Lotus Elan

Weber DCOE 40 151 Fuel Level

PostPost by: prezoom » Mon Jun 18, 2018 3:02 am

If the floats are able to rock on the pin, the bent part of the float, where the pin fits through, must be tightened up to the point they will still rotate but not rock side to side. Bit of a fussy job, but to set the floats correctly, the floats must not rock side to side. As far as the idle jet selection goes, Google up the list of all the idle jets that are available. The permutations are almost beyond belief. The simple ones have one fuel opening and one air opening. Some have two 2 air openings, and the internal bores can vary in diameter and in depth, or a combination of both. It's enough to drive one to drink even more. I went through F6, F8, F9, F12, and any number of fuel sizes to get the 2L Zetec to run without any hesitation or stumble, yet still deliver 32mpg (US) at 70+mph, with 152G's, with five 5 progression holes. Not FI, but I am mired in yestertech.
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PostPost by: alfadave » Tue Jun 19, 2018 3:51 pm

With Eric's help I adjusted the float tabs/arms to get 41.5mm from the rim to fuel level.

This ended with the float/cover clearances being 6/18mm

So , a big difference from Webcons figures.

Car is running fine.
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PostPost by: alfadave » Wed Oct 10, 2018 6:21 am

I'm still fiddling with fuel levels here.
The car was running fine.......but after 30 miles or so, the plugs are sooting up.

I discovered I had a Haynes Weber Carb Manual from years back.
The diagrammatic drawing of the DCOE carb on normal phase on p.144 shows the fuel level well below the aux venturi passage.
There is no scale, but the distance below looks more than the diam of the main emulsion tube drilling........a lot more than the 2mm mentioned by Keith Frank.

2mm seems very close to the venturi passage.........fuel could slosh on cornering?
And if the fuel level is set with the emulsion tube out, will the level raise when it is replaced?

Craven, earlier in this thread mentioned 5-6mm below the passage.......I'm erring towards that school of thought.
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PostPost by: Craven » Wed Oct 10, 2018 4:04 pm

There is not a definitive measurement for level below the spray nozzle bore, in sports car applications best performance is obtained by setting the level close to the bottom edge BUT you then encounter unwanted/spill over fuel emissions. If set to low poor acceleration, idle speed and part-load/low RPM. In my experience fuel level stability is fundamental, you can play forever with jets, chokes etc. you are just wasting your time until a stable level is established, check fuel delivery pressure and condition of needle valve. Never tried it but moving down to a 150 may help if stability is the problem.
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PostPost by: mbell » Wed Oct 10, 2018 6:32 pm

I second checking the needle valve and fuel pressure.

The float level is just another calibration parameter on the webers. The main circuit uses a venturi to create a low pressure effect that "sucks" the fuel up through the jet and up the jet holder down into the carb throat. The lower the fuel level requires a lower pressure to lift the fuel enough. To generate the lower pressure region requires a higher/faster air flow through the venturi. So adjusting the fuel level effects the point that the main circuits start to flow fuel.

Weber often have a flat spot as they transition between the two circuits, raising the fuel level means the main circuit kicks in earlier that can richen the mixture during transition and avoid the stumble.

Of course if the fuel level is set to high or fluctuates too much fuel can run through the carbs and straight down the throat giving a very rich mixture.
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: alfadave » Wed Oct 10, 2018 6:42 pm

I've replaced the needle valves.
Fuel pump is a new mechanical type bolted to the block.
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PostPost by: Grizzly » Wed Oct 10, 2018 11:46 pm

From recent events with my own carbs i'd suggest sticking an endoscope down the venturi and watch the pump jet operation (you can also watch the venturi for any over flow due to the fuel level being too high), i spent ages polishing the demand valve ball and seat to seal 100% but when i raised the fuel level to 25mm they all started to siphon again.

The sure fire way of checking this is to remove the spill valve and rev the engine a couple of times while watching the jets, this was the time i could see mine constantly dripping.

The Pump jets are the bane of my existence just at the moment, they look like their working fine but the difference between running with the Pump piston removed and fully assembled is quite dramatic on the air fuel ratio meter (driving without using aggressive throttle as to not need/use the pump jets)
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PostPost by: Andy8421 » Thu Oct 11, 2018 3:32 am

Grizzly,

I have a vague recollection that at high airflow rates, the depression across the accelerator pump jet causes the balls to lift off their seats to allow high speed enrichment.

Is this the effect you are seeing?
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PostPost by: Grizzly » Thu Oct 11, 2018 6:24 am

Not really, what seems to be happening is a siphon effect once the pump jet has been activated. It's so minor all i can see is a slight drip on the end of the pump jet when it's running but when i take the spill valve out it's highlighted, Remove the the pump circuit piston (so the Pump jets don't work at all) and there is a big difference to the AFR just sat stationery (idling and low rpm especially)


BTW, check the return hole in the Spill jet too...... if your running a stock set up and that gets blocked you get allot more fuel / the pump jets become more sensitive (supplying fuel when there is small amounts of throttle / cruising completely shafting your MPG figures) so you get pooling of neat fuel that hits the throttle plates and drops to the floor of the venturi / inlet runner also giving a lower AFR across the board.

Some thing else i noticed was if you set your Idle mixture up by Colour tune to just going orange (as the instructions tell you) your way too rich around 10afr, going off my AFR meter 12.5afr on idle at 1000rpm as roughly when you see the solid blue with the slightest flicker of orange, i can still make it idle really well when orange /10 AFR but i get sooty plugs even on BP5ES plugs when left to idle for a few mins.

One of the best and worse things i ever did fitting a AFR meter........ :roll:

Yes refitting the main jet does raise the fuel level but it's only very slightly, i have my fuel level set to 25mm and i can refit one main jet without seeing any fuel dropping into the venturi so i guess the amount displaced by the jet assembly doesn't raise the total fuel level in the carb more than 1-2mm, two main jets at the same time on the other hand may well overflow.
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PostPost by: alan.barker » Thu Oct 11, 2018 12:02 pm

alfadave wrote:I've replaced the needle valves.
Fuel pump is a new mechanical type bolted to the block.

Is the Mechanical Pump an all metal one or original with glass Dome.
If it'a an all metal replacement Pump lots of them produce too much pressure and cause flooding :wink:
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PostPost by: alfadave » Thu Oct 11, 2018 3:33 pm

Its an all metal replacement fuel pump
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PostPost by: alan.barker » Thu Oct 11, 2018 5:41 pm

Imho you need to check the pressure. I have tried one of those in the past and had to fit a Pressure Regulator :wink:
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PostPost by: jk952 » Fri Oct 12, 2018 11:52 pm

I thought I read somewhere there was a typo error in the 25 mm reference for float height?; but in my limited experience that puts the level too high, (and above the channel to the transition holes), the stock levels are with the floats essentially horizontal when floating in fuel. I believe the 151 float with the fuel at about at the parting line of the plastic, can’t accesss the carb easily at the moment to see. The brass are at midpoint, but note the 151 plastic float pivot point is different as top castings are different in respect to the pivot point. I have floated both the brass and plastic in fuel to see where the fuel sits when floating.
... 2 cents worth to confuse the issue... :D
happy to be corrected with accurate info
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PostPost by: mbell » Sat Oct 13, 2018 12:24 am

The 25mm is from the top of the jet holder to the fuel level. Not between floats and cover as standard Weber instructions state.

On mine 25mm down the jet holder puts the fuel level 1mm below the passage to the throat.
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: jk952 » Sat Oct 13, 2018 2:16 am

I understand the difference: I should have said more specifically fuel level for setting float height...
pict. is distance to top of passageway from casting, about 27 mm.

This is an older 40 dcoe body but same re that, odd different from yours...

0623eaf3-84a6-4f19-b926-b30f8890a58a.jpeg and


This second pict. is a wire I have used on the 151’s to check if the plastic float is actually floating in position ( eg if fuel evap.): so from the top of the carb. cover casting to the top of the plastic floats, fits in by just removing the cap. over the jets. (obviously though the number looks similar a different measurment)

dff30b56-5a66-4590-89ba-a7a45ba7cce6.jpeg and
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