Spitfire Spitfire 1500, setup for single Weber carb

[jorg]

Hallo,
I am new here in this Forum and have a question about the carb setup for a 1977 1500 Midget. (In order to reach the Spitfire owners I posted at the Triumph-Forum too.)

Does anybody know what the basic setup for a single Weber DCOE 45 for a standard 1500 engine is? The car should mostly run under normal conditions with rpm between 1500-5000 with intention on maximum fuel economy and less power output above 6000 rpm and should have smoothe idle.

The following basic setups for a single Weber DCOE 45 I found on the internet:

Choke 33
Aux. Venturi 4.5
Main Jet 190
Emulsion Tube F9
Air Jet 175
Pump 40
Idler Jet 45F9
(Moss)

Choke 34
Aux. Venturi 3.5
Main Jet 150
Emulsion Tube F2
Air Jet 175
Pump 50
Idler Jet 55F8
Accel. pump (jet) 50
Ex.Valve 50

Choke 34
Aux. Venturi 4.5
Main Jet 145
Emulsion Tube F16
Air Jet 155
Pump 45
Idler Jet 55F8
Ex.Valve 40

Thanks
Jörg
Germany

 

[Alan_Myers]

Hi Jörg,

Welcome to the forum!

I think you will find that any info you gather on this will only be a starting point. Ideally, you should find a local Weber tuner and get the car on a dyno and/or exhaust gas analyzer to have the carb dialed in for your particular car. Spitfire data might not translate very well to an Midget installation, even though the basic engine configuration is the same. There are a lot of other possible variables (manifold design, valve sizes, exhaust system efficiency, emission controls, local tempertures and humidity, etc.) that effect any Weber DCOE installation.

Also, DCOE are not likely to give the best fuel economy. They are widely known to do just the opposite (some Weber downdraft carbs are more economy-oriented). One reason is the DCOE's accelerator pump, but you can play around with setting that up for a little improvement in fuel economy.

That said, I looked up to see what I could find in my Weber tuning manuals. The manuals I've got don't list the Mk 4 Midget, just the Mk 3 with the 1275 engine. They also don't list any Spitfire installations at all.

For the 1275 engine, the following is the recommended starting point:

45DCOE13
Choke 34
Aux. Venturi 3.5
Main jet 1.30
Emulsion tube: F2
Air correction jet: 1.75
Idle jet: 050 F9
Accel. pump jet: .50
Accel. pump inlet: .50
(needle valve: 2.25)

I notice this is nearly identical to your 2nd choice. Just judging from the additional engine size, I would think your 1st (Moss) choice might be closer.

Something to try is contacting Pierce Manifold here in Gilroy California (www.piercemanifolds.com). They are Weber specialists and might be able to give you more specifics.

Another possible source of info is Advanced Performance Technology, also in California, (www.aptfast.com), which is a Spitfire/1500 Midget specialist and offers Weber carb conversions.

Another Spitfire specialist is Performance Research Industries in Oregon (www.prirace.com), however their focus is not on Weber carbs, in general. They adapt other types of carbs for use on Spits.

Your goal to keep the car in "street" tune is certainly possible. I've run Weber DCOE on my TR4, primarily a street car, since the 1970s. One way to achieve street manners with DCOE is to keep to slightly smaller size chokes and then jetting to best accommodate those.

Hope this helps and that others jump in with some suggestions.

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[billspit]

I have no experince with the Weber on the Spitfire or Midget, but have read the single carb set up is not the best designed system. The two carb set up is better. I assume you have a higher compression engine than we would have in the US and possibly a more agressive cam. That is ggod. Otherwise bolting a weber onto a standard US spec car isn't likely to result in much pleasure. As Alan says, you really need a dyno to adjust the carb correctly.