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exhaust and fuel jets

 
  #1  
Old 11-07-2005, 10:03 PM
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exhaust and fuel jets

got two questions for ya guys and gals. on a freinds bronco im doin some work on, its a auto with a 302, some serious towing package, 1985. on the driverside manifold, theres some kind of valve on the exhaust, on a cable or hose, looks like it shuts off the exhaust on that side, what is it? on the carb, ita a two barrel motorcraft, where is the fuel adjust ment screw(s)? i cant seem to find it.
 
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Old 11-08-2005, 06:26 PM
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The butterfly valve in the bottom of the driver's manifold should have a spring steel coil attached to the valve shaft. This bi-metal spring unwinds when it warms up and vice-versa. Its a heat-riser valve used on older models to retain exhaust heat near the engine until the engine has reached normal operating temperature. It won't (or at least it shouldn't) completely shut down the exhaust from the left bank of cylinders. It merely holds the exhaust up a bit to increase backpressure and heat levels at the engine on cold starts. If it is STUCK CLOSED, there is the potential to OVER heat and reduce fuel mileage. Stuck open jst means that in extremely cold temps, the engine will take a little longer to get up to normal operating temperature. There SHOULD be a flexible metal tube maybe 1 1/4" diameter coming up from the manifolr to the underside of the air cleaner housing. The heat that builds up while the heat riser valve is mostly closed gets drawn into the intake hence warming the intake and the entire engine just a bit faster. As the manifold heats up, the bi-metal spring should relax (unwind a bit) from the increase in temperature. This opens the valve and the exhaust flows normally. Unless its stuck closed, its not really a vital component and many of them end up rusted wide open or the shaft seizes from the endless temperature changes that the manifold sees. So, unless its stuck closed, its not worth messing with.

By 1985, Ford had done what most other auto makers had done and decided that the factory fuel mixture setting was "good ehough" and they capped over the fuel-air mixture screwheads with part of the casting that makes up the throttle plate. If you can see where the needle tips of the screw protrude into the throttle bores, you should be able to figure out where the screwheads are buried INSIDE the throttle plate casting. Some care must be taken when grinding away the casting to expose the screw heads but it can be done. I know, I know, it sounds ludicrous but automakers wanted to make people come back to their dealers to get their cars fixed not fix 'em themselves.
 
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Old 11-08-2005, 06:54 PM
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so there inside the actual castin of the carb? whos smart idear was that one? is that the only way to adjust the fuel mix?
 
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Old 11-08-2005, 07:26 PM
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Yeah, if you look close you can see the "lumps" for lack of a better term where the screwheads are trapped within the throttleplate casting... gotta love it when the engineers get their hands on things. The idea was that if the engine was running properly and the emission equipment was finctioning as designed, the fuel-air mixture should be able to be set and left alone... forever.

Of course thats like saying all you need to put on a show are the actors and place to perform. Doesnt' take into account changability of the weather, daylight, wind etc.

The same is true for the fuel mixture adjustments. As the engine ages and things begin to settle-in, loosen up, etc. adjustments will need to be made. If you think about it that whole concept has done a complete 180* switch. Now fuel-air ratio control is CONSTANTLY monitored and changed by the on-board computer. Fuel-air mixture screws are the only way I know to adjust the ratio on a carb'd engine.
 

Last edited by greystreak92; 11-08-2005 at 07:29 PM.
 
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