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Mon Sep 22, 2003 5:02 am

Could someone explain to me what the dashpot's function is ( on the carburetor ) ?

Also, do the auto chokes need to be adjusted depending on the season (eg winter versus summer) ?

Trying to understand what all the bits of the carb do.
Thanks

Mon Sep 22, 2003 6:37 am

Diito on the dashpot dilemma.

Mon Sep 22, 2003 6:53 pm

The dashpot on a dual carb bus is there for two reasons.
1) It keeps the engine from stalling if you close the throttle too quickly.
2) It stops you from polluting the air during overrich conditions when you are decelerating. When you downshift and use the engine as a brake to slow you down i.e. a traffic light; the throttle will be fully closed, manifold vacuum will be very high, the engine will be sucking raw fuel thru the idle circuit, but you will have no clean going into the intake to complete the burn. The dashpot is there to keep the throttle open slightly to allow clean air in. The throttle will slowly close, hopefully by the time you have reached idle speed.

Wed Sep 24, 2003 9:30 pm

Thanks, Karl
So the dashpot is some kind of damper or shock absorber?
Do you have any ideas on the autochoke question?
Terry

Sun Sep 28, 2003 8:47 pm

Tezza wrote: Thanks, Karl
So the dashpot is some kind of damper or shock absorber?
Do you have any ideas on the autochoke question?
Terry

On the '72-4 dual carb buses, the dashpot (a "pneumatic door closer", by the way) only comes into play for a couple of seconds when the accelerator is released suddenly. It does not relate to off-throttle over-run conditions, because the OEM egr and air pump systems ensure properly lean conditions. The dashpot was actually only to reduce emissions from accelerator pump injections that had no time to burn with what-should-have-been open throttle plates because of the driver changing his mind and shutting them.
The dashpot has very little effect on driveability with a correctly adjusted engine. If you ever have stalling or surging from snapping the throttles, you most certainly have mixture/speed/timing issues to hunt down.
The chokes do not need seasonal adjustments, and I can guarantee you this anyway, they will always be slightly annoying. The most usual symptom of these chokes is a fast idle greeting you after a quick trip into the store on a cool day. The engine internals will be still warm, the ambient engine compartment temperature will be cool, the chokes start closing, and presto, an idiotic fast idle for no good reason. If you adjust the chokes to get rid of this symptom, you will lose that beautiful *cold* start performance. When I have a warm engine on a cold day, I just turn on the ignition for a couple of minutes before I start the car when I get back from my little dash into the store. This gives the choke heaters a head start, I might have a fast idle while trolling in the parking lot, but it'll settle down by the time I get to the first light or stop sign.
Colin