The flat spot can commonly be caused by less than adequate accelerator pump shot too. If you can turn idle set screw both in and out and motor runs rougher either way then you are big enough on the idle jet. Pay particular attention to when you screw it OUT, or CCW direction. The lean out, or CW shows up more obvious than the over-richen, lean out will die but too rich may just get rough and not die. If you get rough going rich with screw then you're right as far as idle jet size. The richness will show up less on later models since they started necking back on the hole to hit idle emission specs.

You can always drill the hole bigger but you can't go back after doing so. I used to pick up extra idle fuel and air jets out of the junkyard just to have tuning parts. Pump shooters too.

If the carb has been set up to where the throttle blades are deep in the transfer slots or holes then your flat spot too, they should be set so that the blade or butterfly just begins to expose hole or slot there. The slots/holes act as miniature accelerator pumps themselves, if already exposed then no more fuel addition possible when the throttle is cracked open, and again the flat spot.

 

Because the main idle feed hole with adjustable needle is up front. The back only needs a small hole to feed the transfer only, no curb idle hole in back. The transfer need a little bit of feed so that it is active when the back barrel first cracks open, the transfer is the accelerator pump there. Like regular Holley 4 bbl., the back gets less idle flow.

It can get wonky sometimes though. When they start searching to lower emissions they do all sorts of crazy things. The fuel flow not set by the jet alone, all systems have an airjet that bleeds air into the fuel to make it lighter and react quicker. If they increase the airjet, they can increase the fuel jet too but it could still flow LESS fuel than before. One of those weird things. On pulling done ANY 5200 I ALWAYS mark all jet positions on a piece of paper for future reference. Some are backwards as compared to others. I'm talking known factory built carbs not torn into by anyone before.

Why you do NOT want to mix up the airjets either.

I remember once pulling apart the 5200 on my Mustang II long ago when car just totally spit its' guts out and stranded me. Pulled a long piece of looked like yarn out of the fuel bowl and wondering 'how on earth that got past the filter?'. Like a 4 inch long piece. Just crazy.

I'll go look in a sec, that would  be great!

On an unrelated side note, this is the first car I've ever had that actually still had the metal id tag on it. Lol.

That one shows original application was a '72 Pinto 2.0L ATX

Primary idle fuel jet 55, secondary 50.

Main fuel jet 132 primary, secondary 135.

Note: the catalog is messed up on the idle jet positions. It calls the key number out for primary but is indicating the secondary position in the carb breakdown picture. Vice versa for the other one. The actual numbers I gave you may be right anyway, if they were input into catalog from a simple list instead of that same mis-translation of the call out pic. They WILL be right for values, just may be mixed up as to the position. Five million numbers in a catalog, sooner or later somebody had to fudge up somewhere..... .......

Thinking the primary slightly bigger to have reserve for the curb idle screw, two fuel circuits on the primary side, only one on the secondary. You also want the one with the adjustment screw slightly bigger so that you can go slightly rich with the screw as an indicator you've gone too far, it helps when setting the screw. Of course there are carbs where that reverses so go figure........ ..

From the 'Holley Carburetor Illustrated Parts and Specs Manual' dated 1975, I bought mine around '78 or so.

Would this get me close? The motor is happy now, but wants more fuel and spark advance.

http://www.ebay.com/itm/WEBER-Redline-32-36-DFV-DFEV-DFAV-Carburetor-Carb-Jetting-Jet-Pack-Kit-NEW-/281155905196?pt=Motors_Car_Truck_Parts_Accessories&hash=item417632a6ac&vxp=mtr

Five minutes of research on the web says I'm wrong. Appears Holley and Weber used same nomenclature for jets. Kit should work but I didn't find the main sizes supplied in it, only three may not help.

Kit a bit high to me, I wouldn't use half of it. Once the air jets are locked in, rare to need to change them. I like separate stuff, of course the shipping can kill you........... .

http://www.racetep.com/weberX.html#jets

Your stuff, your choice as always Daddio........ ...........

That one shows original application was a '72 Pinto 2.0L ATX

Primary idle fuel jet 55, secondary 50.

Main fuel jet 132 primary, secondary 135.

Note: the catalog is messed up on the idle jet positions. It calls the key number out for primary but is indicating the secondary position in the carb breakdown picture. Vice versa for the other one. The actual numbers I gave you may be right anyway, if they were input into catalog from a simple list instead of that same mis-translation of the call out pic. They WILL be right for values, just may be mixed up as to the position. Five million numbers in a catalog, sooner or later somebody had to fudge up somewhere..... .......

Thinking the primary slightly bigger to have reserve for the curb idle screw, two fuel circuits on the primary side, only one on the secondary. You also want the one with the adjustment screw slightly bigger so that you can go slightly rich with the screw as an indicator you've gone too far, it helps when setting the screw. I'd be going with the 55 in primary....... .......

From the 'Holley Carburetor Illustrated Parts and Specs Manual' dated 1975, I bought mine around '78 or so.

Would you happen to have the specs for R-6655?, I can't find anything on it, it was on the car and I'm sure it's not what came on there originally. Thanks..

Excellent information AMC- Really good hard to find stuff!

Should help.......... ...go down just past halfway to 'Holley 5200 jets' section.

http://www.mazdatrucking.com/B2200/5200.html

Thanks, I just found that site last night.. Of course the ignition is crap so I probably should fix that before messing with the carb, LOL..

Definitely do replace your ignition first. That's what led me to my belief that I need slightly more richness. (Which, I had wondered, as Chiltons states that one of the emissions features for 72 is an 'Emissions-rated carb'. Then after my discovery that my random miss was distributor cap related, and general running condition was still yet improved by a fresh set of plugs and wires (both under 7000 miles/12 mos in age) this weekend, it's evidently lacking something.

My list of fresh ignition parts: distributor, points (new), condensor (new), rotor (new), coil, wires (new), plugs (new). All gapped and set according to spec, timing set to 8 degrees, verified no vac leaks, new cam, fresh head rebuild, etc. Also new within 7000 miles: thermostat, coolant system hoses, radiator flushed, battery (new, with fresh connections).

Beyond that, it needs more gas. Thoughts welcomed, but carb and tuning parts on the way, anyway. Cause shiney is good!!!

Man I converted my points to electronic long ago, and a mistake not to. The engine just runs so much longer and smoother the whole way. As soon as I found junkyard parts it was done.

Hot ignition clears up a lot of perceived carb troubles. When you put a suddenly hot firing ignition on you can experience a need for slightly more fuel when the hotter spark burns all you have and asks for more. MANY erratic but perceived as incorrect jetting issues can be solved with electronic ignition.

I can tune Weber IDF's with my eyes closed but my 5200 was a 1st time attempt. I know the fuel jets are the ones in the bowl submerged in gas but are the 2 upper jets for air or are they fuel as well?

Great, so there's no way to put smaller air correctors in to richen it up? That means drilling my fuel jets

The ones on the top are the air bleeds.

Oh OK, so if I install the smaller pair that came with the carb combined with the larger fuel jets I installed from the stock carb it should richen it up. I swapped all 4 assuming they were all fuel related. I forget the sizes but all 4 stock jets were larger than the jets in the NOS carb.