Lotus Elan

40 DCOE Type 31

PostPost by: PeterNev » Mon May 06, 2013 8:09 am

Hi

I have just got an elan +2 and am having problems getting to run well. It has the original type 31 Webers fitted with 45F8 idle jets and 110 mains jets on a F11 tube.

It will tick ove OK but has no power when opened up.

I have changes the nedel valves but it is still running very rich on the main jets and is spilling fuel out of the air horns. The fule pump also appears to be running all the time.

Any ideas (should I be changing to new carbs?)

Regards

Peter
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PostPost by: gjz30075 » Mon May 06, 2013 10:51 am

Sounds like you have an electric fuel pump, which is non stock. It's pressure should be about 3 psi, maybe less, if I recall. Those with electric pumps will chime in.

Have you checked the balance of the carbs with something like a Unisyn?

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PostPost by: types26/36 » Mon May 06, 2013 11:51 am

I would not "assume" that the carbs are the problem, have you checked basic settings like ign timing and (point gap) if fitted, is the distributor advance working OK? is the valve timing correct? have you done a compression check? what is the history.....did the problems just start or has the engine being rebuilt?
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PostPost by: Esprit2 » Mon May 06, 2013 6:30 pm

I agree it's generally not good to assume it's the carbs without considering other systems; however, the fact that the fuel is running out of the inlets and the pump runs all the time does indicate there are issues higher in the pecking order than the ignition.

If fuel is running out of the inlets, then it's likely that either the float/ inlet valve is not operating properly, or the fuel pressure is too high and over-powering the inlet valve. In either case, the float bowl will over-flow, and the mixture (if the engine runs at all) will be excessively rich.

Check the inlet valve to see if it's shutting off cleanly. Clean or replace it as required.

Check the condition of the floats. Shake them and listen for any fuel sloshing around inside of them. If fuel has leaked in, then replace the float.

If the floats are good, then check the float height setting and adjust it as required. Weber's stock spec for the DCOE-31 (brass hockey puck floats) is 8.5mm height, and 15mm droop.

DCOEs don't like high fuel pressure, and run best at 1.5-2.5 psi. If the pressure is too high, it can over-power the inlet valve and over-fill the float bowl. Since the car is equipped with an electric fuel pump, there's some cause to question if the fuel pressure is correct. Check the pump for markings indicating the rated output pressure, and/or use a fuel pressure gauge to check the pressure at the inlet.

If the pressure is high, then the easy solution is to leave the pump in place as is, and add an inline adjustable fuel pressure regulator as close to the carb inlets as practical. Set it to 2 psi.

Fuel can also leak out the inlets if the chokes are not properly secured in the throats. Check that the assembly is correct.

Those items should address the typical fuel leak sources.

*~*~*

Is the fuel old? If it's gotten old sitting in the car, then it's very likely the carbs need to be cleaned. At a minimum, remove the main and idle jet assemblies, along with the pump jets. Hold them up to a light and look through them. If they're plugged to any degree, clean them so the orifice is unobstructed.

*~*~*
The engine will run like crap if the carbs are not accurately balanced. That's a subject in itself, so I won't go there now other than to say check the balance. If you don't know how, I can forward a Word.doc with instructions.

*~*~*
When the engine is running and at least idles well, set the Idle Mixture Screws. If you need help with that, details would also be in the Word.doc.

Pick up a copy of Des Hammill's book, "How to Build & Power Tune Weber & Dellorto DCOE & DHLA Carburetors". An ackward title, but a very helpful book.

Regards,
Tim Engel
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PostPost by: Esprit2 » Mon May 06, 2013 7:25 pm

PeterNev wrote:I have just got an elan +2 and am having problems getting to run well. It has the original type 31 Webers fitted with 45F8 idle jets and 110 mains jets on a F11 tube.
(Snip)...
Any ideas (should I be changing to new carbs?)
Do you have the Workshop Manual? If so, the jetting set-up is listed in the carburetor portion of the Technical Data section. I don't have access to the manual now, but from memory, I would have expected something larger for the Main Jet... 110 just strikes me as a bit small. Can anyone check that?

The F11 Emulsion Tube sounds right, but I think the idle jet is also a bit small.

None of the above accounts for fuel running out of the inlets. Resolve the main problem first, then play around with jetting.

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PostPost by: denicholls2 » Tue May 07, 2013 3:53 pm

Sorry to say, I think that well-meaning but not very clear thinking contributors are encouraging you to mess with things that are clearly not problematic.

Your car runs like it is way too rich.

When you look into the carbs, fuel is flowing out of the needles at a rate that suggests an over-rich condition.

I strongly suggest you pay attention to these clear and irrefutable signs of a serious problem and ignore all else until that problem is corrected. If you don't, you will likely make the car stop running at all and make it much more difficult to get it back the way it was. While your jetting may not be ideal, and your ignition may be sub-optimal, these clearly aren't your immediate problem. Stay focused on your immediate problem and you will likely find when you fix it all else is fine (unless you messed with it in the meantime!)

Other posters have suggested that an electric fuel pump without proper regulation is the most likely suspect. I agree. So make that not a problem. Physically, the float bowls will fill quickly with an electric pump, after which you will have enough fuel available to diagnose further. So,

- Disconnect the pump power.
- Start the car.
- Note whether it smooths out. You have to let it burn that excess fuel away from the combustion chambers.
- If it stops running, reconnect the pump just for a few seconds to fill the bowls again.
- Repeat.

If the car runs smoothly with the pump off until it uses up the fuel in the bowls, your problem is in fact isolated to either the pump pressure or the inlet valve. My bet is on pump pressure.

My Europa is lucky enough to have an electric pump that self-regulates within the happy zone of the DCOE. but don't count on this. Regulators are inexpensive and will, if your pump is on the high end of acceptable, result in a more consistent mixture and probably lower fuel consumption.
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PostPost by: EPA » Tue May 07, 2013 5:53 pm

I would also check the cold start devices as they sometimes don't return properly and can cause problems.I don't think most owners actually use the so called choke very often and on the occasions it is used it can stick in a slightly on position.


Good luck
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PostPost by: PeterNev » Mon May 20, 2013 4:00 pm

Thanks for all of the advice. I have foun a problem with the cold start circuit and have disabled, this has stoped the fuel driping out of the intake. The car will still tick over well and will rev when standing still but when trying to drive it has no power and misfires. I have checked the timing and it is looking ok.

Any more advice ?
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PostPost by: Quart Meg Miles » Tue May 21, 2013 10:23 am

Fifty years ago a friend's Norton 500 had your problem, it would run but had no power, and it was the condenser in the distributor (the can with a wire on it). Replacing that was the cure, a long shot perhaps.

Was your ignition timing check just a static position one or a strobe light with a running engine? I'm wondering if your advance/retard is working properly which might give your symptoms.

My second hand 31s eventually ran rich causing misfiring at moderate speeds and, for a few years, I modified my slow-running jets to fix it but I don't think you're in that arena. (New 151s also ran rich, including after a full engine overhaul, so I still have to run modified jets).
Meg

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PostPost by: EPA » Thu May 30, 2013 7:57 pm

The rich running may have fouled the plugs which causes misfires etc and takes a while to clear ,that's assuming it ever does. I would try a new set of plugs now that the cold start device has been resolved. You could try cleaning the existing plugs but a new set would eliminate the possibility.
I find BP6ES work better than the BP7 for normal road use.
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PostPost by: AHM » Thu May 30, 2013 8:04 pm

Have you set the float levels?
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