is in the 2.5-3.5 psi range.

I will keep it - (and the old pump in case  I need the spring )

It seems we must do a little “tuning “ with  gasket / spacers  for these pumps to suit our cars needs.

and the regulator is now on its way..

* RTFM .. read the f manual 

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22 hours ago, Pete Lewis said:

looks like there will be a high demand for cornflake packets !!!!

pleased  a relatively simple idea has fixed the over fuelling 

whats next  ha !

Pete

I have a large amount of cardboard from cereal packets - it’s good quality card and has a thousand uses !

( I was into recycling in the days when it was just called being mean)
 

I used gasket paper off- cuts 

E75D3CAB-9308-4F6F-ACC4-65ADDFFBA002.jpeg

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I installed a new fuel pump earlier this year as one of the valves had failed in my old one, but I kept the lower part of the original (casting, spring and previously replaced diaphragm) and simply swapped the tops, which worked fine. A simple way to avoid the pressure issues some encounter.

Gully

 

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  • 2 weeks later...

There seems to be two problems with these Powertune pumps:

 

Problem (1) .Pressure too high iro 7 psi instead of 2.5 -3.

Problem ( 2).   Very rough -sharp even, shoddy finish to the operating arm  that runs on the camshaft.

(1). is caused by the spring which pushes the diaphragm upwards after it has been compressed on the cam.

Just looking at the “old” spring and one from a new pump they are obviously different.

The new spring is slightly longer and thicker gauge.

Even allowing some age related change, there is a very obvious difference  when you squeeze the springs  and a crude  test using the kitchen scales shows  3.1 Kg needed to compress the old v 5 Kg for the “new” one.

( 2).The operating  arm  is made from a stamping but has simply not been “finished” leaving a rough finish is so ragged that I would think it could damage the cam.

The rest of the pump seems to be OK.

I had lowered the pressure by increasing gasket thickness, but  have since removed the pump and swapped over the springs.

I worked on the rough operating arm to obtain a smooth finish.

 

Annoyance - These jobs were no big deal deal, but slightly  annoying to have to adapt parts which are supposed to be “straight replacements”

Safety - It could be argued that a component delivering a pressure  so well outside  of specification that fuel  leakage occurs is safety issue. 

 

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Poor mans fuel injection🙄
I was fiddling with a pair of recalcitrant Amals on a vintage car recently and the only way I could make it run without dying was to wind the fuel pressure up till it would idle. I had removed the original pump from the engine bay and fitted a modern one with an adjustable regulator under the floor behind the seats so I could lean back and adjust the pressure while it was running. Didnt need any throttle to idle at 2000rpm just lots of fuel.

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