Convert to replaceable idle air bleeds?

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They’re easy to convert for 4 corner. Last one I did was on my mechanical six pack carbs.

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I don't think I have that level of drilling/machining skill...

I'm thinking of just buying a billet primary metering block and tuning the idle, cruise and moderate acceleration... then get a secondary block later (Proform catalog says their block will bolt on to a 2-corner body, although the idle screws won't work). Your thoughts?
 
68 HEMI GTS said:
That’s some crazy example, not something 99.9% will never experience. And it’s minimal at best. And in all honesty that’s easily adjusted for. It’s not the stereotypical thought of the PVCR feeding the engine at idle.
Click to expand...

I never did say it was the common misconception of PV can't be below idle vacuum... you asked for a way it could happen and I referred you to the link. "Never say never" :poke:
 
DrCharles said:
I don't think I have that level of drilling/machining skill...

I'm thinking of just buying a billet primary metering block and tuning the idle, cruise and moderate acceleration... then get a secondary block later (Proform catalog says their block will bolt on to a 2-corner body, although the idle screws won't work). Your thoughts?
Click to expand...

you could, there’s a few different was to go. A QFT plate would probably accomplish the same thing on the secondary’s. Depending how radical the engine is will determine how much adjustability it needs.

nevermind, just seen it’s a pumper. Yes you could add a secondary block with idle screws. Like you said, they just won’t work. It’s worth the effort to mod what you have, if you screw em up then spend the money on new blocks.
 
Would that even fit? I have a 4150 with a secondary block already... it just doesn't have idle screws.

Edited: I too can make typos... it's a 4150 not a 4160 ;)
 
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DrCharles said:
I don't think I have that level of drilling/machining skill...

I'm thinking of just buying a billet primary metering block and tuning the idle, cruise and moderate acceleration... then get a secondary block later (Proform catalog says their block will bolt on to a 2-corner body, although the idle screws won't work). Your thoughts?
Click to expand...


If you are going to do that, you might as well buy two blocks and buy a billet base plate while your at it. Get it tuned up and save your money and when you feel the time is right, you can buy a ProForm main body.
 
DrCharles said:
I don't think I have that level of drilling/machining skill...

I'm thinking of just buying a billet primary metering block and tuning the idle, cruise and moderate acceleration... then get a secondary block later (Proform catalog says their block will bolt on to a 2-corner body, although the idle screws won't work). Your thoughts?
Click to expand...
I see nothing wrong with drilling and tapping your blocks unless you want to save them in original form because whatever.

If you want to go four corner, have someone like 68 Hemi convert the throttle plate.
If you want to buy shiny new aluminum throttle plate, find out which ones come with reasonably sized transfer slots. IIRC Jmarkaudio posted that QF are pretty good that way - but don't rely on my memory about that. Some guys have shortened them with a set screw. I think the guy going by Aquartlow on RFS posted pictures when he did that.

The idle ports are the tricky one. That requires a lot more skill and a good setup. removing the throttle plates I suppose makes it a little easier, but I can't call that easy for the hobbiest.
 
Mattax said:
I see nothing wrong with drilling and tapping your blocks unless you want to save them in original form because whatever.
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As I posted in the ignition timing (+ carb) thread, I decided to go for it. Main body and secondary block are now converted to 4-corner idle :)

If you want to buy shiny new aluminum throttle plate, find out which ones come with reasonably sized transfer slots. IIRC Jmarkaudio posted that QF are pretty good that way
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Yep, got a shiny new Quick Fuel 12-700 and also plugged the dribble holes at the bottom of the transfer slot bore.

Now that it's all together, I'm thinking I should take it all apart again and do the replaceable air bleeds, at least for the idle circuits. I never noticed how much smaller the secondary IABs are than the primary until it was pointed out on tapatalk/racing fuel forum.

Any idea what size to make them (assuming all four the same)? If they should be .070 like the primary ones, I could just pull off the secondary bowl & block and drill the pressed-in ones to size ;)
 
I'd see what GNTKLR, JMarkaudio or Deep roots suggests.
The main relationship is IFR to IAB.
But the secondary side t-slot is mostly acting as an airbleed at idle, so it seems most likely the secondary side may be similar but not the same as primary side.
 
Deep Roots also says to make them the same. Taking it apart again today (actually not a big deal when you have the blue nonstick gaskets, just a few screws).

I may have to have the secondaries opened quite far to maintain my high rpm/low vacuum idle (remember with the 2-corner I was just starting into the secondary t-slot AND had four 3/32" holes in the butterflies). I've drilled a 1/4" hole straight through from the carb stud, and now plan to make a hollow adapter for the top side where the bypass air can get in.

Will see how it goes :)
 
Well then that's prob a good starting point.
Or maybe better start a little smaller. IAb isn't as sensitive as the IFR. And that way its more likely to stay richer as the secondaries crack open.
Are you going to make the secondary IFR's the same as the primaries?
 
Good question. I don't know what size they are (these blocks have the restriction in the well under an expansion plug). If I need to mess with those, first step is to buy some new plugs from allcarbs ;)
 
DrCharles said:
Do I have enough metal here View attachment 1715470593 to drill and tap the primary idle air bleeds?
(Not sure what the thread size is on the replaceable jets, but I could use a brass set screw and make my own).
Click to expand...

My advice is don't bother unless you just like to tinker and you need something to keep you busy. If you want a fully adjustable carb just buy a new one. The new ones have a lot of improvements plus they weigh a lot less. If you really like to tinker then ditch the carb and put a Holley Sniper on there. Then you can play around with air fuel ratio adjustments until the cows come home. The Sniper comes with built in data logging so you can verify what happened rather than just guessing.
 
Its so easy to work on a carb. And with an older one you don't have to deal with fixing the wacky stuff.
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AndyF said:
If you want a fully adjustable carb just buy a new one. The new ones have a lot of improvements plus they weigh a lot less.
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So... you're buying, then? :p
.
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Yeah, I didn't think so :rolleyes: My $60 swapmeet carb plus a few hours of tinkering time is not only a lot cheaper but more educational than plunking down $600+ and then having to tune it also.

Carb weight is unimportant for this project - it's not a class racer. I need to lose a lot more weight than the 8(?) lbs a fancy new carb would save, anyway.

As I've mentioned before, EFI is also expensive and not old-school "correct" which is what I'm aiming for from the start.
 
Today I drilled and tapped all four IABs for 8-32, then installed .070"-drilled screws.
While I was in there, I also did the PVCR's which were huge (.070") especially for #70 (.073) main jets, and those jets give the proper cruise AFR. As a trial I did .052". May still be too much enrichment but at least now I can adjust them ;)
 
I found the article that helped me solve a fluctuating A/F ratio at idle. This level of modification was as deep into carb tuning as I have ever gone. My A/F ratio at idle no longer fluctuates back and forth through the ideal A/F ratio range. It stays within the range.

Relocating the Holley Idle Jet

I never could have dialed my carbs in as well as they are without having a wideband mounted permanently in mounted in my car. For me, it's become a necessary tuning tool. Data Logging would be a luxury, but I haven't hooked it up to my laptop due to not having hooked up the Innovate gauge or downloaded any software to use/log the signal/data.

IFR jets.jpg
 
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I think I may also need to relocate my IFRs (currently in the well near the top)... time to buy some replacement expansion plugs! It does dance around some, but this cam is quite lumpy anyway. Not sure if it will help that much?

(Crossposted from racingfuelsystems Holley board)
A frustrating afternoon under the hood... got brass screws for the choke plate, put the carb back on the engine, turned on the fuel pump and gas started pouring out of the secondary boosters and even the bowl vent.
Shut it back off, cleaned up all the gas, took the rear bowl off... nothing much to be seen, maybe a tiny amount of crud. Anyway I cleaned everything up carefully, put it back together and set the fuel level on both ends with the engine off (just dribbling out of the level holes, 5 psi).

Fired it up, wouldn't idle, waaay rich on the AFR gauge (11.5-12:1 at low speed, 10.5 at 3000). Discovered my original primary idle screws were much more than one turn out from bottomed (the new cork washers were interfering). Fixed that, opened the secondaries slightly, then it would idle at an indicated 14:1 although that figure is not really useful with a big cam with lots of overlap.

It still likes to idle at about 1200 and 8" vacuum with all four screws about 3/4 to 7/8 turn out, drops 50-100 rpm when the fans kick on. Pretty much what it did on the 2-corner idle! A lot of screw-tweaking later, I couldn't make it any better or get any higher idle vacuum (but opening the four idle screws past one turn definitely made it idle worse even without the fan load, so I know I can get rich enough).

Now the tip-in flat spot is back on a short run down the dirt road. I had barely touched the primary idle speed, and don't think I'm more than square on the t-slots, but will try trading off primary for secondary idle speed screw turns. Also need to recheck the primary accel pump to make sure it's squirting immediately. (I'd put the pump cam from my old baseplate on).

And of course then the wideband decided to stop working again during the last shutdown (I really need to pull and clean the sensor).
That's quite enough for one day. At least it was 66 and sunny!
 
I can tell you from my experience that some cams won't like a low IFR. Mine hates it. I know that flies in the face of everything the smart people say (and they are infinitely smarter than I am) so if you move them down and it ain't happy, don't be surprised.

Sometimes it is what it is.

Also, to try and remedy this issue, I've purchased an antireversion plate. The problem with that is it's worthless if you don't modify the top of the intake manifold. And I'm not motivated to pull the intake, weld it up, grind it to size, surface it and then put it back on.

I suspect that plate may make it so I can use the lower IFR. I do believe that is the optimal position.
 
Sounds like you have some room to shrink down the IFR’s. That’ll move your idle screws out a bit and reduce fuel to the TSR slot. I tend to start around .072 on the IAB’s and adjust from there. Usually the big cams need to be somewhere in the 13 range to get any idle quality. Then the trick is keep the cruise from going rich. Personally I’ve had good luck with the lower IFR. The carbs I’ve moved all worked better. Doesn’t mean it’ll work for everything. That’s just my experience.
 
yellow rose said:
I can tell you from my experience that some cams won't like a low IFR. Mine hates it. I know that flies in the face of everything the smart people say (and they are infinitely smarter than I am) so if you move them down and it ain't happy, don't be surprised.
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OK, so maybe I won't move the IFR ;) What cam are you running again?

First thing is to fix the wideband. Probably carbon on the sensor tip. Without the gauge, tuning is unnecessarily difficult!

The return of the dreaded flat spot may be related to t-slot exposure on both primary and secondary. My new baseplate does not have holes in the butterflies... but since I drilled my main body for bypass air, I only have to add holes to the adapter in the air cleaner stud opening.
 
68 HEMI GTS said:
Sounds like you have some room to shrink down the IFR’s. That’ll move your idle screws out a bit and reduce fuel to the TSR slot. I tend to start around .072 on the IAB’s and adjust from there. Usually the big cams need to be somewhere in the 13 range to get any idle quality. Then the trick is keep the cruise from going rich.
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I forgot to mention that I also installed .081 TSRs.
IABs are .070 at the moment. May need to be a bit bigger?

Yes, the actual AFR will likely be 13-13.5 but the wideband may not show that because it's not a true gas analyzer, only measuring O2 in the exhaust...
 
DrCharles said:
I forgot to mention that I also installed .081 TSRs.
IABs are .070 at the moment. May need to be a bit bigger?
Yes, the actual AFR will likely be 13-13.5 but the wideband may not show that because it's not a true gas analyzer, only measuring O2 in the exhaust...
Click to expand...

what kind of meter are you using?
 
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