I am new here and need some help from you motorcraft 2150 experts (I know you're out there ). I have two 2150 carbs #D7TE-AYA and am tuning one for my bone stock 351m on a 78 f150. I got them both used off ebay and am good at re-building them, I got the second one for spare parts. The first carb is on the pickup and running fine. When I got the second carb I took the top off and noticed it has a different booster in it, otherwise the carb is identical to the first one as it should be. Now I'm assuming someone swapped out the booster in one of these carbs. The booster in the parts carb has smaller air bleed holes (the holes the metering rods operate in) and has "A 3Y" stamped on the bottom. The booster in the other carb (the one on the pickup) has "L M2" stamped on the bottom of it, and this booster has larger air bleeds. I have studied these carbs until I almost went blind and am good at tuning them, and the engine runs very good actually with either one, albeit "different". I can go into more detail about that if you need, but what I am wondering is if there is any way (other than buying a Motorcraft Parts Master Catalog for $$$) I can discern which booster# is supposed to go with this carb# as calibrated from the factory - It may make the tuning more "correct". Thanks for any help!

 

These carburetors don't have metering rods for the fuel directly like say a Carter. They were used in the high speed air bleeds on some models to control the high speed mixture. I think that the idea was that it would keep the carburetor from getting too rich as the RPM increased. Usually more air bleed makes it richer down low and leaner up higher but I don't know how this carburetor calibration was set up to work.

All of these carburetors use an annular style booster but there are some differences. A booster cluster from a 4010 Holley can be made to fit. They are still an annular but they are smaller and produce less airflow restriction. As far as I know there was never a down leg stepped style booster made that would fit a Motorcraft carburetor.

 

Thanks for the reply. You are correct these are annular style boosters, which make a nice fine mist. The metering rods, only offered in the 2150 (not the 2100), restrict the air flow according to throttle position - as you open the throttle a cam on the throttle shaft lifts the yoke/metering rods up into the air bleeds restricting them, increasingly so the more you open the throttle (the rods are tapered), richening the air fuel mix as you go. At idle/low rpm the rods are down so you are leaner. This was supposed to allow for a leaner idle/low rpm (to meet emissions) and yet supply an adequate air/fuel mix for sufficient power at higher rpms. Of course the power valve contributes under load (vacuum). There were many different boosters made matched with particular carburetors calibrated for specific vehicle applications, which leads to my question about why my two identical carbs (D7TE-AYA) have different boosters in them. Maybe it was intentional? Or somebody swapped one. The metering rods are adjustable (although Ford says "not to"), and by adjusting one I can get it to run as good as the other, although "different". That's where I'm hung up, without an afr gauge or a Motorcraft Master Parts Catalog I have no idea where I am, just going by the seat of my pants Oh well I've got the one running great now (with the smaller air bleeds) and now I'm looking for what I think must be a small vacuum leak somewhere - I think I'll bush the throttle shaft next and go from there...

 

Annular boosters can be a mixed blessing. I've seen them run very well and also very poorly. Maybe one of your carburetors has been through a line builder/remanufacturer who just tore down a bunch of core carburetors, threw all of the parts in together, cleaned them and then reassembled the carburetors with the parts as the grabbed them out of the basket.

 

Ha Ha that's entirely possible. I suppose I am just splitting hairs, as it runs GREAT with this booster as is and I had to tweak the other one to get it to work, but that one runs great also as adjusted. Going strictly by the seat of my pants the booster with the larger air bleeds just sounds a little "angry", or leaner if you will, and the other booster with the smaller air bleeds sounds just a little "happier", maybe smoother, so I think I'll stick with that one. Vacuum is virtually identical between the two. Throttle response throughout the entire rpm range is awesome. Don't know about mpg yet, haven't gauged that - maybe therein lies the difference? Anyway, can you tell I've had too much time to tinker on this truck? BTW thanks for the info on the 4010 Holley - didn't know you could make their booster clusters work on a Motorcraft carb.