Lotus Elan

Strombergs flooding

PostPost by: deep_socket » Fri Jun 10, 2005 2:49 pm

This is my first post, having (after 30+ years) finally succumbed to Lotus disease. Like Stuart, I just acquired a 72 Elan Sprint dhc. A blast!

I've been following this forum with great interest, and hope someone may have a suggestion regarding the following.

Car had been running a bit rich, but basically fine. Then, abruptly, it wouldn't start. Flooded. At first, only when hot, now all the time.

Will not start at all. Raw fuel drips from airbox. Pull off airbox, both carbs wet. Crank over and fuel spurts from the hole above and to the left of the throat of both carburetors. Not good.

Seems like needle/float problem, so...take apart both carbs. Clean, no gunk, corrosion or grit. Floats look fine. Loose rivet on one, where the metal arm attaches to the plastic--no leak, and seemingly not a big deal, but fixed that. Replace both needle valves, reset float height at 17mm, replace both diaphragms (why not...?), put all back together, and...

...same problem. And it affects both carbs.

I'm not finding anything in Haynes, and now that I've had the carbs apart I really can't see what (besides needle/float) could be at fault.

Any words of wisdom for a newbie?

Bob
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PostPost by: steveww » Fri Jun 10, 2005 3:42 pm

Has the car got an electric fuel pump? These supply too much pressure and can override the needle valves in the float chamber.

Check the needles and jets for wear groves.

You really need to set the mixture with a CO meter, aim for 5%.

The hole where the fuel is coming from is the float chamber vent IIRC.
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PostPost by: deep_socket » Fri Jun 10, 2005 5:22 pm

Steve:

Thanks for your reply.

If fuel pump overpressure was overwhelming the needle valves, that would explain why both carbs are affected....but the fuel pump is mechanical. Can a mechanical fuel pump suddenly start putting out too much pressure?

I checked the old needle valves and they looked OK, but I replaced them with new ones anyway. That didn't help.

I'll check the fuel pressure (which I'm guessing should be something like 2 or 3 psi?).

Bob
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PostPost by: DrEntropy » Sat Jun 11, 2005 10:21 am

Seems unlikely a mechanical pump would suddenly develop higher output pressures, but that sounds like the problem. Odd, that.

IMHO, 2~3 lb/sq' would be fine, nothing over five(!), whether Strombergs, S.U.'s or Webers. I have run electric pumps on my Weber'd Elans for years, with pressure regulators in line to guarantee proper (low) pressures. Went so far as to mount an S.U. electric pump from an MGB in the baby Elan. I've also done this to many, many clients' English Ford cars over the years.
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PostPost by: deep_socket » Mon Jun 13, 2005 12:51 pm

Gentlemen:

Looks like you were right: the pump is delivering a steady 6 psi, which is obviously too high. The manual calls for 1.25 to 2.5 psi.

Hard to see how a diaphragm pump could suddenly start doing that--one would think that in most failure modes, such as if the diaphragm return spring broke, the result would be the opposite.

I guess I had better replace the pump, since something is obviously amiss. Any votes for just installing a pressure regulator?

Dr. E: If I go the electric fuel pump route, what is the best site--in the boot? I assume it would be wired to the ignition hot lead. And what is the best place for the pressure regulator? And what do you do about the old mechanical pump--just blank off the inlet and outlet and leave it in place?

Thanks for your help.

Bob
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PostPost by: type26owner » Mon Jun 13, 2005 1:20 pm

6psi is the normal output pressure of the mechanical pumps. A pressure regulator is required to reduce the pressure. I use a Filter King brand which is made in Italy.
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PostPost by: steveww » Tue Jun 14, 2005 4:38 pm

On my S4 I have an electric fuel pump in the boot (trunk) under the boards next to the tank. I have a Filter King in the engine bay as cloase to the carbs as possible. I can send some pictures if you want.
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PostPost by: deep_socket » Wed Jun 15, 2005 2:18 pm

Fuel pressure it is!

A Pro Fuel regulator from Dave Bean set to 2 psi does the trick.

Thanks for your input.

Bob
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