By Charlie Seabrook

In offering a few suggestions to help Lotus owners who are using Weber carbs on the 907 engine, let me first say that carburetion is something of an art - what works for some cars may not work for others.

I drove my 1978 Eclat from new for about one year prior to installing Webers. During this time, I installed a fuel flow meter, which measured gasoline flow down to 1/100^th of a gallon, and I got the ignition system in good shape, with a reworked distributor advance, a multiple spark discharge ignition system and Monel spark plug wires. This 4 speed car came with the wrong axle ratio, so I switched from 4.10 to 3.77 ring and pinion. I also used rather larger rear tires - 235/60-14.

The baseline gas mileage figures with Zenith Stromberg carbs was 28-30 MPG on short trips and 33-34 MPG on long trips at 3500-3700 RPM. When keeping down to 3000 RPM or 58 MPH, the mileage would average 35 on long trips. I often got instant readings of up to 41 MPG - at steady speed, with no hills, no wind, the engine well warmed up, fuel-efficient oils, plenty of tire pressure, etc. However, the above figures are tank averages.

After I installed a set of 45DCOE9 Webers taken from by Aston Martin (the DB6 got a new set of 48DCOEs), information on jets and venturi settings was difficult to come by. Most people I called said, "Buy Webers from us, and we will install the correct jets, emulsion tubes, etc."

So, I stopped by my friendly Lotus dealer, took apart a new Weber setup for the 907, and used those jet settings as a starting point. What a disappointment! The Lotus ran like a tiger - really a fantastic performance increase over the Strombergs - but the trip mileage was on 15.5 MPG! Despite many main jet and air correction jet changes, I could not get decent mileage and performance using F16 emulsion tubes.

As any student of Webers probably knows, there are so many variables of jet settings possible that your average eight digit calculator does not have the capacity to count them. I make a lot of fairly long trips, so I filled a large coffee can with sets of emulsion tubes, main jets and air correction jets. In the process, I discovered a lot. One thing is impossible; you cannot get all the performance and top mileage with one group of settings.

Here are the settings I finally ended up with:

Emulsion tubes     F2
Fuel Pressure     3.5 psi
Chokes     35mm
Pump Jet     50
Idle Jet     50F9
Main Jet     120
Air Correction     180
Auxiliary Venturi     4.5
Pump Discharge     #40
Accelerator Pump Spring     light
Needle Valve     175
Float Level     7 mm
And a short rod on the accelerator pump

If gas mileage is really important, the 45F8 idle jet can be used. Idle jets on Webers control the mixture from idle all the way up to and beyond 4000 RPM. With this jet, you get some slight lean surge and a definite hesitation when opening the throttle at 3000-3500 RPM. The 45F8 saved me about 2 MPG on long trips over the 50F9. If you want better off-idle response, use 55 F8 idle jets. Again, you will lose another mile or two per gallon.

For racing or high performance work, increase the main jet to 125 or 130 and decrease the air correction jet to 170, 160, 150, 140 or even as low as 135.

This high speed response improves as the Air jet is reduced, but you pay for it in gas mileage. With maximum performance jets, the engine pulls almost instantly to 7200 RPM in every gear, including 4^th, and I don't think anyone can expect any more performance than this from a 2 liter engine.

For normal daily driving, I use the final settings listed above. Gas mileage runs about 2 MPG less than with the Strombergs: 26-28 on short trips, such as the ten miles from home to work, 31-32 on long trips, and a best of 33.5 under ideal conditions. On one extended trip to the West Coast, through the Colorado Rockies and back through Texas, I averaged 29.5 MG - while using the air conditioner a great deal and enough full throttle to make the Rockies seem as flat as Texas.

On the Eclat, Webers provide a couple of additional advantages. The car starts from cold much better, and although I hooked up both chokes to the original choke cable, choking is required only on the coldest of days. The torque of the engine is greatly improved, even as low as 2000 RPM - and at 2500, the engine pulls like a bear, even in 4^th gear. And engine run-on is completely eliminated.