Lotus “Twin Cam” dual Stromberg to Weber DGV conversion.

By David Maughan

I’ve owned several British cars over the years, and had the fortune of some of them having Zenith Stromberg carburetors. My current “toy” is a 1974 Lotus Europa Twin Cam Special. I bought this car a few years back, completely original, and having only covered about 16,000 miles. I drove the car for a while on the Zenith Strombergs, but was never very happy with them. Sure, after a rebuild and balance job it would run fine for a while, but my experience is they lose their tune quickly, and besides, I really don’t care for rebuilding them every 10,000 miles or so.

Around Christmas time 2004 I was sitting at work, and started to think about cars I’ve previously owned. One such car was a 1979 Ford Capri 2.0S. I owned this car while living in England. It was a fantastic car. It had a 2 liter “Pinto” engine that made about 110BHP. It was at that point that I thought “what carburetor did that have”. It was a twin choke Weber 32/36 (DGV). The Capri never let me down, never lost it’s tune, and the roar from the engine when the second choke of the Weber opened was fantastic. This left me thinking… “I wonder if there is a way to put a Weber DGV on the Lotus?”. At this point, I made a few phone calls. I called a few places and asked about alternate carb options for my Twink. Only one place (DBE) had an option for me, and it would cost around $4000 for machine my head to accept twin side draft Webers, and supply all the parts for the conversion. This was way too much money, plus I want to keep my car as original as possible, so one day in the unlikely event that I decided to return it to the Strombergs I could. I mentioned to DBE that I would like to use a DGV… Their answer “I will never work”. WRONG ANSWER!

For people unfamiliar with the Weber DGV carburetor. The DGV is a twin choke (two barrel) progressive downdraft carb, that has been in production for years. It has been used by many manufacturers as original equipment on cars ranging from Alfa’s to Fords. DGV’s can be bought used for peanuts, and are still in production. Parts are cheep and plentiful.

Back to the story.. After pondering at work about a possible carb swap on the Lotus, I went home that evening and started measuring the available space around the intake side of the engine in the Lotus. I also removed the Strombergs and measured their mounting pattern, mounting angle, etc. I then went online and searched the dimensions of the DGV, including the carb’s base mounting pattern. At work the next day (You probably noticed here that I occasionally get a little free time at work) I fired up AutoCAD and started drawing. I played with designs on and off for about two weeks, until I finally came up with a crude design that I felt would be a good prototype. At this point, I sent the design off to Krem Engineering and had Al make me up one out of scrap aluminum. This is basically what I got back (Picture was taken after it had been mocked up and tested, so it’s a little dirty).

This design proved to be pretty good. I showed that it fit in the engine compartment, and the throttle cable, and fuel lines reached. Below are a couple of pictures of the first test fit.

Once I was happy with the fitment and location of the manifold I moved onto the carburetor mounting, throttle linkage, choke linkage, and the air filter. The picture below show the carb on the manifold. Note the throttle lever. This is a modified Toyota Camry circa late ‘80’s piece. Underneath the carb is a 1/8” spacer/insulator.

With this assembly in place, I could verify that it was possible to close the engine cover. So, it was time to mount the carb to the manifold and hook it all up. Unfortunately in my excitement, I didn’t take a picture of the prototype all hooked up.

With everything hooked up, it was time to see if she would run. After a couple of dozen spins of the starter the float filled and she started! Remember, this is a crude manifold (no port matching, large diameter tubing, and a square “plenum”) also, the carb is straight out of the box. With the car running and warm, I set the idle and idle mixture to something close.

The first test drive was taken the following evening, and it was quite funny. The car idled great, and revved fine when no load was present. As soon as I attempted to drive the car, shortcomings in the design became very obvious. The car lurched and spluttered along, only happy a certain RPM’s, but it did run, and it was almost drivable. At this point, I was forced to push the a car aside for a while as I had taken a new job and was being moved by my new company. So, development of the DGV Twink stopped. After the move was complete, I started work on the car again. I took the entire assembly off, and started doing a little port matching on the manifold. This made the car drivable, but it still loaded up at certain throttle positions and RPM’s. I was happy though that the design had proven itself, and the DGV right out of the box seemed to work well with the Twink.

The design was proven, so it was now time to make a more permanent solution. The recent move from Tampa Florida to the Sarasota Florida area put me very close to Steve at Twin Cam Sports Cars in Sarasota. I called up Steve, and discussed my car with him. We agreed for me to deliver the car to him, and he would follow my design of manifold using my DGV carb, but build a more permanent solution. Two weeks after delivering the car to Steve, he called me and said come and drive it. Steve had built a manifold that allowed the air/fuel mixture to flow nicely, and stay atomized. (My square plenum was causing fuel puddeling.). I drove the car and it was excellent. Smooth idle, excellent power delivery, and when the second choke opened, it was fast! Steve and I both agreed that a horsepower increase was evident over the Strombergs.

Below is a picture of the finished assembly. The original design had the throttle cable coming across the engine which proved bad as it melted the throttle cable. After fruitlessly trying to insulate the throttle cable, I realized it was possible to rotate the carb on the manifold 180 degrees, and run the throttle cable under the car away from the heat. This also placed the choke actuation in perfect position for the stock choke cable.

So, a DGV does work on a Twink, it runs great, makes good power, and can be returned to Strombergs if required. Also, this carb is easily good for 100,000 miles before needing a rebuild and there is no fire risk as with the plastic fuel fittings on the Strombergs.

So much for “it will never work”.

Thanks go out to Al Krem of Krem Engineering, and Steve at Twin Cam Sports Cars.

David Maughan – v846@yahoo.com

Krem Engineering 814-724-4806

Twin Cam Sports Cars 941-923-0024

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