Weber DCOE 40 - float height question

[Lo100469]

Good morning,

i own a TR4 A that came with Webers.  I had the engine and the carbs rebuilt and everything runs as it should except 2 small issues.

1 - idle goes up to 1500rpm from time to time (suspect some fuel find its way at idle)

2 - after the last run (i have maybe 250 miles post rebuilt - weather was quite hot Saturday like 26 degrees) i did hear the infamous pcchht of fuel hitting a hot object after shutting down the engine, and did see that the front carbs was leaking at the inlet manifold for a minute or 2, no big leak just a drop every 5 seconds.

I suspect fuel height is too high in the carbs, i did read that a new fuel valve settles and that you have to readjust float height after a few hours of running.

Now does everyone have a starting point a fuel height and float height on those DCOE 40?  I do have the plastic ones and did read 14mm.  Also the normal fuel height is 25mm but some recommend 29mm (from the top of the main jet base to the fuel).  Also i guess fuel height matters and float adjustment is just a way to get to the right number?

Thanks for your support

Kind regards,

Laurent

[BlueTR3A-5EKT]

Terri Ann’s info is in the link

http://www.tr3a.info/WeberDCOEinfo.htm
 
What we do know is TR engines need the float set lower than the super smooth moderns like Ford et al as they do shake about causing frothing etc.

 

[Lo100469]

Hi Peter,

Thanks, very interesting reading, i can see the 8.5mm for a brass floater.  This is the number i wanted to check for the plastic one, i could find 14mm in some places.

If you lower that number, you make the fuel level higher by the same amount.  When you say a TR engine requires the float set lower you mean the fuel level?

kind regards,

Laurent

[BlueTR3A-5EKT]

1 hour ago, Lo100469 said:

Hi Peter,

Thanks, very interesting reading, i can see the 8.5mm for a brass floater.  This is the number i wanted to check for the plastic one, i could find 14mm in some places.

If you lower that number, you make the fuel level higher by the same amount.  When you say a TR engine requires the float set lower you mean the fuel level?

kind regards,

Laurent

Yes lowered fuel level to stop frothing and overflowing, is what I was told years ago by the man operating the rolling road in Mitcham.   They had a dyno with a red line at 300 BHP so there was not going to be an issue for my friends TR2 on Webers.

[Tom Fremont]

I was told many years ago by Darryl Uprichard of Racetorations that they set all their floats to 5mm. ( This must only apply to the brass type. )

I did this with my triples and it made a critical difference.

Later I got a clear gauge to measure the fuel depth from the top of the well ( where the main tube screws in - remove to check ). I found that 5mm with 3-ring vintage Italian 40DCOE-18s this gives 27mm depth. Oddly, older 40DCOE-18s with brass shafts on another engine gives 27mm with a setting of 8mm. Such depth is the key to when the main systems enters the game, the higher the level the lower the rpm. IMO 25mm is the absolute highest setting and not necessary for TRs and I would avoid going that high for the reason Laurent seems to have with his.

Regardless of float type I suggest attaining 27 or 28mm fuel level, equal between carbs. For plastic floats this may correspond to 12mm but do confirm.

Tom

[Lo100469]

thanks Tom,

i will aim for something like 27mm and report back the necessary plastic float height.

kind regards,

Laurent

[Lo100469]

Quick update:

I measured float height to get to 25mm (from main jet deck to fuel level)  cold (priming the fuel pump manually).  I had to add 1mm to the front carb that was leaking, this is close to 12mm at the tip.  Don’t try to ply the float lever without removing it, you will damage the valve (ask me how i know).

After a drive yesterday the front carb is still dripping after i shut down the engine. So i measured the fuel level just after switching off the engine and the fuel level is too high when hot, like 22mm to fuel level, 25 mm is standard, some go to 27mm (remove the main jet and measure from the deck down to fuel level).

Next steps:

- i did read that the DCOE front cover (towards the engine between the barrels) of the Weber should be vented.  There is a hole in the middle of it in most spare ones, mine does not have one, vapor could build up there and leak after switch off.  I will replace the covers and gaskets with ones with holes.

- i will add another 2mm to float height to lower the fuel level at around 25mm

- also installation of a heat shield below the carbs and an inline fuel filter to lower the fuel pressure a bit (even if I’m on the AC mechanical fuel pump that should not be pushing too much pressure).  I will have to remove the carbs which is taking time but does not seem overly complicated.  

Cheers

Laurent