Is it still fat after turning the idle mixture screws in all the way ?
If your carb is equipped with air bleeds, one is specific to the idle circuit. Just install a larger bleed (jet).
If no bleeds, are the throttle plates drilled with an .080" or so orifice ?
Did you get the aluminum metering blocks with a vacuum circuit? Then they take a different metering block gasket. There is a machining problem with those blocks, the idle circuit crossover (where the idle circuit gets its' supply, down low at about 5 & 7 o'clock) is machined excessively large. If you use a normal metering block gasket the idle circuit fuel will have direct access to the vacuum port going down thru the baseplate. It is hard to see, lay the gasket on the metering block, at the 5 o'clock idle crossover there is a hole in the gasket for the vacuum circuit, in this hole at 11 o'clock it intersects the idle crossover - you won't really see it unless you have a magnifying light - if you take a pick and poke it into that upper lefthand corner (11 o'clock) it will pass right into the idle crossover. The fuel intended for the idle circuit will run right into the vacuum port and dribble into the engine beneith the baseplate. You can mess with the idle circuit screws all day long and they really won't affect anything. Again, this is true only if you have the aftermarket metering blocks with vacuum, like any demon-type metering block. They have a special gasket, it is obvious because the hole for the power valve is round instead of toumbstone shape. These gaskets do not have the hole for the vacuum circuit as race carbs don't have that vacuum port. If you don't have one of those gaskets i'd use a piece of foil type ducttape (the stuff that looks like aluminum, not the cloth stuff), a very small piece, and cover the idlecircuit crossover. That is all that a regular gasket does anyway, just seal it off - it is just a passage to supply fuel to the idle circuit channell.
Good luck, hope i helped oj
What carb? What metering blocks? What size are the idle air bleeds? What size is the idle feed restrictions in the metering blocks? What was wrong with the original metering blocks? And last, how about some engine and vehicle specs...
It's a 400" sbc, track 1's, roller, 14:1, etc. Made 640hp The carb is a BLP model# 40245-1.420 It has .062 idle air bleeds. It really makes no difference if the idle mixture screws are 1.25 -1.675 out. Car will fire evry time with out touching the pedal. It seems fat too me at idle since it acts like it loads up in gear and drops at least 400 rpm from no load. The oil just seems to have a little more in it than normal from last year. I didn't know how many sizes I should go up on the bleeds to make a noticeable difference. It also has a pv in the front block but it checks ok. I would have to call BLP to find out what restrictors are in the metering blocks.
I'm assuming from the catalog it's a gas 4150, 750 main body with an 850 base plate. First, pull the carb and turn it over to double check the amount the t-slots are exposed. They will have about .020 or look like little squares if correct. Double check your timing, at that HP level I'm assuming it's locked out. A good cleaning may be in order, partially plugged passages don't work well. Make sure the bowl screws are tight, crossleaks from a loose gasket will cause issues. If all looks well, go to the local hardware store, buy some stainless 10-32 set screws, brass is preferred but usually harder to find locally. DON"T USE REGULAR STEEL SET SCREWS. Buy a drill index if you can afford it, otherwise see if the hardware store has .065 to .075 drill bits individually. Go up .002 to .003 at a time, if you make it to .075, don't have a transition stumble and still not lean enough you have other issues. It would be a good idea to pull a bowl and check the idle feed restriction size, I would guess it's somewhere between .025 and .035. BLP is closed tomorrow, would have to call Monday.
Thanks J Mark. BLP is open on Fridays now. They were slow during the winter. You are correct on the carb. I know that the transfer slots as you describe are correct. I'll go ahead and use the spare rebuild kit I have to get this thing cleaned up. I like the set screw idea and will try that out. Also I'll call BLP tomorrow but I'm almost certain they are in the .032 range. I'm also going to go ahead and get my vac. pump rebuilt as well to cover all my bases. And yes to the post above timing is locked out with a crank trig.
Open now on Fridays? I'll have to ask the boys about that. I live about 30 minutes away, know most of the guys there. Ask for Joe on the counter for the specs. Set screws are easy to come by, you can order brass at MCMaster-Carr. Same goes for the idle feed restrictions, find out what size they used and you can try going down a little. Once you find the right combo for your engine you can order the right air bleeds if you want it to look pretty. Your engine will generate a strong signal with a carb that size and may be why it needs a little leaning, have you ever tried a Dominator on it?