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Carburetion
Carburetion, Page 2
Carburetion, Page 3
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Carburetion, Page 6
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Something I just found out while researching this story, is that Edelbrock has three different accelerator pump part numbers for their three different carburetors (625/750/800). Just wipe off the pump that comes in the carburetor that you have and go with it. We will cover those later. We have much better leather pumps and a better ‘negative’ pump shot system to cover but I must research the difference in the three pumps.

The tops/float assemblies should be handled with care. NEVER set the tops down on the floats… ALWAYS set them upside down on the choke towers. Remove the floats and the needles. If the needle is a single piece you have a good needle. If it falls apart, springs and weights come apart, you have an off road needle and it is not to be used. In that case, remove the seat using a PENNY (a red cent) and a pair of pliers so as not to damage the seat, tape the needle and seat assembly together, put it in your tool box and try to find some BAJA fool to sell them to.

You will replace them with either a .093” assembly or a hi-flow .110” assembly. There are even a few .120” so called hi-flow needle and seat assemblies floating around out there folks but let me tell you that in all but the most extreme cases, nothing over the .093” assembly is worthwhile. As a matter of fact, in back to back to back testing in a full race application with 30 pound pumps and a low 10 second/ 1.30-60’ car, I could see NO DIFFERENCE. Still, I do run the .110” N&S myself because on paper it should help keep the bowls full… But one thing is for sure, the bigger the needle and seat diameter, the more problematic the carburetor will be with respect to INTERNAL LEAKS.

You should ALWAYS tap on the top of the carburetor at the hinge of the float area to unstick and re-align the needle in the seat BEFORE turning on the pump and/or starting the engine… AND ALWAYS observe the engine during shut down for smoke or a wisp of smoke coming out of the carburetor, a sure sign of internal leak. On long shut down, have someone hang over fenders and watch inside carburetors while fuel pump switch is thrown. Matter of fact, two persons would be better, one looking in each carburetor.

Remember, RAW FUEL RUNNING DOWN THE MANIFOLD AND INTO THE CYLINDERS IS CURTAINS ON THE RINGS AND WALLS. This is not just a tune up. This is DEATH. Just use the small .093” N&S for street and mild competition and forgetaboutit. DON’T FORGET TO USE A SHINY NEW PENNY AND PLIERS TO INSTALL THE SEAT TO AVOID DAMAGE. Use a new penny for each seat! Don’t be cheap.

Setting up the float level is quite simple if you use the .093” N&S assy. And using the standard guide points, from the gasket surface to the welded seam at the end of the float, with the float at rest and the  top inverted, use a 3/8” drill bit as a guide measurement. You can go as little as 5/16” but little is gained and the risks are greater. This applies to the late model small float like the EDELBROCK.

The early carburetors from CARTER w/ the big rectangular float has a 7/32” spec but maybe 1/4” would be better. That’s the LEVEL. The FLOAT DROP is the distance the float hangs down when the top is held upright in its normal position. Here’s the rub. The bigger the needle and seat, the less float drop the better because that’s what causes the needle to get cocked and stuck and leak like a running toilet. So with .110” and larger, a float drop of 3/4” and the  .093” N&S  can go to 7/8” drop.

Measure the drop in the same place that you measure the level. Adjust both carefully taking care to not exert any pressure on the needle assembly itself. Bend the tab in the back of the float and/or the arm of the float itself. Be careful. You will have to go back and forth as one bend affects the other measurement. When done, set the top down on the choke side and return to the main body.

There is a really neat part that came on all old AFB carbs which are throw away items that clip to the needle and wrap around the float smartly. There are plenty of them here and there and any old racer will have a handful in his tool box. No, they don’t use them anymore, too bad; the clip positively pulls the needle out of the seat as the float lowers with the fuel… good move! Bad move that a penny item is left out of late model carburetors.

Some good news: You NEVER have to replace the SEAT again! It NEVER wears out. Occasionally, you could freshen up the needle if there appears to be wear rings that you can feel with your nail, or anything that a good rub-a-dub-dub on your t-shirt doesn’t clean up, but that is rare. These parts last a long time. Also, the size of the needle and seat assembly is determined by the size of the seat orifice so you can use any needle. A good hardy twist type rub against your T-shirt will make the needle like new in most cases. (Why do you think DVORAK MACHINE T-shirts are black? Order yours today! dvorakmachine.com)

All this can be moot as we’ll see in later chapters where we’ll be covering full competition setups-but for the reliable street, maximum performance plus drivability, stay with this setup. There are new SUPER pieces which have evolved, but you’ll need to call me and tell me why you need them… 352.468.1353



 

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