Lotus Elan

Weber idle too high??

PostPost by: Grizzly » Mon Jan 12, 2015 7:36 pm

Hi all.

I know this is going to sound dumb but i'm struggling to get my idle below 1300-1500rpm with the idle screw right out.

Thing is i automatically thought i had an air leak so i've removed the carbs, fitted new O-Rings and re-tightened very evenly making sure no one nut is any tighter or looser then the others. I then made sure the Servo/Headlight vacuum's where well blanked off and started it again (still won't idle) i sprayed some carb cleaner around the Inlet seals with no drop in rpm and the Carb balancer is saying there both more or less even.

The Carb's them self have been professionally rebuilt and the engine runs very smoothly but it just won't drop to 900-1000 rpm.

Have i missed some thing??
Chris
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PostPost by: mbell » Mon Jan 12, 2015 7:54 pm

My first check would be that the throttle plates are actually fully closing.

Remove the progression hole covers and shine a bright light down the carb barrel. You should be looking to see where the throttle plates are relative to the progression holes. Normally you should see light in all the holes especially with the idle adjustment at min. For a proper idle the throttle plate might need to obscure the first progression hole with the edge of the plate but normally the plate shouldn't be behind the first progression hole.

If your not seeing light from all the holes I'd take a look at your linkage to make sure it isn't holding the throttle slightly open. Are you testing with throttle cable disconnected?
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PostPost by: ricarbo » Mon Jan 12, 2015 7:57 pm

Something is wrong for sure. If the air supply can be adjusted to nil, then the engine will definitely stop. If you cover over the air intakes at the carbs, does it stop? Could need 4 hands, I suppose.
Have you checked the ignition timing?
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PostPost by: EPA » Mon Jan 12, 2015 8:16 pm

Have you checked that the accelerator cable isn't holding the throttle slightly open?
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PostPost by: bill308 » Mon Jan 12, 2015 8:56 pm

The normal relationship between the edge of the throttle plate and first (most down stream or most distant from the carb inlet) progression hole, at idle, is with the throttle plate just about to uncover the first hole. Further opening of the throttle valve progressively opens the second and third holes.This means at idle, all the air/fuel mixture is supplied by the needle valve adjusted hole, which is more down stream than the 3-progression holes.

I hope this helps.

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PostPost by: Grizzly » Mon Jan 12, 2015 10:02 pm

Thanks guys, i have a list of stuff to check so i'll let you know how i get on.

BTW, i have the Throttle cable off, it worries me slightly because my webers are original and the previous owner said he could never keep them in tune so i had a full rebuild done with new Shafts,roller bearings,Seals,Jets,Pump etc etc so they had allot of work and i suppose it only takes one thing a bit out of wack or the wrong part used?? but the place that did them came highly recommended so i'm sure it will end up being some thing simple.
Last edited by Grizzly on Tue Jan 13, 2015 2:06 am, edited 3 times in total.
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PostPost by: bill308 » Mon Jan 12, 2015 10:50 pm

In my post above, I wrote, "This means at idle, all the air/fuel mixture is supplied by the needle valve adjusted hole,.....". This is not quite correct.

In addition to the emulsified air/fuel mixture supplied by the needle valve adjusted hole, additional air is supplied by leakage past the throttle plate and by the air balance circuit if fitted (40DCOE151, 45DCOE152, and probably some models of Dellortos).

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PostPost by: oldchieft » Tue Jan 13, 2015 10:07 am

I would second the idea that the throttle plates are not centred

If you have the carbs off then slacken the screws on the throttle shaft and tap the discs.

When they are good the smallest feeler gauge you have should be trapped by the closed throttle.

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PostPost by: Grizzly » Tue Jan 13, 2015 3:46 pm

Bit of an update, I didn't have much time today to play with the car but i took the Carb's back off and in the process noticed one of the cold start levers was stuck. So took the lever mechanism off and one of the brass things the cold start lever fits into (excuse the technical term) was stuck so i put some wd40 in there and worked it a bit with the cold start mechanism and it has freed up.

Not tried them (there still off the car at the moment) but i'm tempted to strip them and check every thing properly. I know they where rebuilt but they have been sat on a shelf for almost a year.

btw, i checked the Butterflys and they all trap the smallest Feeler gauge i have, i also checked the flatness of the Head and Carb mating surfaces and also had a really good look at the o-rings for any nicks etc.
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PostPost by: Grizzly » Thu Jan 15, 2015 3:09 pm

Can any one tell me if there should be a seal on the Idling adjustment screw between the body and the spring on the Type 31 Weber Dcoe 40?

I ask because when the carbs went for rebuild there was no washer or seal, when they came back they had a washer/seal and they dont seem to bottom out when you tighten them?. Just had a quick look at my +2 and that doesn't have a seal??
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PostPost by: Lyn7 » Thu Jan 15, 2015 4:01 pm

Hi Chris, I presume you are talking about the idle mixture screws? :? If you are I don't believe there is a seal.
Good luck Lyn..
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PostPost by: Grizzly » Thu Jan 15, 2015 4:09 pm

Sorry yes, the four Idle Mixture screws.

I can only find Diagrams if the later Weber carb and they Do have them fitted?? so one one my cars is not right and i'm guessing its the rebuilt ones.
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PostPost by: mbell » Thu Jan 15, 2015 6:34 pm

My type 31's don't have a seal.
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PostPost by: Grizzly » Thu Jan 15, 2015 7:38 pm

Can anyone recommend a Book or source of Information i can do a bit of reading up on the DCOE?

I ran my +2 as an every day car for a few years and had a bit of a Ritual of adding Redex too every third tank of Fuel and cleaning the jets with every service (with a bit of an Idle balance and tweak) but never really got too involved so i'm finding out how little i actually know about them now :roll:
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PostPost by: richardcox_lotus » Thu Jan 15, 2015 9:00 pm

I got a copy of this & found it very useful - I'm not a mechanic & needed to read it a couple if times to make sure the chapter I was referring to was a weber and not a dellorto - but still very pleased.

http://www.amazon.co.uk/Build-Dellorto-Carburettors-Speedpro-Series/dp/1903706750
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