Holley "reverse-idle" model tuning

[80Stang]

Is there any way to tune the Holley 2300 "reverse-idle" model's idle circuit to richer? This model's idle system is "tuned" from factory and actually the idle screws are there just to make it leaner from the factory setting. But what if you'd like it a tad richer...

My 350cfm 7448 had the screws all the way in and it was barely enough for the idle, the A/F meter jumped between decent ratio and lean ratio. This is why I'm currently running with a metering block from a 500cfm 4412 all else being from the 7448...but the "big block" must hurt a little on MPG right now.

 

[xctasy]

The answer is no, unless you get inside the carb.

Pages 37 and 44 of the SA Design 1980 book on Holley Carburetors (Dve Emanuel, ISBN 0-931472-08-3 Part No 08-3).


There is no way of doing it unless you

a) drill the idle feed restriction (only ever the idle feed restriction for fuel side, never, ever the idle air bleed system on Reverse idle carbs). Check out the the existing diameter with an imperial drill, and drill it out bigger in 1 thou increases. If its 30 thou, drill to 31. Then check Idle Co % or air:fuel ratio. The result will be a 7% increase in fuel flow, which will get you going in the right direction to a richer idle. Warning. It will change the wide open throttle air fuel mixture, so only do the drill out very, very sparingly.If the wide open throttle setting was 0% on the Co meter, or 12.5:1, then with the idle feed restriction drilled, it will be like 11:1, and will diliver emulsified fuel earlier in the off idle, accleration and cruise phases of operation. This will then mean you have to rework the pump squirter cam, pump squirter size, or PVCR size of main jet size if you go too big.

If you over cook it, don't worry too much. You'll have to use a piece of fuse wire in each idle feed restriction.

Other oprions are

b) reprofile the reverse idle adjusting needle

c) altering the the limiting cap.


The last two won't work because the pieces are pre-sized by Holley, and I have no info on the changes thaey made.


Explanation:

Stock aftermarket Holley's before about the 1976 and most "Off Road Use Only" carbs had a nice cone shaped idle needle which only worked on one circuit, the idle circuit. It controlled fuel bleed, not air bleed like your 350 7448 did.

Despite being called the Idle screw, the Reverse Idle is actually a two circuit adjustment screw.

With the later carbs, the reverse idle works on two circuits, the curb idle and transfer slot. Both circuits are adjusted when the so-called Idle screw is turned, and they work by limiting air bleed, rather than fuel bleed. The existing throttle body has the old curb idle ciruit undrilled, but instillation of another reverse idle metering block will result in a biased fuel delivery which is very hard to calibrate according to the information I have.

 

[80Stang]

Thanks X,

a lot learned this evening as I have spend some time reading just that book you mentioned as I borrowed it from a friend of mine a while ago. Great book by the way!

I was looking at the pic at page 37 and thought of blocking or at least restricting the Idle air bleeds. Wouldn't that result to richer idle that then could be leaned thru Aux Idle air bleed and the needle setting? If the Idle air bleeds were blocked totally, would the Aux bleeds feed enough air to result in proper mixture? Would the quality of the mixture be decent?

Well, maybe too easy a solution. But not a big deal to just test and find out. Current setup works pretty well but I'm always looking to find ways to make it even better.

(Some extra pieces of info; the 4412 metering block is not a "reverse-idle" model; the screws are currently 1 3/4 rounds out, got 58 jets, 6.5 PV. I'm thinking of switching back to 7448's original metering block if I can get this idle issue solved)

 

[xctasy]

Wow, neat thought! Create a rich conditon, and then adjust it out, brilliant! F(j)ord has a better idea :idea:

Since the 200 is half the size of the engines it was designed for, you may just 'get lucky'. Linc200 and Wsa111 have used wire on the power valve, so it may work on the air blead

It's contray to what the book says, but it sounds smart enough to work.

(I'm pretty sure the reverse idle auguments fuel delivery at other parts of the engine cycle. It could be very far out of the ideal. I'd say have a go with some wire pegged in the air bleeds and check the air fuel ratio somehow. .)

 

[80Stang]

Well, I read more of that book.

On page 45 it says that any richening of the idle mixture can seriously alter the overall fuel economy of a reverse-idle carb.

Got suspicious and careful. That's what I don't want because it sure isn't going to score seriously better MPG...

I kinda like the Holley now so I thought of quitting playing with the reverse-idle monster. So I put an WTB ad on our club's webpages. Maybe somebody has a std idle Holley doing nothing. (side note: one more carb incoming maybe...I have already bought 5 carbs for my GEN2 engine, 3 Autolites and 2 Holleys; three of those have been rebuild with a kit, all of them been tested on the engine)

Then I thought of testing the 500cfm on it - why not! Then I thought of testing a workhorse Autolite 2100 300cfm on it - might as well do this, as I have not tested an Autolite in winter weather before.

Well, all it may cost is some fuel to first try the reverse-idle's main idle bleed restriction (starting with this as it is the fastest to do). Hmmm, I was just about to re-string my guitar so there will be plenty of "restrictor wire".

 

[xctasy]

E-flat isn't usefull chord to base your singing on, but the guitar string sounds great.

 

[80Stang]

The Holley is now singing with an "E"-string .052 gauge. I installed a piece of that around the acc squirter and the ends right into the idle bleed holes. First I swapped the carb's own metering plate in with new correct gaskets, so it is now back to pure 7448 350cfm reverse idle setup. 58 jets and 6.5PV in this setup.

With the screws all the way in the string restricted the air as supposed and I started to screw idle screws out (lean the mix) until the A/F started to bounch to totally lean in the A/F meter. Then I screwed back in a bit. They ended up 1 1/2 turns out.

I delayed this post due to that I wanted to burn one tank of fuel first to see if I ruined my MPG. Did NOT! At least it don't show worse MPG than with a std idle 4412 metering block, probably slightly better now.

Next I thought of trying .042 gauge string to get the screws more in, the idle bleeds need restricted just barely what is needed to get the idle not bouching to lean as it does without the string & the screws all the way in.

 

[80Stang]

Got hold of another Holley 350 but guess what, reverse idle eco-model once again. Where are all the normal 350 Holleys? Huhuu??? Well, I have a 4V Holley incoming so I'll check with that, maybe it has a pretty similar metering plate with 350 2V. Got about 10 carbs in the garage...

The best MPG I got with the Holley was 22, in winter climate with electr. choke but with jets as low as 56. This is no worse than any MPG during last summer.

Well, I decided it was time to winter test an Autolite 2100 1.14 so I swapped one in and ended up with the air cleaner housing not compatible with it (I modded one 1946 1V air cleaner to 2V for the Holley) so I put the summer filter back in; the 14x2" open housing. Hoping for dry weathers as I might face carb icing now without snorkel and warmed intake air...weather here is now changing a lot during days, in the morning -10 to -15*C and close to zero C at noon. Snowstorm close to zero will stall this thing...

(2100 1.14 / 59 jets / 7.5 PV / screws about 4 rounds out, only very very occasional lean spots before PV opens)