john_p_b
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| posted on 17/3/06 at 06:42 PM |
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fitting twin 40's
well i think i finally have everything sitting here in a box that i need to fit the 40's to my pinto. i just have one thing that i can't
figure out.......should there be a return for the fuel?
i've got obviously line out the tank to the pump, pump to the pressure regulator, pressure regulator to the carbs but there's no way back
for unused fuel?
is this just how it is with twin carbs or am i missing something?
also as the mechanical lift pump won't be in use anymore am i ok to simply leave it there for the time being until i make or source a blanking
plate or will this cause other problems?
cheers
john
built a car, built a home, had a family. lost the family, lost the home, still got the car.
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britishtrident
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| posted on 17/3/06 at 06:47 PM |
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Just use the ordinary carb pinto mechanical lift pump connected directly to the carbs nothing else is required. ie no regulator no return line
required.
[Edited on 17/3/06 by britishtrident]
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JoelP
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| posted on 17/3/06 at 06:49 PM |
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if your pressure regulator works well, you dont need a return. If its not working, you'll have fuel leakig from your carbs, which should be
noticable and easy to fix. If you have no joy with the pressure regulator, just use a bike pump. Some people find they cant turn the presure down
enough, others manage just fine. 
As for your old pump, i have no idea. Sounds like a good idea to move it though, it gonna cost you a bhp or 2 turning it for no reason!
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john_p_b
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| posted on 17/3/06 at 06:58 PM |
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quote:
Originally posted by britishtrident
Just use the ordinary carb pinto mechanical lift pump connected directly to the carbs nothing else is required. ie no regulator no return line
required.
[Edited on 17/3/06 by britishtrident]
i didn't think the standard lift pump would pull enough fuel through to make the 40's effective? if it does then great as i then
wouldn't have to start wiring in a pump at the back etc etc but i've already bought a bloody pump now!!!!
built a car, built a home, had a family. lost the family, lost the home, still got the car.
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john_p_b
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| posted on 17/3/06 at 07:01 PM |
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quote:
Originally posted by JoelP
if your pressure regulator works well, you dont need a return. If its not working, you'll have fuel leakig from your carbs, which should be
noticable and easy to fix. If you have no joy with the pressure regulator, just use a bike pump. Some people find they cant turn the presure down
enough, others manage just fine.
As for your old pump, i have no idea. Sounds like a good idea to move it though, it gonna cost you a bhp or 2 turning it for no reason!
the regulator is a brand new filter king item coplete with a little gauge and everything!
my only concern was when i first started running with my standard carb i was getting flooding leading to a nasty puddle on the garage floor and the
threat of the whole thing going up in flames! fitted the standard sierra swirl pot with return (think i actually got that of you joel?) and it sorted
it no probs!
built a car, built a home, had a family. lost the family, lost the home, still got the car.
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keith2lp
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| posted on 17/3/06 at 08:19 PM |
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Hi John
I run twin 40s and use the standard fuel pump with out a regulator and every thing is fine. I dont get any overflowing problems and it supplys enough
fuel for every thing I have thrown at it.
Keith
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britishtrident
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| posted on 17/3/06 at 08:20 PM |
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quote:
Originally posted by john_p_b
quote:
Originally posted by britishtrident
Just use the ordinary carb pinto mechanical lift pump connected directly to the carbs nothing else is required. ie no regulator no return line
required.
[Edited on 17/3/06 by britishtrident]
i didn't think the standard lift pump would pull enough fuel through to make the 40's effective? if it does then great as i then
wouldn't have to start wiring in a pump at the back etc etc but i've already bought a bloody pump now!!!!
Lotus used a standard Ford AC mechanical pump on the twincam engine, the BDA also had the same pump, Rootes used a standard mechanical AC pump feeding
twin on the Holbay Hunter engine.
The pinto is a slow revving engine if the pump is in decent shape it souldn't be a problem -- different matter if you have an engine spinning
it at 10,000 rpm.
[Edited on 17/3/06 by britishtrident]
[Edited on 17/3/06 by britishtrident]
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john_p_b
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| posted on 17/3/06 at 09:06 PM |
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looks like a regulator and pump may soon be seeing there way on to ebay then if i can pipe it in simply via the lift pump!
thanks folks
built a car, built a home, had a family. lost the family, lost the home, still got the car.
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DIY Si
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| posted on 17/3/06 at 09:18 PM |
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You'd be suprised how much a standard pump an deal with. They tend to be capable of more than the engine requires in case it's needed on a
uprated version of the engine, or in ford's case for use on several engine types. My standard 20 year old mini pump handles my 145/150bhp engine
just fine. It'll put up with a very spirited drive of 40 mns without a problem. The other thing is, although your engine may have more power
than standard, you aren't using it all the time, so when you back off the power a bit, the pump has time to catch up and refill the float
cambers if they are getting empty.
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britishtrident
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| posted on 18/3/06 at 07:44 AM |
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quote:
Originally posted by Dave Ashurst
John
Electric pump and regulator is the safe way to go in my experience (on a crossflow but the principle's the same).
I've had a fuel fire in the engine bay due to overpressure caused by using an unregulated mechanical pump with twin dcoe 40s and no return pipe.
Note that an unregulated mechanical pump simply delivers fuel to the carbs in proportion to the speed of the engine. It takes no notice of how much
fuel the engine needs.
On overrun (throttle closed) at high rpm it supplies too much. If you drive enthusiastically you will get overpressure in twin 40 dcoes resulting in
fuel leakage from the intake trumpets into the air filter(s).
My fire started when fuel leaked into the air filter was ignited by a pop from the carbs. It was a very hot day, been driving hard, I'd been
decelerating to a sharp bend, and I'd changed down a gear.
There's a real risk of running lean too. Sustained full throttle driving with a mechanical pump on 2x40s CAN cause fuel starvation.
I wouldn't risk it.
regards
Dave
This is just plain wrong
A mechanical fuel works exactly the same way as an SU electric diaphram pump --- a spring does the pumping and controls the pressure and the
mechanical or electrical bit does is drives the pump on the suction stroke compressing the spring - hence you get the same pressure at idle as at
6,000 rpm.
If a mechanical pump is supplying too much pressure it can only be because the the pump has been incorrectly fitted (ie the spacers has been ommitted
between the pump the cylinder block) or (much less likely) the diaphram has went hard with age.
[Edited on 18/3/06 by britishtrident]
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Dave Ashurst
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| posted on 18/3/06 at 04:05 PM |
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Thanks for the correcting me Trident.
I was wrong. I just tested an old one and yes the mechanical pump does have a delivery pressure limit. How interesting.
However, it is true that for whatever reason my mechanical pump and carbs were incompatible and the carbs leaked fuel at high rpm overrun as
described. It was observable on the rolling road too.
Since the carbs were well serviced and adjusted I'd always blamed the mechanical pump! I live and learn.
regards
Dave
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