Sticking Choke on HD-8 carburetors

By Eric Grunden

Originally published in the Austin-Healey Magazine, January 1997


Here are some additional thoughts on the recent Internet conversations regarding the problem of chokes sticking on the Healey HD-8 carbs. (Figure 1)


The problem could be dirty or worn, primary or secondary choke cables, jet (#8) and jet bearing (#19) not centered, a bent metering needle (#22), a worn or broken jet return spring (#21), galled or dirty jet and jet bearing, or galled or dirty cam shoe and rod (#26).


If you have eliminated all of the above and are still having problems (e.g. jet returns fully but engine still idles too fast), the problem may be in the jet housing assembly.


The jet return spring (#21) will only return the jet and fast idle cam until the mixture adjustment screw (#24) contacts its stop.

The fast idle cam, cam shoe, and rod then rely on the small spring (#27) at the top of the rod (#26) to return the cam, cam shoe and rod to the slow running position. Simply adding an auxiliary spring to the jet hand control lever (#A) may cure the problem but can cause the primary choke cable to be very hard to pull.


The most often overlooked problem is the cam spindle itself (#B). Servicing this will require partially disassembling the carburetors (best done by taking them off the car). Remove the four screws securing the float bowl to the carb body, and remove the jet housing assembly (#23). Using a proper size punch, drive out the tapered pins securing the cam and the center lever, taking care not to bend the cam spindle. (If doing two carbs, work on one jet housing assembly at a time using the other as a reference to avoid confusion when reassembling the carbs.) The cam spindle can now be withdrawn. Clean the cam spindle with a fine emery cloth or steel wool. Clean the cam spindle bores and jet actuating lever bores thoroughly. Inspect the bottom portion of the jet actuating lever fork (#C) that contacts the top of the jet cup. If any sharp edges are found, carefully file them until the contact surface is smooth and free of any burrs. The cam spindle should now rotate freely in the bores with no tight spots. Inspect the cam itself for smoothness and sand or file as necessary. Reassemble the jet housing and then the carb itself.


Those with HD6s should also consider cleaning the cam spindle during a carburetor overhaul.


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