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Help Needed With Twin Choke Carburettor
Please
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Posted By : Stephen Coates, 20-Aug-2006,
03:07pm
Hi, I wanted to check the exhaust emissions on my 79 VW Camper van with a Gunson Gas Tester. The van has a twin choke carburettor fitted and I would like
to adjust the idle speed, as it currently only idles at around 650 rpm. The problem is I am not sure which screw (there are two of them) is the idle screw
and which is the mixture screw. There is a long screw very close to the throttle linkage, while the other screw is located further away in the centre of
the carburettor body. The exhaust emissions CO currently reads 1.8 % and I am keen not to turn the wrong screw and upset the setting. Any help would be
gratefully received. Many thanks Steve.
Help Needed With Twin Choke Carburettor Please
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Posted By : Chris Taylor, 20-Aug-2006,
03:48pm
Can only suggest you get a manual for the vehicle concerned. Doesn't look anything like any carb used on a Triumph.
If the idle speed is set by the carb butterfly position, you should be able to identify a throttle stop position screw by tracing the accelerator
linkage and seeing what moves when someone presses the pedal, and what limits its travel when the foot is take off the pedal.
If however the idle speed is set by a bypass screw or idle circuit, then you will need to find the correct screw, which may indeed look like a mixture
adjustment screw.
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Posted By : Peter and Mick Lewis,
21-Aug-2006, 09:55am
idle srew is on the right of photo and mixture is the one on the left in the cast body level with the throttle plate if the carb had a air bypass
it would normally be much larger diameter and halfway up the barrel body, so set idle speed with screw on linkage to specified rpm. then adjust
mixture screw to get best sweetest running, then screw it in to drop idle by 50 rpm you are then at the weakest end of its best running point ,,
assume throttle spindles are not worn as these suck air.
if its a twin choke the 2nd barrel throttle plate is pre set and should be just closed, some need a very small opening just to stop sticking and
fuel building up if its open to far it affects idle speed this barrel does not have a idle circuit to adust.
dont forget any mixture adjustments you make only affect the idle circuit and not the general running settings which is controlled by the fixed jet
circuits,,,if the idle is too fast you open the throttle plate beyond the small idle orifice which is next to the edge of the plate and you will
not get any reaction
with the mixture screw so slow idle is better than too fast ... peter