Lotus Elan

Weber float heights

PostPost by: daverubberduck » Sun Apr 02, 2017 1:04 pm

Hi All
I have been setting the float heights on my 40DCOE31 webers using the 8.5mm and 15mm spec. Car is early +2. Reading through all the threads on this subject, I see that the better method is to measure the fuel height in the main jet chamber. Method I used was as follows: removed one main jet from each carb and ran the engine for a short time, then stopped it. Then I used one of those thin tubes you get with cans of spray such as WD40. I taped a piece of card to it and dropped it down into the chamber up to the piece of card, put my finger over the end, pulled it out and measured from the card to the fuel level.

My problem is that I always get about 20mm. I tried increasing the height of the float a bit, thinking that this would close off the needle valve sooner (correct?). This didn't seem to make a difference. I recently replaced the fuel pump with new glass top one and I also replaced the needle valves. Prior to doing these things the carbs were flooding. The carbs no longer flood but why do I get 20mm fuel level? Is my method at fault? Should I be using an optical gauge with acrylic rod?
Dave
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PostPost by: ericbushby » Sun Apr 02, 2017 1:49 pm

Hi Dave,
You should be aiming for 25 mm from the top of the float chamber according to Keith `Watsit` at Sidedraft central,
The dipstick method works fine for me. I use a Vernier depth gauge and a torch. You can see the fuel shiver when the probe touches it. With the gauge it is easier for me to use the measurement of 41mm from the rim of the jet cover. A marked dip stick would be just as good. Even Keith, who invented the acrylic rod set up, now recommends a paper dipstick.
Surely lowering the float, not raising it, would cause it to shut the valve at a lower level.
Hope this makes sense,
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PostPost by: prezoom » Sun Apr 02, 2017 2:47 pm

Another thing to do is, make sure the floats do not wobble on the pivot pin. It takes a bit of time to adjust the clearance on the metal tabs of the floats so they can pivot and not stick but not wobble sideways. I went through this drill last night on a set of new to me carbs.
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PostPost by: daverubberduck » Sun Apr 02, 2017 5:36 pm

Hi Eric
I meant increase the gap above 8.5mm, which is in effect lowering it.

Well I think my method does not work, though I'm not sure why. Possibly fuel climbs up the narrow tube by capillary action. Anyway, I used your method of the vernier gauge and a torch, and like you I used 41mm from the top because my vernier was too wide to fit inside. Sorted it now.

Many thanks for your help.
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PostPost by: ericbushby » Sun Apr 02, 2017 6:13 pm

Dave, good!, I am glad it worked. It makes me want to try that thin tube in some petrol on the bench to see why that didn`t work.
Cheers
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PostPost by: daverubberduck » Mon Apr 03, 2017 9:11 am

Ah, a true scientist. Let me know what you find.
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PostPost by: ericbushby » Mon Apr 03, 2017 11:43 am

Oy , that's not fair, dumping it back on me!
The idea was to inspire you to try it. It was your problem in the first place and your theory of why it didn`t work.
OK, so be it.
I have found that if you immerse a transparent WD40 tube in petrol then the fuel runs up the inside of the tube 10mm above the outside fuel level, regardless of the depth of immersion. ( provided the tube has been in petrol earlier).
There, you were right about the capillary action.
Can I go back to weeding now in the sunshine.
Cheers
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PostPost by: daverubberduck » Mon Apr 03, 2017 6:00 pm

That's very interesting, you should write a paper on it now :)

Thanks Eric
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PostPost by: Grizzly » Fri Jun 22, 2018 7:35 pm

.......
Last edited by Grizzly on Tue Jul 03, 2018 7:45 am, edited 1 time in total.
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PostPost by: Terry Posma » Mon Jun 25, 2018 6:13 am

This may appear a dumb question!

There is much discussion about the fuel level being 25mm from the top of the chamber where the emulsion tube sits in but if you take out the ET surely the fuel level drops?

I am just looking at this again as I am trying to tune in an easier cold start without resorting to a choke mechanism.

A bit of reading in Sidedraft Central leads me think that a fuel level at the bottom of the of idle fuel passage is the optimum position and this is 25mm from the top of the float chamber, but when you measure the 25mm after you have extracted a ET, then the reading must be incorrect???

Can anyone set me straight?
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PostPost by: nmauduit » Mon Jun 25, 2018 9:16 am

it would drop a bit but the whole chamber would compensate most of it... and if one considers it a reference, as long as it's always measured consistently this would produce consistent results (different ET would have very similar volumes in their lower area)
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PostPost by: john.p.clegg » Mon Jun 25, 2018 11:02 am

I think you can take the measurement with the engine idling , or , while the engine is idling take out the tube and turn off the engine if the vibrations are too much....

Unless you have an electric fuel pump ....

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PostPost by: oldchieft » Mon Jun 25, 2018 10:04 pm

I have had several shots at setting the level on the car and found it next to impossible.

The man who seems to be the go to guy on this subject is Keith D. Franck.

In his white paper he says "Ideally, this should be done while the engine is idling and level."

My guess is this would be to have the float operating under "live conditions" of flow in and out via the idle system.

To get to a situations where I was not pressured while doing this job I have made a rig to do this job with the carb removed from the car and with the desired flow conditions.

First I made a bottom cover with a drain valve to give a simulation of a running engine.

img_1341.jpg and


Then a rig to give the same angle as the mounting on engine. (in my case 2 degrees back slope)

img_1339.jpg and


This is then fitted with a feed from a SU pump from a can and a drain back to the can.

After that I was able to mess with the top cover at my leisure and at last got the acrylic rod to work, but found that a screwdriver with a o ring on it worked better.

It still took a while to get it spot on but it was a fairly stress free job this way. Not many would be inclined to mess about like this but if others are finding this a difficulty they might like to try this way.

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PostPost by: Chancer » Tue Jun 26, 2018 9:58 am

Jon.

Did you also try it with the float chamber full valve closed and not under fuel flow conditions to see if it was any different?

If there was and the setting does indeed need to be done with the engine running then I really like your set up as there is no vibration or shaking of the fuel level.
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PostPost by: oldchieft » Tue Jun 26, 2018 9:25 pm

Chancer wrote:Did you also try it with the float chamber full valve closed and not under fuel flow conditions to see if it was any different?


No, I was long past the point of experimenting and research I just wanted to get it done and move on and I had spent too long messing around and getting annoyed.

Old age is not fun when the daffiest little job is a major work up.

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