Yesterday I replaced my old motorcraft 2bbl with brand new Holley 2bbl! It's the 500cfm 2300 series carb, and it's done wonders for my engine! I don't get gas in the oil anymore, (the old motorcraft was constantly blowing power valves) and a myriad of vacuum leaks made it impossible to tune, and some other stuff, like sticky throttle plates.

I put the Holley on and bam! The truck runs smooth, idles as low as I care to set it, and the mixture screws actually adjust the mixture! In other words, it all works!

I have only one complaint about the Holley, I've lost some of my low end torque. I managed to get some of it back by playing with the timing, but any tips for tuning it to get my torque back? If not I'll just get used to it, this carb has made my old 390 run better than ever!

One more thing, should I lube the chokes linkages and the throttle shafts? Anything in particular I should use, or just some motor oil?

Sam

 

You might try richening up the accerator pump. Lighter timing advance springs may also help. Just need to play with it. Good luck.

 

That makes sense, if I put my foot into it my torque comes back, but it takes a lot more throttle than I like to give it. So I just adjust it with the lock-nut on the linkage?

Sam

 

Advance your timing to around 12*BTDC. If you have it set to the factory setting (6*BTC) that's just plain retarded.

 

I spent some time today tuning that carb, as it turns out the accelerator pump was kicking in too early! I backed it off, and re-set the timing and the thing runs like a champ!

I just hope that blowback protection works the way it should, my old 390 has a burnt valve and it backfires every once in a while. I think that was one of the things killing the motorcraft.

Sam

 

The backfire thing with Holley's has been way overblown. I've run em for 30+ years now and have yet to have a powervalve blown out from a backfire. Enjoy it.

 

Good to know, I've had it on the truck for the last few days and it made the old rig run great! That is, untill yesterday, when something finally let go inside the motor. I'm not sure what happened, but I've had an intermittent missfire for quite a while but it turned into a constant one yesterday... The truck smells like it's running raw gas out the tailpipe and it idles so sough it hardly runs...

Sam

 

You lost low end power because you went from a 350 CFM carb to a 500 CFM carb. A bigger carb with the same number of venturis will do that every time. You would have been better off going with a 600 CFM 4 barrel. Even better low end and better top end. A bigger carb always has consequences. Basic carberation info would have told you this.

 

A 500 cfm Holley is sized perfectly for a 390. It's exactly half of a 750 DP 4 bbl.

 

The problem is not the CFM, it is not enough holes. A Holley tech once told me that "a lot of little holes will out perform a couple of big holes every time." It has to do with air velocity thru the venturi and 2 big holes suck at low speed for moving air.

 

Times 2 on that.

 

Half a 750 4 bbl is not "two big holes" for a 390. Been there, tried it too many times. A 500 cfm 2 bbl works perfectly on a 390 (and a 400 too). A 600 4 bbl meantime has a tendency to want to open the secondaries too often, on a 390 due to the higher vacuum generated, unless you install the stiffest secondary spring.

 

I beg to differ. When I went from the stock Ford carb to a 500 the top end improved but low end suffered. When I switched to the Holley 350 CFM the bottom end came back and the top end was pretty much the same as the stock carb. Then switched to a 4 barrel intake and a Holley 600 CFM and everything got better. Big holes hurt the bottom end, it is physics and wishful thinking and hoping will not change that. Oh and butt dynos lie worse than politicians.

 

Same principal as the the 4 valve heads. A pair of 1" intake valves will flow more air than a single 2", but they also have a higher velocity even at low RPM. Velocity makes a HUGE difference, in the grand scheme of things.

 

And this is why Ford dropped the FE big port heads and intakes in 1966 except on the truly Hi-Po engines and went to the small ports heads and intakes with street improved performance.