j9fd3s

Mr Hanover has been good enough to point out that you can hook a tube into your Weber's float bowl drain plug and then run the engine and not only can you set the float level, but you can see if the pumps can keep up.



construction of this devices seems complicated, but it is in fact amazingly easy. the weber float bowl drain is an 8x1.00 thread, which just so happens to be the same as the brake or clutch bleeder screw on every stock mazda rotary.



if you're cheap you could borrow the one from the clutch slave just for this test.



you then use the same clear tubing you'd use to bleed the brakes. the weber drain plug comes out, the bleeder screw goes in like its made for the job, and it will seal on the weber crush ring.



turn on the fuel pump(s) and look for leaks.



Mazda's spec for float level is 21-23mm down from the top of the throttle body/float chamber.

Lynn E. Hanover

There are a number of ways to do that. By the book from a Weber manual.



With a 25MM tall needle and seat assembly Needle closed of course. 5.5 to 6MM of the float should show above the edge of the float chamber walls.



There is a spring you can buy to stuff in beside the float to hold it up. Or, you can turn the carb cover upside down

and make the measurement.



This is stock installation (probably from a V-12 or V-8 Maserati.



This would work with up to 3 PSI of fuel pressure.



If you are a performance nut job, and have installed this beautiful carb on a Mazda, you probably want a bit more



fuel pressure to keep up with the engine at play.



The quick way to adjust float level is: Dial up the fuel pressure you plan to use. Then:

Bend the tab a bit so the float comes up a bit, and keep doing this until the booster venturis just start dripping. Good for all out drag racing,road racing, auto cross, Track days and Gymkhanas. Not good for mileage of any kind.



For normal street use, all the same but when the booster start dripping, go back one step to stop the dripping. Then shake the car side to side, Boosters should drip a few times and then quit when the shaking stops.



The all out racing fuel pressure is 6 PSI on a 300 or 350 or 400 needle and seat. Plus all of the carb tricks.



Higher float= richer mixture. Lower float=leaner mixture.



Be sure the float never touches the float bowl cover.



The bigger the needle and seat, the lower the float will have to be set in order to develop enough pressure to stop the flow. Same for higher fuel pressure. Find a Gross jet setup if you can Try Mazda Trix and others for these.



In the all out set up the higher fuel pressure keeps the fuel level higher (and thus richer) for high RPM use.



Piece of cake.



I can tell you how to do a floatless carb but there will be some fires, and shops burned down. Works great, but has a steep learning curve.



Lynn E. Hanover

j9fd3s

it turns out making the tool is easy, trying to get an accurate measurement is not...



still neat to play with though!



the raise it up till it drips and then drop it down a tad method is much much easier

sen2two

floatless huh? care to explain further on that?

Lynn E. Hanover

OK, but you must swear that you will never do this.......



In the olden days when only diesel trucks had fuel injection, those old guys road raced cars with stock carbs or Solex or Webers or Holleys. The fuel would splash about and change the mixture every 50 feet or so, and racing was less fun than it could have been.



Carbs have bowl vents in various locations and in various forms. The vent is to let air pressure press on the top of the fuel. And to let the bowl maintain ambient pressure. Bowls must be vented into the engine side of the air filter.



So any spillage or spray is ingested and is not set fire to by the exhaust system. So if you fill a carb up with solvent to a normal level, and then shake it hard side to side (about 1.5 Gs) note that solvent is going everywhere from the bowl vent.



So one might fill a bowl cover to level with the mating surface with epoxy filling in the stock bowl vent. One then installs a brass tube dead center over the bowl center and flush with the epoxy. This gets a plastick line into the air filter. Nearby this vent in the bowel cover another brass tube is installed. Perhaps this is the center tube from a table lamp. (In the olden days they were brass). A nut on the epoxy side and a nut on the upper end and the depth of the tube end could be adjusted. This brass tube is reduced on the upper end and a hose is attached going to a sliding vane fuel pump of good capacity. The pressure out line from this pump goes back to the tank. A fuel supply pump is run through a restrictor then supplies the carb as usual, except the carb has no float and no needle or seat assembly.



Fuel entering the carb raises to the level of the end of the adjustible scavenge tube, and stays at that level, no matter what.



This gives you a constant mixture value nearly as good as fuel injection. The scavenge pump should be run from an unfused switch. A dual wire end from the scavenge pump should run the supply pump through a fused line. So if anything goes wrong the supply pump dies. The supply pump can never run unless the scavenge pump is running.



Never run this setup inside the shop. Lots of gasoline moving fast.



Lynn E. Hanover

j9fd3s

i lol'ed

mazdaspeed7

You never cease to amaze me. Once you take float height/fuel level out of the equation, half of the complexity of carb tuning is no longer an issue. So whats a little fire hazard? Its like the missing link between carbs and fuel injection.







Edit: after re-reading it, you are using the air cleaner housing to collect the extra fuel for the scavenge pump to pick it up and send it back to the tank? Yikes...

Lynn E. Hanover

No, the bowl is vented to the engine side of the air filter to be sure that the jets are seeing the same exact air pressure as the chokes, lest the jetting change with throttle opening.



The scavenge pipe (the center tube from a table lamp) hangs down into the carb to the same fuel level that you would see in the stock carb at idle. At low speed and idle where the scavenge pump is very effectively out running the restricted supply pump, you get a rock solid fuel level and the idle jetting will need to be a bit richer as air flow will be from the engine side of the air filter into the float bowl through the new bowl vent. So a 1/4" vent hose minimum is needed. The air filter never sees any raw fuel unless the car is inverted.



At speed all is the same except the massive amount of air through the chokes is producing high fuel consumption, and there is less fuel for the scavenge pump to deal with.



The less obvious advantage is that the missing float volume allows a like volume of fuel in the bowl. So mixture changes caused by consumption rate vanish.



Just as in the dry sumped engine systems, the fuel cell or tank will be getting back more total volume than is being removed by the supply pump. This because air is being scavenged as well as fuel. So, the vent for the cell must be a bit beyond the normal. The normal being a PCV valve (just a lightly sprung one way valve) then a steel (self contained) fuel filter. The hose from this is clamped to the side of the cell and extends (below) the cell in the event the car gets inverted.



With the float in place as in stock, the pressure in the cell from temp changes can be held back (usually) by the float up to 6 PSI. Not the case with no float. So stand clear of the exhaust pipe on start up. The engine may have a cup of fuel laying in the intake.



It is not for no reason that floatless carbs are outlawed in racing. Putting out grass fires, camper fires, and crew members on fire can make for a long weekend.



Lynn E. Hanover