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meanone 09-02-13 12:37AM

Where did you set your idle mixture screws at? Try turning them out some to fatten up the idle a little bit. The off idle lean spot is caused by a lean idle cicuit too. I had my mixture screws at 1 3/4 turn out. If you can't get it right go a little larger on the idle jet. Try a .035" mab. That will delay your main, but you may have to jet back up.

frbformula 09-02-13 01:09PM

The idle screws are 2 turns out. Im going to put in a bigger idle jet and try and get the idle into the low 14's. from there I will see if the lean spot clears up.

Meanone did your carb have annular boosters in it? I know the annular ones come on way earlier than the regular ones so I may have put in a bigger MAB like you suggested to keep the booster from coming in to early.

meanone 09-02-13 01:59PM

Yeah, mine were annular. It was an 9375 non hp.

frbformula 09-20-13 12:04AM

Just an update on the dominator

I got it running great. still needs some fine tuning but I love it. I drove the car 45 miles to work then 50 miles to the race track, made 8 passes and then drove it 45 miles home. No issues at all! The car ended up going the same time 11.60s but with a .020s slower 60ft. I could not get it to hook. Then when i finally got the suspension tuned in the shifter broke. So i never made a good complete pass. the car will defentaly be faster when i get the shifter back in order.

Thank you shaker and meanone for all the help!!

meanone 09-20-13 07:27PM

No problem! Have fun and update us after you get back to the track!

Zedo 09-15-14 07:18PM


Originally Posted by meanone (Post 409923)
O.k. Cruise is mainly controlled by the main jets. Try dropping them down two numbers at a time in the front and back and until you get close to a good afr. If your wot afr gets leaner you can fatten that back up with your power valve channel restrictors and the hab's. My car only pulled about 5.5" of vacuum at idle, and at cruise it would increase to around 15". I bet yours is close to the same. Are your main jets still at 86-94?

I'm reading this thread cuz I want to change a Dominator from 3 circuit to 2 circuit. I'm wondering about this post. If he converted from 3 circuit to 2 circuit, there is no transition circuit anymore, it's been plugged or blocked off. The transition circle i.e. intermediate idle jet and nozzles are what is done away with in the conversion.

Or did you mean the idle transfer slot ?

frbformula 09-18-14 12:16PM



I am by no means a carb expert. I know just enough to make me dangerous but im also not afraid to try and learn new things. Read the following link and search around that forum. There are almost step by step instructions on this conversion. The best advice I can give you is get an A/F gage for tuning.

sprint250 09-19-14 01:19AM

Most Xlnt

Zedo 09-19-14 09:31AM


Originally Posted by frbformula (Post 421733)


I am by no means a carb expert. I know just enough to make me dangerous but im also not afraid to try and learn new things. Read the following link and search around that forum. There are almost step by step instructions on this conversion. The best advice I can give you is get an A/F gage for tuning.

appreciate the reply, have already been on that link. I have the hard parts to experiment with here.
easy enough to do- block the 3rd circuit discharge ????? and air bleeds in the original blocks, and see what happens.
also have 4150 blocks from a standard Holley 3310-1 that bolt right on, and are already 2 circuit with power valve.

I already did the research. there's a tendency to over-complicate this mod. It's simple as dirt. taking a carb with 4 discharge holes, and changing it to 3, by blocking 1 hole. not rocket science.

Bill Jones (carb man) posted on a BB Ford thread specifically in regard to 9375/9377 Dominators 3 circuit carbs, and got to the meat of the subject. I linked his posts in the other thread in this forum.

I think what you meant by transition circuit is the idle transfer slot, that feeds from the idle circuit in any Holley block. that slot is used in both 2 circuit and 3 circuit, and has to stay. the intermediate discharge tube above that, is the one that gets blocked in the conversion.

IMHO, the Motorsports Village threads overcomplicate a very simple issue. the threads I read there, went round and round the subject, but don't get to the meat of understanding how it affects the throttle response in the car. 10 different racers come in with 10 different things they tried, give gauge readings, and it's obvious many are doing the opposite of each other. or they come in with carbs they sent out to have done. well then I'm reading the wrong guy if you get my drift. stating what air bleeds they put in, but not a good overall understanding or presentation of what's actually going on in the carb. I got that impression, then another guy came in and actually posted what I was thinking- that he spent hours reading the threads and got nowhere. (I'm not a member)

an A/F gauge would be nice- but for me, it would be like buying a table saw to cut one board. I was looking for someone who did the conversion themself, blocked the 3rd circuit, and then how did the car drive.

Zedo 09-19-14 10:01AM

here's what I'm talking about with the Motorsports Village threads. one guy on page 2 of the thread already got the transfer slot and intermediate circuit terminology mixed up, same question I asked you here at first.

start into the thread, all they talk about are a/f gauge readings, rather than how the car reacts, e.t. and mph. how the car drives is the best indicator to me. these guys are racing but don't have a complete understanding of the circuits in the carb, and what they do. I'd be more interested in the e.t. and mph, not just the a/f gauge readings.

I'm sitting here with 2 Dominators, 2-4160's, and a 4150 on the table, looking to block holes, or swap blocks, to get one working Dominator from that is 2 circuit. the threads are distant from that simple, basic, hands on carb casting work that needs to be done. I can trial/error R&D it myself, it will be an interesting experiment, to post results in a separate thread.

sounds like the mod worked out for you, the car has good road manners and cleaned up idle, and didn't load up on long trips to the track. I may just bolt on the 4150 blocks and see what happens.


Posts: 11441
Location: Coming At Ya!

Phil don't confuse the "T" slot feed with the "Intermediate" (third) circuit! If you're having problems with an off idle rich condition then it's likely the intermediate and possibly the "T" slot with it. With the throttle blades closed you should just barely be able to see the bottom of the "T" slots from the bottom side.
As far as finding out what condition you have goes, if the plugs are sooted up then it's rich, but then again, most 1050 3 circuit carbs will do that anyway?

frbformula 09-19-14 11:47AM

Zedo I agree that they do over complicate the conversion with all there tuning suggestions that at sometime contradict each other. I used that website exclusively for how to do the conversion. I did a lot of reading on tunes on a bunch of forums and made my best educated guess at my base tune. That got the engine running. Then there was about a month or more of trial and error tuning. The A/F gage made it easier to understand what my changes were doing to the A/F under all driving conditions. If your engine is close to what mine was I would put in the tune that I ended up with and then tune from there. It will at least get the engine running.

Zedo 09-20-14 09:06AM

thanks for info. it's just an itch I thought maybe should be scratched. I have these 1150's laying around gathering dust and thought what if ?? and I'm addicted to learning so... thought maybe I'd get one working right. this is $1000 worth of new carbs that 2 friends bought new from Summit and paid for, that ended up being kicked the curb...the finish on them was still new when I got them.

the 3 circuit carbs were designed for IR manifolds with 2-4 apps, that's been in the Holley books and catalogs for 40+ years, this is a type of intake manifold where reversion and resulting backflow into the carb circuits is a serious factor, and each barrel fed just one runner on the intake. the intermediate idle circuit design, is an antiquated 1920's design that feeds in a lousy way, but is resistant to reversion and won't backflow. that's why Holley put it in there. that's also why they removed the power valve on some of those carbs, the reversion would blow the power valves out like a backfire does in no time.

I finally found a post that verified what I was thinking all along, it's just that Holley, the specialty carb guys, and racers almost never don't delve this far into it. but one guy did and he posted a reply. I wanted to know WHY, and how the circuit works, not just the quick fix "try this jet, this air bleed". as it turns out, the 3rd circuit is the same type of carb that is on a single cylinder Briggs or Tecumseh lawnmower, snowblower, tractor engine, which BTW is also an IR manifold with one carb hole feeding one cylinder, with a lot of reversion. I fix a lot of that stuff over the years, esp. recently with the heavy snows we get in winter, and knew I saw that design somewhere. when I mentioned the "mod" I was planning for the the 3 circuit carbs, it involved d/t and installing a needle adjustment for the 3rd circuit, the same as a Briggs or Tecumseh one lunger carb has, which BTW works quite well. this guy mentioned these circuits are typically controlled by needles. did you ever see a carb from those little engines ? it has 2 needle valves, one for idle, one for main jet. they are killer to tune and get dead nuts on at idle, part throttle, WOT just by turning the screws. it's a lot f-ing easier than changing screw in air bleeds and main jets, pulling the carb apart every time ! taking a carb apart every time to do that is just silly IMHO. this is what I was thinking all along. well there you go, he's thinking the same thing I was. notice not a single A/F gauge reading, jet size number, bleed number. but this guy has a firm understanding of WTF is going on, in a 2 and 3 circuit carb. without this firm knowledge first, it's a crap shoot. here is the post:

Post subject: Re: 3 Circuit Dominators

Post Posted: Fri Dec 30, 2011 2:26 am
Joined: Sat Feb 07, 2009 5:12 pm
Posts: 1253
Location: Adelaide Australia

The 3rd circuit on a Holley is a simple dribble with an air bleed design. As such its called a simple single jet design carburetor. It has a separate feed and its only ability to meter is based upon the simple carburetor principle. The density and viscosity relationship of air and fuel are opposite one another. Air gets higher viscosity (thicker) with temperature increase and liquids get less (thinner). Air is compressible (changes density)and liquids are not. The principle of operation of the 3rd circuit of a Holley was dumped from carburetors in 1926. The simple design cannot compensate for the differences between air (gasses) and liquid. What happens with that 3rd circuit is the mixture ratio gets richer as the CFM increases. People can change the position of the outlet and fiddle with the fuel jet and the air bleed but in the end its still a junk design that has to have a restriction placed in the main booster so that it can correct the boosters contribution in response to the 3rd circuits mistakes. It seems to be a counter intuitive way to do it if you ask me.

However there is a reason for the 3rd circuit and its to do with pulsing air flows or rapidly changing CFM. The booster circuit is slow to respond with accuracy to fast CFM changes. For instance if the CFM changes such that an e-bleed is not going to flow air, then fuel will flow backwards via the e-bleed and fill the air well to a new level. During the time the backflow is occurring the volume of fuel involved in that process is not being delivered to the booster so the engine leans out. This is called the problem of shift recovery by some people. If the CFM increases very quickly the fuel contained in the air well has to flow to the booster before the air can exit the e-bleed and cause an AFR change. That fuel is not metered by the main jet at the time of its discharge.

The 3rd circuit on the other hand doesn't have emulsion so it's not effected by backflow issues. That makes a 3rd circuit carby better on the shift or better on pulsing air flows like some cams with tunnel ram manifolds or on individual runner designs.

If you tune by relying on emulsion you will be subjected to the problems of emulsion. If you tune by sizing of wells etc you don't have to use as much emulsion but you may have to use additional mixture compensating devices like needles etc.

As far as comparing performance aspects of a 2 or 3 circuit carby on a dyno there is no reason why each couldn't equal the other with appropriate attention to detail. But thats only on a dyno. Those same 2 carbys would need to be reconfigured to work equally on the track. Pick whatever you want to do, it doesnt matter. There is no justification for one design over the other its more a case of how to interact with the design and usage of the engine, things like useage range, purpose of use and manifolding and valve action etc.

Zedo 09-20-14 09:30AM

what happens is, everyone buys aftermarket metering blocks that still don't solve the problem, then starts laboriously changing multiple screw-in bleeds and jets, instead of getting to the root of the issue first. if a carb guy told me to do that, I'd bounce the custom metering block off his forehead. it should be dialed in when you get it, if he knows what he's doing. if BG can hit it by info I told him on a phone call, they all should be able to.
just changing 4 regular jets is enough of a PITA. changing jets for every circuit and air bleeds for every circuit, that's changing 6 jets on each side of the carb- then changing emulsion jets as well, another 2 to 4 jets per barrel. that is just crazy. those aftermarket metering blocks leave a lot to be desired as a fix, IMHO, and the guys that sell them are doing a lot of bs-ing.

one Briggs needle could do it all with the turn of a screw.

notice what he says about dyno vs. track tuning. what I posted earlier about being more interested in how the car reacts, not the a/f readings, idle bleed, jet size. parallel thinking and approach. it could have the best a/f number going, if the car drives worse, it doesn't matter. talk to the oldest hot rodders in their 70's they all say, build and tune cars for driving style and habits.

notice the comment on the 3 circuit design needing a restriction in the main nozzle, to compensate for the mistakes made by the intermediate circuit. that's probably why the idle ????? are in the main jet wells on a 3 circuit carb, it restricts the main jet well as the intermediate goes richer with cfm increase

meanone 09-20-14 11:32AM


Originally Posted by Zedo (Post 421573)
I'm reading this thread cuz I want to change a Dominator from 3 circuit to 2 circuit. I'm wondering about this post. If he converted from 3 circuit to 2 circuit, there is no transition circuit anymore, it's been plugged or blocked off. The transition circle i.e. intermediate idle jet and nozzles are what is done away with in the conversion.

Or did you mean the idle transfer slot ?

I did mean the transfer slot .

meanone 09-20-14 12:43PM

Buying billet metering blocks solves a few problems when converting an older Dominator from 3 circuits to 2. First it allows you to take the Dom's metering block with the ifr ????? in the main wells and throw them in the trash. Second, everything including the pvcr's are drilled and tapped already. They are very easy to work on. All you need is a "recipe" to set them up. There are no blocks that are perfect for an application right out of the wrapper. Third reason to buy them is that you need blocks that have the idle mixture screws for your 4 corner idling Dominator. Unless you have a few parts carbs laying around to rob them from you'll have to wait for a swap meet or something. Then when you get them you'll still have to set them up for your application wich will require drilling and tapping anyway. These blocks will come off of smaller carbs meant for smaller engines so you'll need to change the ifr, re-jet, and enlarge the angle passage and main well atleast.
I converted my 9375 to 2 circuit using the 3 circuit blocks that it came with before I bought new blocks. It idled and drove pretty good, but it would not fatten up at wot because those ifr ????? are restricting the main wells. Even drilling and tapping the pvcr's and reducing the size of hsab didn't fix it.
Buying a wideband to read afr's was the best thing that I ever did to tune a carb after learning what does what in the first place of course.

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