Lotus Elan

Poor / no running - Weber Carbs

PostPost by: mbell » Mon Jun 06, 2016 6:40 pm

Gizze wrote:- There is still evidence of petrol in the air box, and I've noticed the large open hole near the air inlets (about 3/8" dia) on each carb has a small pool of petrol in them


Are you talking about the holes between the carbs and airbox above the left trumpet?

These holes should allow filtered air from the airbox to enter the carb bodies but you shouldn't be see any fuel escaping from them to the airbox. The only thing I can think of that would cause this would the fuel level being way to high. Either caused by incorrect adjustment or by a too high pressure fuel pump.

Have you checked the fuel level in the carbs? It should be ~25mm down from the top of the jet holder. Which is just below the outlet holes the main jet "tube". If it's above this hole fuel will just run through the carbs and into the engine and you'll have no mixture control at all.

You should be able to do a basic check by running the car with main jets removed and shine a light down the hole to make sure the fuel level is below the hole.
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: Gizze » Mon Jun 06, 2016 9:17 pm

Yes that's the holes.
I have set the floats in accordance to the manual but thought maybe the engine rocking about so much was part of the problem. Anyhow I'll try checking / lowering the fuel level again. Many thanks for the post.
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PostPost by: mbell » Mon Jun 06, 2016 9:36 pm

What fuel pump are you running?

If you running an after market one you need to make sure is is a low pressure (<3 PSI) or it can overcome the inlet valve in the webers and flood the carbs.
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: rgh0 » Tue Jun 07, 2016 11:10 am

The hole in the carb body is the vent from the float chamber. Fuel in there suggests that the fuel level is to high, fuel in the airbox also suggests the same though it can also be due to the chokes not being sealed well and fuel going through the main jet to the auxiliary venturi is leaking as the spring clip is not keeping the choke body firmly in place.

cheers
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PostPost by: davidc » Tue Jun 07, 2016 2:28 pm

apologies if this may come across as a stupid question but without researching you on the forum i'm don't know how mechanically minded you are! :oops:

your first post where you mention timing, you have got it right at 10 BTDC? what marks have you gone off, are they reliable.

again sorry if this seems stupid but reading through it looks like you gone through fuel and spark issues!
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PostPost by: Gizze » Wed Jun 08, 2016 6:01 pm

Hi All,
The pump is a mechanical one, and when the carbs were off I tried blowing through the fuel inlet with the float raised and there seemed to be a good seal - I know not very accurate but an indication...
I've tried removing the chokes but they wouldn't readily come out, that's not to say they are sealed but will need to persevere to get them out. The venturis came out readily though. How would I seal the chokes if they are leaking, have they got O rings or similar?
David C - Timing - no problem in questioning my ability on cars - I'm an enthusiastic amateur at best and often question my own ability! I've determined TDC by checking timing marks / valves /rotor arm position on distributor cap and then checked with a bulb on the 10 Deg mark on the crank, so I think this is ok for now but would like to dynamically time once the basics look ok.
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PostPost by: mbell » Wed Jun 08, 2016 9:39 pm

Have you checked the fuel level in the carbs yet?

It only needs to be a few mm too high and the fuel will be able to run in to the throats, which would cause significant mixture issues (very rich) and could run back into the airbox. It a very quick/easy test.....
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: Gizze » Fri Jun 10, 2016 8:06 pm

Yes will re-check the float levels again this weekend. As the shut off valve appears to work hopefully this is the problem
Many thanks
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