Stromberg Compatability - Twin Carb Setup Setup

[Jolls]

Hi Team,

I read on here a while back about someone having trouble tuning a twin carb setup where one was a US version and one was an Australian version. For the life of me I can't find this thread now.

Anyway, I happened upon a twin stromber setup for the FC. It has been well weathered and will be getting a complete overhaul. My first step was to strip them down (waiting on a tool to arrive to pull the mains) and determine what I had. The initial clean and strip threw up the following:

• the throttle bodies of both carbs are BXOV-1
• neither of the air horns or carb bodies are stamped with a code
• both carb bodies are 1 1/32" according to the castings
• one carb body was made in the US and the other is Australian
• both carbs appear to be of the correct era in that they dont have the external vent valve

If I recall from the previous thread that there was an issue getting the carbs to synch correctly and there was speculation that the US/Australian versions were slightly different. Can anyone confirm or deny this? I do have a few FE/FC single carbs that I could grab if need be so it isn't a huge issue. I just don't want to waste my time cleaning up the US body if it is only ever going to be useful as a single carb setup. While I am asking questions may I trouble the wise ones with a couple more that may save me some research: Who makes the best kit for refurbishing the carbs; and if there are recommendations on where to get a range of jet sizes for when it comes to tuning down the track?

Finally a shout out to Harv for his excellent guide on Strombergs. If you haven't dowloaded it do yourself a favour. It is an excellent resource.

Cheers n Beers
Craig

[ardiesse]

Craig,

You might have some luck over at FB/EK with Drew's FB Standard wagon thread.  He did an excellent job of troubleshooting his twin Stromberg setup.  And while on FB/EK, get yourself a pair of venturi restrictors.  FJWALLY is the right person to approach.

Carburettor Service Company used to be my one-stop shop, but they've shut down.  I'm at a loss now for rebuild kits and jets.  Extreme Fuel Systems in Narellan?  I think Clay has a good supplier of parts in SA.

Rob

[Jolls]

Craig,

You might have some luck over at FB/EK with Drew's FB Standard wagon thread.  He did an excellent job of troubleshooting his twin Stromberg setup.  And while on FB/EK, get yourself a pair of venturi restrictors.  FJWALLY is the right person to approach.

Carburettor Service Company used to be my one-stop shop, but they've shut down.  I'm at a loss now for rebuild kits and jets.  Extreme Fuel Systems in Narellan?  I think Clay has a good supplier of parts in SA.

Rob

Thanks Rob, will do. Maybe that is where I read up about the US/Aussie compatability issue - would make sense as to why I couldn't find it here.

Venturi restictors are on my list to get. My plan was to cut down the 350 Holly  ones as Harv mentioned in his guide, but if someone has already done the hard yards I will certaibly take advantage of that.

As an aside I just returned from taking the pieces up to the shed and noticed a faint outline of some markings on the airhorn of one carby so I took to them both with some fine wet and dry, carby cleaner and elbow grease. I can now make out the model numbers. Should have been wearing my glasses when I was cleaning them up earlier on the kitchen table while Mrs J was at work and I may not have missed the detail. (I have an excuse - babysitting sick grand daughter - still don't let Mrs J know I wont hear the end of it!)

The model numbers are: 23-105C and 23-30000

23-30000 was on the Australian Carby which dates it as FC-EJ (late 59 to 63).
23-105C was on the US carby so I expect that it was either an iteration prior to the FX-early FC (23-105D).

The FC ute I am restoring is a late 59 model so if there is a slight difference I should be able to use the original carby off it (if it hasn't been changed) or the spare FB motor to make a matching pair. Still keen to know if there is a discernable difference between the US and Aussie versions.

[Jolls]

Just checked the other carbs up in the shed - the one on the original FC motor is no good to me as it is the Auto version off an EK/EJ (23-3001.1). The one off the FB is a carby from an FX to Early FC (23-105D). Interstingly the body from that carby was cast in the US as well, so a real mixed bag of tricks!

[Rod]

Hi Jolls,
I was the fella posting up about issues in synching twin carby’s and questioning Australian vs USA built carbies. Here is the link - Two Issues - Help (possibly related) (fefcholden.club). I never got a definitive answer or was able to problem solve if there is a difference between the carbies. I suspect there may be, but couldn’t be certain because each carby “sucked” differently. Ie: one was lean and one was rich. I did make sure the “tops” matched the “bottoms”. I could never to get the carbies to sync properly. They would sync at idle but would be out of sync on the throttle. The moment I synced the carbies on the throttle, the performance and fuel economy improved significantly, to be on a par of a single carby for economy.

Another point to note, when I used a unisync (CARBURETTOR BALANCER SYNCHRONISER AIR FLOW METER SU WEBER CD SOLEX BUBBLE 4025 | eBay) at idle one carby would always “rich out” and the motor would stall, while with the other carby, this would not occur. The unisync measures vacuum.

To overcome this I purchased a device similar to this ( CARBURETTOR SYNCHRONISER AIR FLOW METER SU WEBER CD SOLEX SYNCHRONIZER | eBay) which measures air velocity rather than vacuum. I did purchase a silicone tube, with a reducer to attach to the top of the carby which allowed the airflow meter to be used. This isn’t the exact one (APS Straight Reducing Silicone Hose 38-32mm Black Reducer Stepper Joining Pipe | eBay) but it gives you an idea.

Using the airflow meter was a dream to use and made it much easier in my situation to sync the carbies on throttle. I hope this may be of some assistance. Oh, the venturi restrictors are a must as is Harv’s Carburettor Bible. We are for every grateful for the time he has put into these guides.

Mmm. This reminds me I need to do some work on my single carby that I have put on my FE now she is back on the road. She purrs at idle, but misses / struggles when accelerating at speeds of around 50 mph. If I use chock, she flies, which indicates that she is running lean. I have kitted the carby and checked the accelerator pump (leather) and she is squirting fuel into the manifold nicely. I have purchased a new oversized throttle shaft, and I am going to have a crack at reaming the throttle body to match. The worst that can happen is I will stuff up (probably likely) but I will learn. Lucky that I have a number of carbies to go to. I am hoping the manifold gasket is not leaking / sucking.

Sorry for rambling on.

I got my power jets and main jets from the states when I couldn’t purchase them readily in Australia. Try this link for jets - Stromberg Carburettor Main Jet (Pair) 0.046" Suit 97, 81, 48 & 40 Series | eBay
Try this ebay seller as well for kits - HOLDEN SINGLE BARREL STROMBERG CARBURETTOR REBUILD KIT SB-652 | eBay. I have received carby gaskets from them and they have been excellent. They appear to be in Sydney.

Here is another ebay seller that I used for the throttle shaft. They are in Echuca, Victoria and come with good reviews - ALLCARB CARBURETTORS | eBay Stores

All the best. With every question you ask, you are one question wiser.

Have a ripper. Cheers Rod

[Jolls]

All the best. With every question you ask, you are one question wiser.

Have a ripper. Cheers Rod

Hi Rod,

Thanks for the in depth response and and the links back to the thread I was looking for. I just went through it again; your eperience certainly justifies doing a bit more research before diving headlong into trying to get this twin setup to work. Maybe the US/Oz carby setup is why the set I have had been left out in the weather! I thought when I headed up to the shed this afternoon that I would be able to get two matching carbs from the four that I have (I thought I had a fifth but can't find it at the moment).  The two Oz ones won't work together as one is manual and the other automatic (that is of course if the air horns are the correct ones for the bodies). The two US made ones are the same model but from different factories and different engineering changes (23-105C and 23-105D).

Based on your experience I will do some more research on the US models to see what the difference is. If I can't get the info I may give it a crack anyway to see how it goes. I did find over on the FB/EK site a similar thread and it turned out to be a difference in the size of the butterfly in the throttle body; meaning one was binding. I will do some checks to see they are correctly sized while I search for a matching carb on ePay.

Cheers n Beers
Jolls

[Errol62]

I have a few bits, BXV2 throttle body and 1 1/32” body and air horn, plus a whole bunch of gaskets, spacers, pump plungers, valves, jets, levers and clips. I don’t seem to have the carb list number, assuming it is a complete carb. Some of this may be if use. I can take some photos and check the spec number on the throttle body, though I think it is bigger than you want?

As far as the supplier of rebuild kits, I gave the number to Vern recently so he may have contacted the bloke. Chris McGrath, carbiologist, Aberfoyle Park SA from memory.


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[Jolls]

I have a few bits, BXV2 throttle body and 1 1/32” body and air horn, plus a whole bunch of gaskets, spacers, pump plungers, valves, jets, levers and clips. I don’t seem to have the carb list number, assuming it is a complete carb. Some of this may be if use. I can take some photos and check the spec number on the throttle body, though I think it is bigger than you want?

As far as the supplier of rebuild kits, I gave the number to Vern recently so he may have contacted the bloke. Chris McGrath, carbiologist, Aberfoyle Park SA from memory.

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Hi Clay,

Thanks for the offer - difinitely too big for my requirements. Thanks for the heads up re Chris - I also have someone very local (a couple of properties over) that does carb restorations as a profession. His wife and mine work together so I will touch base with him once I get a chance.

Cheers Craig

[ardiesse]

Craig,

You can still use the 23-3001 on a twin setup.  The only difference of any note is the vacuum advance port is drilled to give full advance at idle.  You will, for example, be able to use the 23-3001 in the rear position with the advance port plugged, and the 23-105 in the front position, and connect the vacuum advance pipe to it.

Rob

[Jolls]

Thanks Rob,

Great observation - I hadn't considered that as an option.  I am trying to avoid the potential US/Oz issue that Rod outlined below or the different sized throat butterfy that Drew experienced with EK wagon (FB/EK site). The two options as I see it are: the two Australian made (3000 and 3001.1) carbys or alterntively the two US one (105C and 105D). I haven't been able to dig out any info on the 105C so I have no idea what the engineering change between the C and D is so I will probaly run with the Australin made options.

I was aware of the difference in the way the vacuum works between the auto and manual so all things being equal running the vacuum off the manual version makes a lot of sense. Are you aware of what the .1 engineering change is - that is another change I can't find documented.

I'll start pulling it together, find a couple of rebuild kits, borrow a mate's ultrasonic cleaner, gather up a few jet options and I should be prepared for the tuning exercise down the track. Thanks for pointing me inthe right direction.

Cheers n Beers

[my8thholden]

Hi Errol and Craig ..I haven't contacted the guy you gave me Errol I have his number, I just haven't got to the car yet , had too many other things to do  ..Whilst i am here , I want to look at the distributor and the carby ..I feel I might convert a distributor to electronic , what supplier out there offers the best tried and tested electronic ignition for Bosch Grey engine distributor ?  thx Vern .

[Harv]

There are a lot of variables that can make two relatively-similar carbs flow differently. There is the obvious stuff (throttle body diameter, venturi diameter, throttle plate angle) but also some less subtle things - gasket orientation, coke deposits, throttle blade screw profile, main jet installation depth, degree of spray vs atomisation due to jet size etc. Some of the subtle stuff makes little difference, though sometimes it can.

Are the American cast bodies different? Hard to tell, though a flowbench would reveal the answer (there is a geeky part of me that wants to build a flowbench using David Vizard's guidance, and borrow all those hoarded inlet manifolds people have to see what flows best). As Rod found, there will be a difference in flow at idle that may not be linear to the difference at open throttle. You would need to flow bench at varying throttle openings, and then overlay the resultant curves for each carb to see if two were the same.

Is it critical? Not really. If you are running Top Alcohol then yes, you want every cylinder firing the same. Individual throttle bodies per cylinder to regulate flow, and different jetting per cylinder (all tuned via AFR and temperature) are all possible. On a grey motor with a common inlet plenum and siamesed ports then perhaps flow is not that critical.

If you get stuck for bits, give me a yell. I have a fair collection of Stromberg oddments :)

Cheers,
Harv

[Brett027]

I was thinking the same Harv. All the twin manifolds I have seen have a common plenum and again, as you say, shared inlet ports. Because of this, I am not sure what situation other than idle where a slight difference in flows would end up showing up while daily driving. Two strenuous accelerator pumps would compensate for most acceleration issues I'm guessing. The fact that you have to add the venturi restrictors perhaps indicates the plenum effect too.

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[Harv]

There will be some fore/aft effect from two varying carbs, but the grey motor is far from uniform across the cylinders. A good example is coolant flow - even with one of those fancy head gaskets, there will be a difference in cylinder temps. Similarly, the fuel/air rflow path from the for’ad carb to cylinders 1 and 2 is way different to the flow path from fore and aft carbs to cylinders 3 and 4… so they get fed different.

Should you make the carbs as similar as you can? Yep. Should you lose sleep if they are off a bit? Not if it runs well.

Cheers,
Harv

[Jolls]

Thanks Harv, Brett and Vern,

It would be nice to know the difference (if any) between the US and Oz made versions. As I stripped the carbs that came with the setupc down I noticed that one of the throttle butterfly valves was difficult to get out of the throat. This appeared to be a similar problem to what Drew was experiencing with his wagon over on the on the FB/EK forum. I haven't cleaned them up or measured them yet (plan for the weekend that got overtaken by work). Had I not read about Rob's issue on hear some time back I would have accepted the US/Oz carby mismatch and cracked on. It may have been fine or the reason the setup was sitting out in the weather deteriorating may have bitten me in the bum - who knows.

What I was trying to understand is if there is known difference between the US/Oz versions so that I avoid that if it is a potential issue. My take on the advice received so far is that the evidence is anecdotal. The butterfy size difference I will investigate as I will strip down all four carbys this week and see what I find. My plan is to start with the correct  30000/30001.1 combination. I had originally put this aside as an option because of the vacuum advance differences - but as pointed out by Rob this can be easily worked around. Noting that I haven't worked out the differnce between a 30001 and a 30001.1, so there are still potential engineering differences. I will put the US carbys aside for now as they present too much risk of tail chasing down the track given the engineering change between 105C/105D is unknown.
As you point out without a flow bench it is really about trying to address symptoms after the fact. Then it is a matter of being systematic and changing one element at a time until a desirable combination is achieved.

My key takeaways, from this thread and wider reading here and over on the FB/EK forum (more for someone finding this tread down the track) are:

• get hold of and read Vern's carby guide before you start
• if possible use a matched carby setup to start with
• the 30000/30001 combination (manual v automatic used on late FC, FB, EK, EJ manual v EK, EJ auto) is workable if the distributor is connected to the 30000. For completeness if you were installing an EK,EJ auto the reverse would apply
• strip, clean and measure/compare components prior to rebuilding, to eliminate any obvious issues such as mismatched jets, different sized throats, differences in butterfly valves, and correct any differences
• install venturi restrictors before trying to tune the setup.
• you will need to rejet the carbys or they will run rich as you are doubling the fuel intake which will be too rich at idle/low revs and foul plugs
• avoid the adjustable main jets as they are problematic and tend to leak
• 46, 47 or 48 jets on a standard to mild grey motor is a good starting point. 46 appears to be the go to for a stock grey but having a set of each for tuning would be ideal
• purchase a set of carby tools that allow jets to be changed on the car as there is likely to be a bit of fine tuning after installation
• purchase, borrow or make a tuning setup for multiple carburettor setups to make life easier

Again thanks for all of the input. I am pretty sure I am full bottle and ready to ake this next bit on now.

Cheers n Beers
Jolls

[Errol62]

Minor correction Jolls. Harv is the author of the Stromberg carburettor guide you are referring to , not Vern.

Also the EK carbs are 23-3000 and 23-3001, rather than 30,000.
Cheers,
Clay


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[Jolls]

Thanks Clay,

Not sure where my head was at.

Harv, my sincere apologies for incorrectly attributing your excellent work.

[ardiesse]

Craig,

You wrote, "you will need to rejet the carbys or they will run rich as you are doubling the fuel intake which will be too rich at idle/low revs and foul plugs"

This is a common misconception, but in fact isn't true.  Here goes -

Carburettors are designed to deliver a constant air-fuel mixture over a wide range of intake airflow rates (within reason, and excepting full-throttle enrichment).  In a twin setup, each carburettor has half the airflow compared with the equivalent single setup.  Half the airflow means half the fuel delivery in each carburettor; but because you have two carburettors, you have two times half the fuel delivery, in other words, the same as in a single setup.

Conclusion 1: You don't need to re-jet carburettors in a twin setup.  Two BXOV-1s with 1-1/32" venturis and 0.051" main jets will give the correct air-fuel mixture in a grey motor.

Example: the X2.  X2s use two BXUV-2 carburettors with identical jetting as the 149/161 (1-3/32" venturis and 0.055" main jets).  But why did GM use the smaller carburettors when they could have used two BXV-2s, the same as 179/186 (1-5/32" venturis and 0.059" main jets)?  Imagine you're idling along in heavy traffic, in first gear, in your new performance-model HD and a hole in the traffic opens up, and you want to fill it, fast.  You put the foot down.  At idle speed, there's not enough airflow to pull fuel effectively out of the main discharge system, and your hero model Holden bogs down until the revs have climbed enough to get the main discharge system flowing.  Low-speed driveability is why GM went with the smaller carburettors in the X2s.  So then -

Does this problem exist with twin-Stromberged grey motors?  Most assuredly, yes.  In my over-confident youth I hotted up the ex-family EK (rebore, balance, steel timing gears, 20-60 Bert Jones cam, Yella-Terra head, twins, extractors), and it did not like the wide-open-throttle-at-walking-speed treatment.  Not at all.  But the faster it went, the better it went.  I got the better of a 3.3 VB Commodore at about 80 mph near West Wyalong coming back from Perth one time . . .

Enter the venturi restrictor.  In restricting the venturi, the velocity of air at a given volumetric flow rate is increased.  Mister Bernoulli then says that the vacuum in the venturi throat is increased, giving a greater "signal" for the main discharge system to work on, and this results in better driveability.  Except that there's a strict relationship between the venturi size and the main jet size which must be obeyed.  Thus -

Conclusion 2:  When you fit venturi restrictors to improve the driveability of your twin-Stromberg setup, you need to reduce the main jet size to preserve the design air-fuel mixture. 0.046" to 0.048" main jets are the right size here.

Here endeth the lesson.

Rob

[Jolls]

Rob,

Ahh yes - 100% correct.

In trying to "Keep It Simple Stupid" I oversimplified a complex issue. I was trying to lay out the methodology of tuning by laying out the steps in a logical flow. Install venturi restictors, therefore, over rich fuel mixture with the existing jets.

I trust that anyone reading this down the track will take the time to read your addition to understand correctly why they should take the steps to get good performance. Otherwise the twin/triple setups get thrown to the back of the shed in the too hard basket.

I once owned an XU1 that I purchased with a 350 Holley and triples in the boot because the previous owner could not get them to work (Holley or the Triples). After a bit of research I was able to get the Holley to run - big lag on laucnh but punched hard when it finally got some revs up. Jetted it down, changed the acelerator pump cam and it ran much better. Probably should have played with the air flow to get better response but simply put the triples back on and tuned them. Not a problem with them. Bloody car got stolen from Mt Druitt shops - who would have thought? 

[ardiesse]

An XU-1 at the Mt Druitt shops?  That would be like putting a sign on it saying, "Steal me".