Lotus Elan

weber carb tuning

PostPost by: robb4100 » Tue Jun 10, 2008 11:14 am

Hi Guys,

The car is running much more rich right now than it was before I pulled hte engine for clutch work and changed to negative earth.

I just pulled the main juts. F11; 190 and 110.

THe bottom half of the Jet is also wet with fuel when I pull it out. I do not remember this being the case 2 years ago the last time I looked at the jets. Is this normal? The floats seem fine and the fuel level seems fine in the carbs.


If you were starting to make adjustments would you go to 200 on the air or drop the fuel to 105?
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PostPost by: rgh0 » Tue Jun 10, 2008 12:10 pm

Rob

You are delving into an area of incredible complexity - go to the Yahoo group "Sidedraft central' and read the posts and related files data to start to see what you may need to do.

And yes the bottom half of the jet should be wet with fuel - what the precise correct fuel level is - that another matter - see Sidedraft central

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Rohan
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PostPost by: ppnelan » Tue Jun 10, 2008 4:38 pm

Changing the clutch & converting to negative earth should not affect the carburettors :!: :shock:

Unless you are ABSOLUTELY SURE everything else is working as it should and the engine is unmodified, I would not start changing jets from the original specification. Lotus were pretty good at their job... :wink:

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PostPost by: twincamman » Tue Jun 10, 2008 5:09 pm

carburettor is french for leave it alone -----balance them ---set the idle jets after a run and change the points ---ed
dont close your eyes --you will miss the crash
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PostPost by: robb4100 » Tue Jun 10, 2008 8:01 pm

I am getting about 10 miles to the gallon and the plugs are a uniform black mess! I'll replace the plugs and see if I get the same result before ignoring the leave it alone advice.

With the negative earth conversion I also needed to swap the electronic ignition although it is the same brand.

Could this be the "sloshing"of fuel that I have heard can happen if the carb mounts are too tight?

The car has always been a little rich but this it the worst it has been.

robb
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PostPost by: Chrisrich » Tue Jun 10, 2008 8:32 pm

One could think it more than a coincidence that you're swapped out your ignition system and are now having this problem. Some really smart guy once told me that 95% of all carb problems are really timing/ignition problems in disguise. Perhaps head off in that direction????
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PostPost by: elj221c » Wed Jun 11, 2008 9:55 am

Rob,

If you changed the polarity did you change it on the coil?
Did you take the carbs off when you pulled the engine. Did they get turned up-side-down? Check that floats are free and right height and that the needle valves are working correctly.
If it was running OK before why would you need to change jets? Webbers should only need periodic balance checks and maybe idle adjustment.

Roy
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PostPost by: ill_will » Wed Jun 11, 2008 1:02 pm

the idle enrichment circuits aren't jammed open or incorrectly set up are they? 10 miles to the gallon is unlikely to be a 'wrong needle size' type of problem i reckon. Could be the choke cable's incorrectly set up.

if you took the carbs off/engine out etc this could be a possibility. is there any evidence of excess petrol (i.e. dripping from the ends of the trumpets, or on the underside of the carbs?)

and are the blackened plugs on all cylinders, or just a few?

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PostPost by: ill_will » Wed Jun 11, 2008 1:02 pm

the idle enrichment circuits aren't jammed open or incorrectly set up are they? 10 miles to the gallon is unlikely to be a 'wrong needle size' type of problem i reckon. Could be the choke cable's incorrectly set up.

if you took the carbs off/engine out etc this could be a possibility. is there any evidence of excess petrol (i.e. dripping from the ends of the trumpets, or on the underside of the carbs?)

and are the blackened plugs on all cylinders, or a pair, or just one?

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PostPost by: trw99 » Wed Jun 11, 2008 2:55 pm

If you want to get really technical, look up some of the long and detailed posts by 'type26owner' on this forum. Keith was an alchemist with Weber tuning and we miss his input on here.

I believe he still posts regularly on the subject on this forum: http://www.innovatemotorsports.com/forums/index.php

Tim
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PostPost by: rgh0 » Thu Jun 12, 2008 11:35 am

trw99 wrote:If you want to get really technical, look up some of the long and detailed posts by 'type26owner' on this forum. Keith was an alchemist with Weber tuning and we miss his input on here.

I believe he still posts regularly on the subject on this forum: http://www.innovatemotorsports.com/forums/index.php

Tim


Keith moderates the sidedraft central yahoo group and is the best place to work on carb problems.

cheers
Rohan
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