View single post by Mark Rosenbaum
 Posted: 05-07-2005 10:09 pm
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Mark Rosenbaum

Joined: 03-12-2005
Location: Kingman, Arizona USA
Posts: 532
The 'choke' (actually a starting enrichment circuit) works by applying venturi-created vacuum through tubes to the fuel in the front carb's float bowl.  The amount of additional fuel provided is regulated by the size of the selected passages in the rotating disk that sits within the mechanism.  This means that raw fuel passes into the choke mechanism and thence to the venturis of the two carburetors.  Note that unlike conventional chokes, this method adds no restriction to the air intake path. 

If the rotating disk is installed incorrectly, the choke may not function, or may never shut off.  In the former case the car will be hard to start when cold.  In the latter case, you'll have an excessively rich mixture at all times.  This is another possible cause of the excess carbon in your exhaust.

If you didn't have a gasket between choke and carb body, any left-over fuel in the choke may have been the cause of the fuel dripping you noted.  If so, then all you need do is install the gasket.  If the old gasket doesn't work out, I can send you a left-over new one, or you can make one yourself from a piece of thin cardboard.

AFAIK the vacuum switch diaphragm is just plain unavailable and the price of a replacement vacuum switch is absurdly high.  I've made some attempts to come up with a means of replacing bad diaphragms but so far have not been successful.  Capping things off seems to be the only option in cases like yours.  Yours is the first switch I've heard of that has a gasket at the lower joint.

Jim Medland's comments about the temperature compensators are of course correct.  They have little effect save to slightly lean out the fuel-air mixture at idle once the engine warms up.  Basic functionality can be determined on the car by removing the plastic cover, applying hot air from a hair dryer, and seeing if the arm moves, but if re-calibration is ever needed they should be adjusted in pairs in a hot water bath.

The vacuum retard (not advance) capsule on the distributor should hold vacuum for much longer than just a few seconds, so I'm pretty sure yours is leaking.  You can just disconnect and plug the vacuum line leading to it -- but do save the parts in case you ever sell the car and it needs another emissions test.  As for the somewhat stiff wires inside the distributor, if these don't hinder the smooth operation of the centrifugal advance, coming or going, they are acceptable.  Problems in this area are often apparent when exercising the throttle while checking the timing with a timing light.

Strombergs, like SUs, can be re-bushed but this is rather costly and it's generally less expensive to buy a replacement carb through eBay.  However, with Strombergs the brass throttle shaft seems to suffer the majority of the wear.  Shaft life can sometimes be extended by polishing out any steps in the shaft, but this is limited as eventually the shaft seals will no longer fit, the shaft will wobble too much, or both.  Fortunately new shafts aren't too expensive.  Delta generally has both types in stock, and they should be available from a variety of other sources if Delta happens to be out.

Strombergs from Volvos work perfectly well in a JH, provided the correct mixture needle is installed; no other change is necessary.  In the JH-specific carb, the bowl is always vented directly to the air box.  In the Volvo carb, the extra linkage you mention operates a valve that vents or seals the float bowl depending on whether or not the throttle is open.  This is just another early emissions system which IIRC allowed Volvo to avoid using a carbon canister.  The whole thing can be converted over to the JH system if desired, but it's probably not worth bothering with.