Lotus Elan and Lotus Elan Plus 2 Forums

Hi all.

Does anyone know what size bypass holes were used in the 050 Spill valves fitted to Elan Sprints Weber 40 Dcoe?

Grizzly wrote:Hi all.

Does anyone know what size bypass holes were used in the 050 Spill valves fitted to Elan Sprints Weber 40 Dcoe?

size is in 1/100th mm, so 50 is 0.5mm diameter

Isn't the size .050" which is about 1.2mm? (off the top of my head) i'm fairly sure 60's/early 70's Webers were still imperial but i could be wrong??

Grizzly wrote:Isn't the size .050" which is about 1.2mm? (off the top of my head) i'm fairly sure 60's/early 70's Webers were still imperial but i could be wrong??

Webers from Bologna Italy would not be imperial I believe - I now will have to double check on sizing code later tonight as the top of my head tends to be a bit of a mess of late...

Italian Webers were all metric. Even modern Webers manufactured in other countries are all metric. It would be a huge stretch to presume any stated jet size or dimension was in inches.

Regards,
Tim Engel

I think i might have confused myself, so it's the bypass hole in the side that is 0.5mm not the size of the hole in the front.

That makes more sense..... so the Pump jet size denotes the amount of fuel delivered and the spill valve bypass hole determines the duration of the shot.

Does that sound about right? i was thinking the .5mm was the valve hole size so was confused why it was quite a lot bigger than that.

That might help me quite a bit, I've noticed my webers have 00 spill valves and i'm getting black smoke under hard acceleration which is where my question came from.

Chris,

If you have the patience, join sidedraft central, which is a web site run by Keith Franck. Keith is an American living in the Sanfranscisco area, he is a retired physicist, and has spent ages improving Webber carburettors.

Richard Hawkins

Grizzly wrote:I think i might have confused myself, so it's the bypass hole in the side that is 0.5mm not the size of the hole in the front.

That makes more sense..... so the Pump jet size denotes the amount of fuel delivered and the spill valve bypass hole determines the duration of the shot.

Does that sound about right? i was thinking the .5mm was the valve hole size so was confused why it was quite a lot bigger than that.

That might help me quite a bit, I've noticed my webers have 00 spill valves and i'm getting black smoke under hard acceleration which is where my question came from.

I would rather say that the pump jet determines the duration of the shot, and the spill valve the amount delivered (though that is also dependent on the pump jet) : there is a fixed amount a fuel that will be pressed by the enrichment spring when required, and during the shot part of the fuel will go to the cylinder, part of it will return to the bowl (according to a ratio in relation to the ratio pump jet / spill valve).

Early on, I found that playing with the size of the by pass hole can increase the car's gas mileage. Rather than have more fuel that is needed by the engine during the acceleration faze, excess fuel can be by passed back into the float bowl. This is especially true during driving where one is on and off the throttle frequently as on curvy roads, or heavy traffic situations, where the accelerator pump is in constant action. It took some time to find the sweet spot, balancing pump jet and idle jet size to keep from getting the dreaded flat spot. While not perfect on my S2, the Plus2 with 152G's, and 5 progression holes, the Zetec runs as smooth as silk.

I bought a pair of 50 spill valves today, strangely they had .4mm holes which is a bit odd...... i've taken them out to .5mm though and fitted them.

First impressions is 80% of the black smoke has gone and it's considerably smoother / pump jest are less sensitive (i was getting the pump jets trying to spray fuel when cruising which wasn't doing anything for the MPG).

Looking at my AFR maybe i could go another size bigger but i might leave it now until i go with the Mr Franck Idle and E-tube set up, then spend a bit of time dialing it in.

Thanks for the help.