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Posted By Discussion Topic: soot at carburetor base -- page: 1 2     fordmerc 11-10-2010 @ 9:58 AM reply profile send p.m. New Member Posts: 180 Joined: Oct 2009 Black soot is present at the carburetor base and intake manifold in the small hole between the two barrels. Although I don't understand the hole's purpose it seems wrong to have any soot on the intake side (?) This is a '39 engine and I removed the carb because the engine runs roughly. Do I have a problem? supereal 11-10-2010 @ 12:26 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 Check the gasket between the carb and the manifold for voids. Often there is some soot-like deposits where the exhaust channel under the carb burns the paint on the manifold, but there shouldn't be any holes that reach into the manifold, itself unless it was tapped for some accessory. If there is a vacuum leak, it would account for the rough running engine. I'd put in a new gasket, in any case. fordmerc 11-10-2010 @ 2:41 PM reply profile send p.m. New Member Posts: 180 Joined: Oct 2009 The gasket "looks" intact. What is the purpose of that hole/channel in the manifold and carb. Can it be plugged? I still can't imagine exhaust soot in the intake manifold unless that hole connects to the exhaust. (This is not just burned paint) supereal 11-11-2010 @ 7:55 AM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 Perhaps you can post a picture of the area so we can see the hole. If it enters the exhaust channel, I'd suspect you could see, feel, or hear a leak. If it is an irregular hole, it could be a "burn thru" of a sand pit fault in the casting. fordmerc 11-11-2010 @ 2:00 PM reply profile send p.m. New Member Posts: 180 Joined: Oct 2009 Courage conquers ignorance. Body of carb removed from base. The economizer by-pass valve is corroded and black. So the little "hole" goes from manifold through carb base to the chamber for the power valve. Now the challenge is to figure out why and how "exhaust"(?) gas gets there. ANY IDEAS APPRECIATED ! I have tried to attach images of the manifold, carb base and power valve. This message was edited by fordmerc on 11-11-10 @ 2:01 PM fordmerc 11-11-2010 @ 2:01 PM reply profile send p.m. New Member Posts: 180 Joined: Oct 2009 another image: this of the power valve / economizer by-pass valve This message was edited by fordmerc on 11-11-10 @ 2:03 PM Stroker 11-11-2010 @ 2:19 PM reply profile send p.m. Senior Posts: 1460 Joined: Oct 2009 I'll go with Supereal's theory that you have a hidden burn-through inside the manifold letting the heat riser exhaust gases enter the intake tract. Stroker 11-11-2010 @ 3:11 PM reply profile send p.m. Senior Posts: 1460 Joined: Oct 2009 Some of us, (especially myself), use this forum as a learning experience. My background does not include vintage Mercurys, and I have never seen an intake manifold with the extra port leading to the power valve. The only Merc. manifold I ever had was the later 49-53 4-bolt style, that was designed for the rear intake Holly. So.....I'm really puzzled as to what was the purpose of that extra port. I can't imagine that it was intended to connect to the heat riser passage in the manifold, so I'm assuming that you have a "burn-through". ford38v8 11-11-2010 @ 8:48 PM reply profile send p.m. Senior Posts: 2883 Joined: Oct 2009 Fordmerc, The hole in the manifold is the heat riser. It runs down to both banks, where it connects to the middle exhaust ports. This crossover port through the intake manifold serves a dual purpose. It equalizes exhaust pressure between banks, as the center cylinders fire alternately, and it serves to preheat the fuel entering the manifold to provide a more complete combustion from the fuel vapor. The heat riser meets a dead end at the cast iron carburetor base, and is not channelled to your economizer valve. Some guys have installed an extra wooden spacer at this point to reduce the heat at the carburetor. Some also have removed the intake manifold to install copper pennies in both ports on the block itself, thereby eliminating the heat riser altogether. With the volatility of modern fuel, the heat riser causes more problems than it ever solved anyway, so the penny modification is not a bad idea to do in any locale that enjoys a mild winter. A side effect, though, may not be welcome to some V8ers: The separation of the two exhaust banks makes for a louder exhaust note, particularly if dual exhaust pipes are installed. Your burnt economizer valve looks to me as though you have had considerable backfiring through the carburetor. As the economizer measures vacuum at the throat, it is vulnerable to any backfire, and does not have the fuel wash to keep it clean from these events as the throat has. Even one backfire can and does easily destroy an economizer valve. A trashed economizer valve does not explain the rough running of your engine, but can explain soot black plugs and poor performance. The rough running caused your backfires and burnt economizer, so once you get your distributor timed correctly, you should be on track to get your engine purring like it should. If your distributor is set up correctly, another explanation may be plug wires that are crossed or shorted to one another, or a carbon track on an inner distributor cap, either of which could fire one or more plugs out of time. Alan fordmerc 11-12-2010 @ 7:39 AM reply profile send p.m. New Member Posts: 180 Joined: Oct 2009 I checked again, but my carburetor seems unlike the one ford38v8 describes. I have a hole in the base which connects to the heat riser hole in the manifold, through the carb base, into the chamber formed by the base and body where the economizer valve is scr*w*d into the base. The economizer valve opens into the float bowl. This carburetor(Ford Model 21-29) is essentially the same as a Model 8BA which came from a 51 Merc. All gaskets (3 spares)have a hole to match the carb base. This engine, including manifold, carburetor, all wiring and distributor are newly rebuilt, and have yet to run properly. The rebuilders are considered competent. The car has never backfired since engine installation. My understanding is now that the heat riser hole should be connected to the exhaust system, and yet there is no flow of exhaust gases through that hole, just temperature equilibration ?? ?? Before I pull the intake manifold and then decide I'm out of my league, can I block off the connection between the manifold and economizer valve without harm? (I don't understand what that valve accomplishes Thanks to all for comments and suggestions This message was edited by fordmerc on 11-12-10 @ 7:43 AM

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