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fuel pump problems

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pvergon

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hi there, again i´m in deep trouble. i´ve changed three fuel pumps already and the car is not working properly.

i have a TR4A with 87mm diameter cyl, which makes it a 2.2 lt (right?), with a mild street camshaft, oversize valves and ported cyl head.

to compensate all of this i decided to install two DHLA dellorto carbs.

i tried using the original fuel pump but apparently the fuel amount that got to the carbs was to poor.

i have already installed an electric fuel pump 5 to 7 pound of pressure on the back part of the car, right next to the gas tank, but it didn´t last more then 15 kms or 10 miles.

apparently the quality of this pump was too poor, cause i think it overheated.

i now installed a 15 pound and no luck cause it overfloded the carbs.

does anyone have an idea of the ideal fuel pressure for these carbs? do you think the mechanical fuel pump, the original should work? mine was new, but it did not work

by the way, every attempt i´ve overrun the mechanical fuel pump so pressures do not add.

i do need help and if you can think of any specific brand please let me know, i can always but anything through the internet.

thank you ... paul.
 
Well 15 pounds sounds like a lot of fuel pressure for a carb. The original AC mechanical pump spec was 1.25 to 2.5 pounds and that is adequate for the little 'sips' the SU takes from the bowl.

I know nothing about the carbs you have but would think an adjustable pressure regulator might be useful. Then you could dial in the pressure that is adequate but not too much.
 
Hi Paul,
I agree with George. Anything over 3 psi is too much pressure for your carbs. The float valves just can't hold any higher pressure & the carbs will flood. Use a pressure regulator or a different pump. The standard SU pumps are specifically designed to have low pressure.
D
 
Hi,
From the engine work you describe the stock fuel pump should be more than ample. 1.5-3 psi would be the working range you need, mechanical or electric. A fuel pressure regulator is a plus but isn't critical under 3 psi.
What are the symtoms ?
Check you filter. If you use a glass reusable filter they are prone to clogging. Do the basics first. Make sure you are getting an even supply of fuel to the carb, if you can measure the pressure that would be good. Check the lines for air leaks, colapsed or restricted lines. Once you have gone over the supply end for fuel move to the business end. Find out the float setting, if the venturi & jet size is proper. Chances are you will have to de-tune the carbs for street use.
I'm using a 2.5 psi mechanical fuel pump on a much more developed motor & a single SU HD8 with no problem.
Get back with more details.
 
I run twin Weber DCOE sidedrafts on my TR3A. I know the Dellorto sidedrafts are nearly identical. The stock mechanical fuel pump will furnish the correct fuel pressure. I do not run a mechanical pump because I had one fall apart (it was a reproduction with its rocker arm made from 3 layers of pressed steel riveted together). I had an expensive low pressure electrical points type that that worked well but lasted only a few years. I finally replaced it with a solid state Facet 2.5 - 4.5 psi (Pegasus Racing Supplies #1102 $44.79) and a pressure regulator set at 3.5 psi. The pressure reg is an inexpensive Purolator, I think (My son runs triple Webers on his TR6 and used an expensive regulator that went out quickly and he, too, now uses the Purolator). This system has been working well for about 5 years now.
 
Heres my experience with fuel pumps in my car. I had my mechanical pump in my TR6 fail twice on me, once before a rebuild and once after, so I went with an electrical. First I was using an electric pump out of a late 70's Mazda RX7, which operates on the same principle as the more expensive facet pumps. I accidentaly shorted that pump a few months later and killed it and decided to go with the facet as it is more flexible in mounting options (the Mazda pump has the nipples welded right to the pump body and one side has a right angle to it). Moss wants an insane amount of money for the facet pump, so I eventually found the best price online at a VW dunebuggy supplier in Texas, less than half what Moss wanted. Made up a nice block off plate from a piece of stainless for the mechanical pumps hole in the block, bent up some custom hard lines to make everything look nice, and wired a cutoff switch up under the dash. I also mounted the pump on rubber bushes to cut down on vibration, as these pumps do tend to chatter quite a bit. I can look up the suppliers name if you're interested. I've had that pump on the car for two years now and no problems, no flooding the carbs or anything, it's run flawlessly.
 
I've used the Facet pump for years with both the current SU's and the previous Webers. I have a filter between the tank and the pump. I also use a pressure regulator. Remember to use a T in the fuel line when using a pressure guage to set the pressure regulator.
 
Correction: Set the pressure regulator 2.5 - 3 psi instead of 3.5. I just checked with my son and also looked at the setting on my car.
 
hola a todos!!! i wanted to let you know that i followed your advice, i did check the fuel presure with a special gauge and you were all correct. the fuel presure was too low because of a bent fuel pipe line caused by a recently installed stainless steel fuel tank.

i appreciate all your help.


muchas gracias,

paul.
 
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