| engine | -- 12-08-2012 @ 11:48 AM |
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I have a 8 cm engine with the 2 barrel carb.On a trip I started to get a surging while driving down the road,I thought it may be a fuel pump or the accelerator pump.I took out the pump and it is a leather one with a few score marks on the side also the rod that it is connected to has scoring as well on the side that is inside the carb.I was wanting to know if anyone know if this is the problem. Thanks
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| carcrazy | -- 12-08-2012 @ 12:23 PM |
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Surging can be caused by several items. If it is a road load surge experienced while driving down the road at a steady speed, neither accelerating nor decelerating, it is most likely caused by a lean air/fuel mixture. Intake manifold leaks, partial blockages or leaks in the fuel lines, a plugged gas tank filler cap, or contaminated fuel could cause a lean mixture. Surging at low speeds could also be caused by burnt or sticking exhaust valves. Hope this is helpful. Problems with the carburetor accelerator pump won't cause surging but will cause a hesitation on acceleration.
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| supereal | -- 12-08-2012 @ 2:29 PM |
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I would suspect a bad distributor advance diaphragm, or a vacuum leak in the line leading to the distributor, which doesn't have a mechanical advance, only vacuum. Surging usually isn't a carb problem unless the float is sticking or dropping.
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| Stroker | -- 12-08-2012 @ 4:50 PM |
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Just to add to Supereal's & Carcrazy's good advice, the 8CM-8BA distributor is unique. The vacuum signal is actually sourced at the carb venturi. Sometimes people assume that vacuum is "vacuum", and assume that you can hook this distributor to any manifold vacuum source. In this case (48 truck-53 everything), the system was designed around venturi vacuum, not manifold vacuum. It is possible that at some point in history, manifold vacuum has been substituted, basically messing-up the designed advance curve. The attached article by the late Barney Navarro, while directed at people with aftermarket carbs, explains the above referenced ignition's distaste for "manifold vacuum".
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| 51f1 | -- 12-09-2012 @ 7:07 AM |
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Very good article. Thanks. A small historical correction: The Loadomatic distributor (using only vacuum advance) was used on Ford 8RT engines (trucks) beginning in 1948. Richard
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| Stroker | -- 12-09-2012 @ 5:44 PM |
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51f1: You will note that I used the 48 truck date, but in the case of Barney's tech. article, he's dead, so I can't correct him.
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