Double carb vs. single carb

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Double carb vs. single carb

Post by Chrstncloete »

Hi Guys,

I bought a '75 autovilla 2.0l for my Dad and I am in the pocess of getting it back on the road.

I need some advice regarding the carb setup; do I stick with the current dual carb setup or do I convert it to a single carb for the sake of simplicity and reliability?

Also which would give better fuel economy?



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Re: Double carb vs. single carb

Post by Tony Z »

dual carb is smoother and runs better when setup properly
dual carb is lighter on fuel when setup properly
your dual carb is 39 years old... how is that unreliable? Service it properly and rebuild it if needed and it will be good for another long while.

Single carb is simpler but will never be as good
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Re: Double carb vs. single carb

Post by Dawie »

With any carb setup, vaporization of the fuel is critical, especially when good fuel economy is expected. Only the "misty" part of the mixture can burn completely in the split second time of the power stroke. Fuel droplets does not burn completely, they causes carbon build-up and washes the oil film from the cylinders.

Even when the carb sits right next to the intake, this is not ideal. Many conventional inline carbed engines still had an exhaust "hot spot" below the carb for fuel economy reasons.

Vw used exhaust heat on their single carb type 1 engine's manifolds. The 1900 watercooled engine used an electric heater and hot water to heat the single carb's manifold.

Remember to keep your intake air pre-heater system operational if fuel economy is important to you. The diverter valve will automatically divert back to cold air during full throttle operation.

By the way, never use 2 individual aftermarket aircleaners on top of the 34PDSIT carbs, unless you plan to have that carbs drasically re-jetted on a dyno. The resonating long ducting length to the standard aircleaner setup causes enrichment, especially where one carb feeds only 2 cylinders. Removing this ducting will result in lean mixtures at full throttle, causing loss of power and a blown engine.

Even in a type-1 1600 combi application, VW dropped the main jet by 5 points (relative to a beetle application). This is because of the richening effects caused by pulsing air in the long ducting and not "air cleaner element restriction".

When using a single carb on an unheated central manifold, jetting has to be rich to prevent flat spots. Doing this will be a step backwards.
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Re: Double carb vs. single carb

Post by Sambabus »

Super interesting.

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