Weber float heights

[Chancer]

Tell me about it Jon!!!!!

[Grizzly]

I'm having a bit of a problem with my carb float set up.

The 40 dcoe 31 carbs in question where rebuilt by Webercon (full set of jets etc to Lotus specs) when i first got them back it ran very rich (plugs always black after a run). I rang and asked what float level they have been set to and was told 8.5mm....... When i dipped the carbs i was getting 16mm and 18mm which if the theory is correct means the fuel level is way too high (i used a cable tie to check the level, checked four or five times over a couple of days to make sure)

To get 25mm the tab on the brass floats is bent so far it's just touching the side of the needle ball (that can't be right surly?) when i run the car like that it pop's, bangs and is not happy.

Considering it still has the stock mechanical fuel pump fitted and the fuel pressure hasn't been played with it's odd..... i've reset it to 8mm using the old method and it run's again but quite rich again, it's starting to sound like they have used a wrong component some where along the line but i don't know much about these things (it's why i had them rebuilt by pro's)

Any idea?

[john.p.clegg]

Chris
I think you'll find the Lotus standard jetting is on the rich side,they prefer people to have power under their foot rather than pounds in their pocket....

You may get better jet sizes on here or from scouring the net..

John

[richardcox_lotus]

My fuel levels are 3-mm or so too low. I?m struggling to bend the tabs to get the right value. Is it really just so much hit and miss ??

For something that has to be so precise, it?s a very imprecise method !!!!

Regards
Richard

[Grizzly]

Chris
I think you'll find the Lotus standard jetting is on the rich side,they prefer people to have power under their foot rather than pounds in their pocket....

You may get better jet sizes on here or from scouring the net..

John

John, i agree i've never had a 'Lean' running Lotus but this is a bit extreme, on the other cars after a run i get a mid brown coloured spark plug, on this setup i've not seen anything other than black (well after a run it's more very dark grey but black for all Intents and Purposes).

I have been searching reasons why it is doing this and it keeps coming back to fuel level being too high, i even thought the needle valve may have been faulty/leaking but it holds 5psi of air fine so i can't see it being that.

I will have a search for better jet sizes but i think there is a fault. I spoke to Webcon who said to check there wasn't Plastic float covers with Brass floats fitted but i've checked the Floats for holes or damage and the covers (they are my original 31's)

So i'm stumped.......... i'm planning on taking a set of carbs off the +2 and seeing if it runs any better but it may be a waste of time as the fuel level appears to be correct on that (not sure it will tell me why the set is misbehaving)

[nmauduit]

To get 25mm the tab on the brass floats is bent so far it's just touching the side of the needle ball (that can't be right surly?) when i run the car like that it pop's, bangs and is not happy.

Considering it still has the stock mechanical fuel pump fitted and the fuel pressure hasn't been played with it's odd..... i've reset it to 8mm using the old method and it run's again but quite rich again, it's starting to sound like they have used a wrong component some where along the line but i don't know much about these things (it's why i had them rebuilt by pro's)

No idea but a side observation : if the valve is operating correctly, the fuel pressure should not play any role in fuel level (the valve shuts off the tap following a geometrical constraint, not a pressure constraint - the pressure is just a by product of flow, which is required to replenish the level at full throttle). Also theoretical float level depends on material (typical float clearance is around 8.5mm for brass floats, 12.5mm for plastic ones).

Could it be that the actual valve used are not of the geometry meant for the carb body (e.g. too short)? you may try to compensate for this with a setup of your own using a lower level, e.g. 22-23mm from the top and try it on the road... What I like with setting up the fuel level literally (and not by the float) is that it is exactly what the emulsion tube are seeing, so this method is impervious to all inaccuracies there may be along the line.

[Grizzly]

. What I like with setting up the fuel level literally (and not by the float) is that it is exactly what the emulsion tube are seeing, so this method is impervious to all inaccuracies there may be along the line.

I agree, it's why i'm thinking i have an issue with the carbs making it run way rich (not that TC's need to run any richer in the first place)

Do you know how tall the needle valve should be? or know anywhere i can find out?

I might pull one of the carb's to bits and check what exactly is in it.

[nmauduit]

Do you know how tall the needle valve should be? or know anywhere i can find out?

not off hand, but I would add I always try to use original Weber parts for rebuilds as I have had a tolerances issues with repros (esp. jets - may not apply to valves) ...

[Grizzly]

Not only was Weber parts used but it was rebuilt by a Weber main dealer which is why i'm confused. if the pair of carbs hadn't sat on a shelf for 2 and a bit years i'd be taking them back.

i must be missing some thing here........

[Donels]

Weber_DCOE_Tuning_White_Paper.pdf

(96.96 KiB) Downloaded 388 times

If you haven't already done so try reading the attached. It may help.

[Grizzly]

Thanks for that, i've not read Mr Franck's white paper but i will.

Just a bit of an update, i swapped the two float assembly's from my +2 and now the fuel level is bang on 25mm (using the Pipettes method to check), so at least it's not going to be a long list of stuff to have a good look at but it's strange.

[mbell]

Leaking floats?

Would cause the floats to sink and that would cause a fuel level above the setting when set by lid method.

[alan.barker]

I have a pair of old Webers and the machined landing where the Float Needles locate in the Covers is not the same. One is higher than the other and has a thick washer/packer to lower it to the same height as the other Weber. Maybe there are Float Valves with the brass bodies different heights. Are the height of the new Float Valve brass bodies the same height as the old. Have you compared new next to old
Alan

[Craven]

There are quite a few changes/modification to this area of the covers, I think they occur with changes to the fuel filter type built in the tower.
Best mod I?ve done is to modify valve seating and use the shaped plastic floats much better fuel level control, after all static level is one thing driving conditions, corners, bumps, uphill, downhill. Yes I know these conditions are designed in, BUT.

[Grizzly]

I've not had chance to have another play with it but drove it to work this morning and there is a marked improvement, i suspect with running it very rich the plugs are starting to play up as it has started to splutter pulling away gently (they are quite badly carboned up). I gave them a quick look at the plugs at lunch and i've now got a mid brown colour, i'll pick a fresh set up on the way home and see if that helps.