Lotus Elan

fuel leaking from Weber front and rear trumpets

PostPost by: NWElan » Fri Sep 25, 2020 11:01 pm

Hello all,

Upon start up and idling, fuel weeps out of the front and rear most trumpet horns. Increasing throttle increases the fuel leak.

I've checked the fuel bowl floats and needle valves and they move freely and no obstructions.

Any suggestions what else to check for the source of the leaking fuel?

Thanks
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PostPost by: rgh0 » Sat Sep 26, 2020 12:17 am

I assume you have Webers. The 40DCOE have a spring clip in the side of the auxiliary venturi body that sprays the fuel. If this clip does not hold the body firmly in place then fuel can leak out around it coming out at the base of the trumpets.

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PostPost by: mbell » Sat Sep 26, 2020 1:10 am

Also if there fuel level is set to high it can be high enough fuel just runs out of the carb via the main jets.

I'd suggest checking the fuel level to make sure it's lower than the outlet to start with. You should be able to see that by removing the main jet stack and looking down the hole with the light. (Can do it with car running if needed.)

You also want to check the fuel pressure isn't too high (<3 psi). As that can prevent the needle valve closing, causing the carbs to flood.
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PostPost by: NWElan » Sat Sep 26, 2020 3:31 am

Rohan,

Thank you for your suggestion.

Where is the auxiliary venturi body? I can't find it on the diagrams that I have.

John
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PostPost by: mbell » Sat Sep 26, 2020 3:34 am

'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: sprintsoft » Sat Sep 26, 2020 8:02 am

Hi John,

I'm going to paraphrase Keith Franck who has long experience with Webers:

"Buy some EZ Turn from an aircraft supplier.... ...Use the EZ Turn sealant around the outside of the airhorns to make a fuel tight seal to the carb body. Otherwise they dribble fuel out constantly.."

further as Rohan mentioned:

"Those P-shaped springs are junk and the AV can be too loose to work properly. If you can stick your finger down into the AV nacelle and jiggle it around then it is too loose..."

You can find Keith on here, with some really good discussions:
http://groups.yahoo.com/group/sidedraft_central

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PostPost by: NWElan » Sat Sep 26, 2020 5:37 pm

Hello again,

Checked float height by measuring float to lid distances and they are ok. Looked down main jet passage and fuel level is well below the hole to the venturi (the hole pointed to by letter A in the photo below). Tried to measure the distance from fuel level to the top of the well (the spot pointed to by letter B in the photo). The distance is about 30 mm instead of the 25 mm mentioned in other threads.

fuel level.jpg and

Is the auxiliary venturi nacelle the ring around the fuel nozzle in this photo? If yes, then mine are not loose at all though I don't understand where are the P-shaped springs.

auxiliary venturi.jpg and

The fact that fuel leaks from both carbs leads me to think perhaps excessive fuel pressure is the problem. However, no fuel leakage from the middle two airhorns (rear airhorn of the front carb and the front airhorn from the rear carb) is puzzling. I should have a fuel pressure gauge later today.
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PostPost by: mbell » Sat Sep 26, 2020 6:36 pm

The p clip are in the outside of the venturi so you can't see them unless you remove them.
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PostPost by: RichardHawkins » Sat Sep 26, 2020 6:44 pm

Spring soft,

Excuse me deviating from the subject. Where can you buy EZ Turn in the UK?

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PostPost by: sprintsoft » Sat Sep 26, 2020 6:54 pm

Hi Richard,

It's a US supplied product and you can probably order it from there, but I got mine shipped in 2 days from Germany:
https://www.aircraftspruce.eu/engine-parts/lubricants/ez-turn-lubricant.html

Regards
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PostPost by: sprintsoft » Sat Sep 26, 2020 7:00 pm

Hi John,

you asked:
"Is the auxiliary venturi nacelle the ring around the fuel nozzle in this photo? If yes, then mine are not loose at all though I don't understand where are the P-shaped springs..."

Yes, correct, and if they are not loose you don't have to worry about the P springs :)

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PostPost by: MarkDa » Sat Sep 26, 2020 9:55 pm

Don't think I'll be buying any EZ Turn - at €100 for 5oz tube to UK it's a bit steep!

On the other hand Morris Lubricsnts Red Rubber grease being vegetable based is resistant to petrol etc.
£16 for 500g

Now on track for veg grease - expect other brands as well?
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PostPost by: mbell » Sat Sep 26, 2020 11:10 pm

I think I just fitted orings on the air horns to seal them. Might have had to trim the air box to carb gasket to get them to fit.
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PostPost by: NWElan » Sun Sep 27, 2020 4:19 am

I added a fuel pressure regulator and tried pressure at 2 psi and 1.5 psi but doesn't solve the problem.

There is tremendous fuel blow back out of the carb throats when running. A film of fuel quickly coats the engine bay opposite the carburetors. More so at higher rpm.

I just finished re-installing the engine after replacing the water pump. The distributor advance is set to 10 deg BTC checked with a timing light. The engine starts up easily and idles but roughly.

What would be the symptoms if I re-installed the timing chain one tooth off?

John
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PostPost by: MarkDa » Sun Sep 27, 2020 6:10 am

I have a feeling that a degree of fuel mist coming out of the trumpets is 'standard'
It's why you should always use an air box to contain it - the fuel then gets picked up by the air flow into the carbs.
Without an air box as you say it ends up on the body waiting for spark to ignite it!
After my engine was rebuilt I observed it while it was being run in on a dyno.
Last edited by MarkDa on Mon Sep 28, 2020 4:49 pm, edited 2 times in total.
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