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Carburetion
Carburetion, Page 2
Carburetion, Page 3
Carburetion, Page 4
Carburetion, Page 5
Carburetion, Page 6
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­By Dan Dvorak
CLOAKING
Also appearing: aandatrans.com and harmsauto.com

CarburetionByDvorak

DvorakCarburetionBannerThis dissertation is the beginning of a long series intended to become a book-Dvorak reveals ALL the secrets he’s learned and applied throughout the years.  Over 20 time NHRA National Record Holder with MAX Wedge machines, this particular offering is geared towards the getting the maximum performance out of the max wedge intake system, HOWEVER, most of the principles and settings apply to the majority of all other multi and single four barrel applications including hot street.

GREETINGS SPORTS FANS AND SCIENCE MAJORS ALIKE… DVORAK HERE….making good on promise number one, the revelation of all I know on calibration, modification and general straightening up of production quality aftermarket CARTER, EDELBROCK and WEBER type carburetors and their specific use on the CHRYSLER MAX WEDGE (or equivalent A&A) CROSS RAM INTAKE MANIFOLD.

Many of the items covered herein will be applicable to most other applications because this is a state of mind after all, and when we can actually SEE some of the problems, you cannot only use some of the things we cover on your big block or small block single and dual carb apps but you can go even farther and come up with your own ‘secrets.’
Remember, these carburetors are made by the tens of thousands and the dies, molds, cutters and things, wear out and/or get sloppy. Some things are designed sloppy so that there is a limited liability; like throttle shafts. The manufacturer sure doesn’t want those things ever hanging up at WOT! (Like the outboard Holley 6-Packs did…). We will show you how to tighten those up too without endangering your tow car.

So, let’s get to it then.
We will start at the beginning… for those who just want to get their ‘ride’ running well, perform respectably, without very much hassle, expense or time consumption. We will also assume NEW late carburetors, Edelbrock/Carter and older Carters with the thin throttle blades and large accelerator pump; 600/625 CFM and 750CFM. They can have any throttle linkage on them since we are going to change that out anyway; most, no doubt, will have the factory original Chevrolet dinosaur linkage. (I have a huge pile of that stuff if you know anyone that wants it.)

Disassemble the carb completely, taking care to not lose the ball or weight under the shooter. Pull the jets and discard. This is a good time to look at all the gaskets under the four boosters and shooters to see that they are not curled up and misaligned, that the holes are aligned properly and they are absolutely flat. These are great carburetors. There is almost never a need for a carb renew kit or gaskets since these parts never go bad. They never become submerged in fuel and they last forever, almost, so most of the time all that is necessary is some spare stuff and some TLC. However, when they sit with old fuel like our sample carb here, especially fuel + ethanol, (napalm, which is just jelly gasoline) all bets are off. They’ll need to go to a carb restorer like Scott Smith at HARMSauto.com


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


THIS IS AS GOOD A PLACE AS ANY TO TELL YOU TO NEVER SOAK THESE CARBURETORS IN CARBURETOR CLEANER/COLD PARTS CLEANER OR HYDRA-SEAL TYPE PRODUCTS. Those products are typically a ‘basket’ type dip aluminum cleaner that will take the meat off your hands and is still available despite our friends at the EPA. It will also take the protective finish off the carburetors and they will corrode and grow things that are unidentifiable!  Use a spray carb cleaner like SUPER TECH 2000 ™ from Wal Mart; it’s cheap, cleans like the dickens, takes paint off and will remove your eye so be careful….but will not harm the finish. If the carb is stained and really nasty, your choices are, leave it stained but clean or have it restored, re-plated or re-finished…  (go to harms.com or see our next installment…)   

For the competition minded, we can get a quicker bowl fill by bypassing the long and restrictive distance of the needle valve and get immediate filling as soon as the needle is even slightly out of the seat orifice. This enables even less float drop as well as lower fuel pressure to the carburetor. It is accomplished by either drilling a small hole into the side of the seat intersecting the well just above the seat itself where the needle seals the fuel off.  (Extreme care and deburring is necessary) OR a flat slot can be machined in the side with an 1/8” end mill which will intersect the body and have a nice approach.

An easy to build fixture must be constructed to do the deed. Before the hole or slot is made, the seat should be installed in the carburetor top snuggly and the position marked where the seat is adjacent to the tin tab that is riveted to the carb top. That’s where you want the fuel to spew out, sort of a splash guard that will cause the least problems.

SHOOTERS/SQUIRTERS

These things have changed as the years have gone by but the short version of the story goes like this… Buy a kit from Edelbrock that contains an .043” squirter and use it, or if you have an Edelbrock carb with a .024 or larger, chuck up a .040” drill bit in the drill press, use some WD40, hold the squirter in your hands and drill the tubes yourself-just be careful to not punch through. That size gives the perfect balance of volume and velocity that splashes against the booster helping atomize the fuel. It helps immensely in eliminating stumble. In this regard, be sure you have .500” pump shot as measured from the tip of the accelerator pump to the top of the cover. Bend, fold and mutilate as necessary to have smooth working linkage after you have installed your max wedge throttle arms.

JETTING AND OTHER SPECIFICATIONS:

No matter who you listen to, whoever you get your tips or ‘hot set-up’ from, what I am about to tell you absolutely works and nothing has been proven to be better on the max wedge manifold. Hot weather, cold weather, altitude, humidity or under water, nothing seems to have much effect on the jetting. Maybe you can eke out a thousandth or two or a shade of color on the plugs only perceptible under an electron microscope, but for all intents and purposes, follow this formula and you will have an extremely accurate metering system that works always, and is ESPECIALLY friendly in the most important area, instant response off idle and drivability.

JETTING IS THE SAME ON BOTH CARBURETORS (although there may be some disagreement-ignore it)
EDELBROCK/CARTER THIN BLADE COMPETITION LATE CARBURETORS
600/625CFM-Primary Jets .098”/.098” (.071”/.047” Rod) / Secondary Jets:  Throttle .089” Choke .082” thin throttle blade angle/Primary 0/Secondary 5
750CFM-Primary Jets .104”/.104” (.071”/.047”Rod)/ Secondary Jets: Throttle .095”
Choke .086”  throttle blade angle-Primary 0/Secondary 5
CARTER OE MAX WEDGE AND OTHER EARLY AFB 500CFM/600 AND 750CFM THICK BLADE
500/600/CFM-Primary Jets .095”/.095” (.071”/.047” Rod)/ Secondary Jets Throttle .086”  Choke .080”  thick throttle blade angle Primary 0/Secondary 12
750CFM-Primary Jets .101”/.101” (.071”/.047” Rod)/Secondary Jets Throttle .089” Choke .077”
thick throttle blade angle-Primary 0/Secondary 5
SOMETHING ON JETS: DON’T GORILLA THE JETS. IT ISN’T NECESSARY. THEY WON’T FALL OUT. MAYBE A DAB OF NEVER SEIZE ON THE THREADS AND JUST A TEENEY SNUG. THEY HAVE A TENDENCY TO WELD THEMSELVES IN THERE. SAVE YOUR CARBURETORS!

NOW all that being said, and having polled several of my racer friends and carburetor builder buddies, there is no clear consensus on the perfect jetting, but we could swap carbs between us and it is unlikely that we would see much if any difference. The answer to this phenomenon lies in the poor design of the factory crossram manifold. (Did I say that?) My approach is to concentrate on smooth and accurate drivability with no lay down, no noises, instant starts and clean acceleration. The rest seems to take care of itself.


A great story to insert here. Once upon a time I decided to really science out the jetting dilemma on the Max Wedge manifold. I had a manifold off the car, carbs bolted on, tops off and fuel in the bowls to a proper level. I then raised the front of the manifold to simulate the lift of the car and altered the jet pattern to observe the fuel spill through the boosters as the level moved away from the jet in one bowl and toward the jet in the other bowl. Long story short, the jetting was bizarre!

Off to the track we went where we performed the typical A-B-A test and guess what? No difference! I was so distraught, I jerked the tops back off and REMOVED the back jets completely and you guessed it….no difference. Don’t do this at home. There could have very well been something else wrong. But the point is, CONCENTRATE ON DRIVEABILITY.

Follow the secondary scheme provided and you will be happy.

Most of the jetting described here is available OTC from Edelbrock (also available from dvorakmachine.com), but for the experimenters, we have blank jets with .020” starter holes and a nice approach. Now I heard the same BS you have about the drilled jet actually running leaner than the factory jet but don’t you believe it! We have done back to back to back tests on carburetors/manifolds where jetting really does matter and drilled jets work every bit as good as factory jets… so there!

Some things you should notice so far: I always use the same metering rods, a .071”/.047” (Edelbrock P/N 7147) because:  a) it comes in all the Edelbrock carburetors so availability is easy;  b) I love the splits of .024” differential between the economy step and the power step;  c) if we ever do change a jet we will maintain the same splits which will keep our all important drivability intact and;  d) when we get to a later chapter on all out competition, we will be discarding the metering rods entirely and running on pure jet only!

While we are in the area of the metering rods, not enough can be said about the smooth and free operation of the piston/rod/spring assembly when you go from high vacuum to Wide Open Throttle, (WOT) in an instant. That is what separates the men from the boys and what separated the smiles from the frowns. First things first, the small spring clip that holds the piston to the rod? Well, we just unhook that and throw it away. If you look closely, you will see that it cocks the piston downward such that it drags the piston against the walls of the carb top as the rod is pulled out of the jet, slowing the rod down and scuffing the piston... Carburetors that have been run always have to be polished in the piston bores and the pistons. They work fine without the spring clips. Get inside the wells and polish the heck out of the walls and pistons, turn the pistons upside down on the rods and run them up and down with light oil and check for burrs.  

Step up rod springs. Rarely in our world have we ever used any other springs than red (orange) or pink. Sometimes they need to be modified a bit to get you to perfection and again we are looking for UD, ultimate drivability. Before we make that final adjustment, a bunch of other considerations must be addressed. We should default to orange (red) to begin and install the retaining plate such that it doesn’t cover the top of the piston completely and you can observe the action of the piston while the engine is running, all four pistons should be visible and half the opening is open and the screw is tight.

Things that don’t seem important, but are important. We don’t want to get too far down into the engine but we need to assume that at some level, this manifold/carburetion system is a relatively new combination so we need to be certain of a few things like the alignment and fit of the manifold gaskets; that they fit the ports nicely and the bolts screw into the holes easily, (NEVER REUSE MANIFOLD GASKETS) and that the bolts have washers on them that take up most of the opening of the bolt hole and that no one wallowed out the bolt holes to make the manifold ‘fit.’ That’s important. Vacuum signal will be weak and even lost if this fit is done poorly. Different thickness manifold gaskets are available from us or many other places if you get in trouble.
More gasket match…

All these manifolds, especially original equipment, are porous and suck oil and air out of EVERYWHERE! I sealed one up and pressured it up to 15 pounds and sprayed soap water on it and it looked like soap-bubble-boy out of every pore, under the manifold, on top, the bolts, studs, everyplace. The only fix is to PAINT the underside of the manifold with a quality oil and heat resistant EPOXY paint, many coats, paint brush will do, and the top with an epoxy primer before you color paint it. ALL STUDS, 4 inside carb studs, bell crank stud, and throttle hold down bolts all get silicone.

The gasket should match the manifold. If you have a small hole manifold, don’t use a one hole gasket or a four big hole gasket. Use a gasket with four matching holes to the manifold and of course they will also match the carburetor! NEVER REUSE THE CARBURETOR GASKET! They leave imprints of the circuits in the base and they will never install exactly the same as they did the first time. Go ahead! Grab an old carb gasket. Look at it closely; it will look like 3-D. You will lose signal and idle quality. When you find the right gaskets, buy a handful. Keep them fresh! Call me!

DRIVABILITY: we’re back to that again. What we are looking for is to first have the carburetors synchronized, that is, having each passing equal quantities of air through the air horn at idle. This is the only slightly complicated portion of the tuning.


BUT FIRST YOU WILL HAVE TO INSTALL YOUR MAX WEDGE THROTTLE ARMS if that’s your intention to do so. If your carburetors are late Edelbrock, 625/750, they will have Chevy arms, no choice, and they are ugly and the ratio is terrible. If you are lucky enough to have some older Carter 9636 or many other numbers made for Chrysler, the arms will work just fine, or you can remove the arms from any of the older carburetors and transplant them right onto a new shiny Edelbrock, or you can buy brand new reproduction models from myself or A&A (AANDATRANS.COM) or others through Chrysler Power for that great look. SOME MODIFICATION REQUIRED. Feel free to call me. Not a big deal. Works like a champ.

I’ll move on assuming we can all handle this. Once this is done and the accelerator pump arm is installed and adjusted to .500” tip to cover, and the throttle snaps open and closed quickly and accurately, close the blades to zero.

NOW WE NEED TO CHECK AND ADJUST THE THROTTLE BLADE ANGLES:  First, and now that the blades are closed, be reasonably certain that they fit the bores well. If this is an all out racer, we need to make this adjustment absolutely perfect. (Another chapter will be necessary.) If it’s very good or close enough, which it should be, go on to the next step which is:  make up a gauge out of an index card using a protractor marking 0 degrees 5 degrees and 10 degrees on both sides of 0 (see picture) and lay across base holding throttle wide open and observing what the angle of opening is. All carbs that I know of have a 0 degree primary blade specification and that adjustment is just under the idle speed screw. Usually, some grinding is necessary to the new throttle arm you have just installed, but be frugal. DON’T GO PAST ZERO. If you do, you will have to get the welder out. The secondaries are much easier as there is a tab that contacts the body that limits the opening and can easily be bent with pliers.

Since we’re talking about throttle blades, let’s talk about ‘almost’ throttle blades and that would be the weighted air door just over the secondary throttle bores.  For all street driving and most street/strip applications, leave the door alone. For competition only, remove one of the weights and hold on!

MULTIPLE CARBURETOR SYNCHRONIZERS
You can build your own or you can buy one from us. I just don’t know any way around it. There’s just no way to do this job, to put multiple carburetors in sync, without this tool. Anyone who doesn’t want to buy one can borrow a tool from us, just call! With the blades closed, open them to 2 turns. Install the carburetors. New gaskets, carefully tightening the nuts, use washers. Install return springs and spring brackets.

NOW WHAT?  
For the max wedge manifold, install the center stud (don’t forget the silicone), install the bell crank and put a drill bit through the bell crank into the manifold to lock the bell crank in place. Adjust each linkage rod out until it just snaps on the carburetor ball and bell crank ball, but does not influence the carburetor. It should be close. Hook up the fuel lines, turn on the pump, tap the back of the carbs with the handle of a screwdriver while someone observes the inside of the carburetors for internal leaks. Best if another person has control of the pump switch on the ready for some violent signal to kill the switch, at least the first time around! (No smoking please…)
THE REASON I AM SO HUNG UP ON THIS INTERNAL LEAK BUSINESS IS BECAUSE I CAN THINK OF NO MORE DESTRUCTIVE FORCE THAT CAN BE CAUSED BY THE CARBURETOR. YOU SHOULD TAKE THIS VERY SERIOUSLY. IT CAN SAVE YOUR LIFE AND CERTAINLY THE LIFE OF YOUR ENGINE.
Everything well, fire the engine, warm it up and re-tighten the carburetors. Unsnap the linkage arms from the carbs but continue to keep the engine cleaned out. You can clear out one carb at a time. Place the carburetor synchronizer on one carburetor and adjust the idle to some point on the gauge.  Now go from one carb to the other, adjusting the throttle screws until both are exactly the same AND the idle speed is satisfactory. Keep the engine clear and keep the idle speed adjusted. There is a lot of back and forth action but you are in control.  

STEP UP ROD PISTON/SPRING ADJUSTMENT
Now we’re running and this is the final step in the drivability factor. What we are looking for is: with the engine running at idle and in gear, the metering rod piston should be down and NOT jumping or hunting, but the instant vacuum is released (throttle is touched) there is sufficient spring to snatch the piston and rod out of the jet to bring the fuel to flow in the power step. It’s such a fine line. That’s why we move the plate so we are able to actually observe the piston action. The longer it takes to defeat the vacuum the more lethargic the acceleration. This can be accomplished with different tension springs sold by Edelbrock but as I said, rarely will you need any other than the red/orange or pink. Now you may need the pink and have to clip 2 or 3 coils off of it. No problem. However you have to get to where you are going. Just know where you are going. Piston down at idle but not hunting, but instant up when the throttle is cracked!


CHOKES:
Most all the things I know about chokes are all bad with a few exceptions. However, it helps to live in Florida. If you need to have an operational choke, make it a manual variety like the original.  Brackets are readily available and dual pull choke cable reproductions on sale everywhere, but if you don’t need it to be operational, a really clean coat hanger free method we employ is: ONE SMALL DROP of LOCKTITE in each corner of the blade, taking care not to drip into the carburetor… and the choke will not open again.

A story to be told here is that we built a pair of Edelbrock carburetors for an engine builder for an inline Hemi engine that went to a dyno. One had a choke and the secondary carb did not. A few cylinders had raging high temperatures and a long story short; moving the choke plate to the other carb moved the raging temperatures to other cylinders. The problem was solved by using both choke plates and all cylinders had good temperatures. My feeling is that we should leave the choke plates in and that there is no advantage in removing them. I have run the Max Wedge both with and without the choke plate linkage without seeing any difference. BTW, some of these carburetors have VENT tubes that hang out of the air horn that I have seen people put caps over. DON’T do that.

Use the spark plugs as a ‘window into the mind’ of the engine and read them. It is an old wives tale that cold plugs make more power than hot plugs. There is no cold. There is no hot. There is only correct. They should be nice and white but not chalk. The glue around the base of the electrode should not be boiling out and the color should be established with some hard running. Putt-putting around will produce the wrong color entirely. Good old wives tale is to shut down the engine after a hard run and pull the plugs on the return road or get towed back to the pits to check true color.

SO, YOU BE THE DOCTOR! GOOD LUCK TO ALL. I’LL SEE YOU NEXT TIME... COMING UP…removing the throttle blade attaching screws without breaking them off/ tightening the throttle shafts without bushings and without running the risk of binding them up/ seating the blades in the bores/ flattening the warped bases, even NEW bases/ fuel line sizes/ fuel pressure/ fuel filters/ regulators/ pump, regulator, by-pass line locations/ accelerator cable adjustments/maintenance/ fuel and its effect on carburetor metering/fast idle and transfer slot…

ADVANCED AND FULL COMPETITION: Intake side of the head should have a nice flat surface, the manifold should as well, and in the full competition model carburetor section to come, we shall see just how bad the base surface is on even brand new carburetors, and how they will have to be machined flat usually requiring a minimum of .005” to do the dirty deed. Since the throttle shafts will have to be removed at this point we will deal with the loose little buggers at that time, before the cutters work their magic. Obviously, there are a few operations that a skilled machinist (there are a few AMERICAN MACHINE SHOPS left you know) will need to be called on to top this project off.  Stay tuned… CLOAKING

 

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