Mystery sidedraughts

[Harv]

Ladies and Gents,

Looking for some help please in identifying the carbs in the photo attached. The photo was posted in a HAMB bellytank thread, and some Googling shows it is also on Pinterest.

SROS-110050-TANKERS-72-HR.JPG.jpg

I have a pair of identical carbs that I purchased in Sydney, which had been used on a historic Holden racer (138ci grey motor, running a Repco aftermarket head). Local carb shops could not identify them, so I did a heap of reverse-engineering to get them to work. They appear to be Stromberg variants, but so far I have no leads on identification. Have tried chasing via the HAMB, and via an article that appeared in Street Rodder, but so far no luck. The photo above is of a bellytank, running a Riley motor. These don't look like Riley carbs, and so far I have not had any luck hunting via the Riley clubs.

Appreciate feedback please on the real identity of the carbs.

The history on these sidedraught carburettors has been lost. The seller understood that the carburettors were used on aftermarket Repco heads (Holden "grey" motors, 1948-1963), one in custom road circuit racer, and one in a dragster. The previous owner had the Repco heads stored in a building which burnt down, leaving only the carburettors which had been stored separately. There are no manufacturers markings, stamps or castings on the carburettors. As we will see below, the carburettors seem to take parts from a number of sources, though the photo above from the bellytank thread would suggest otherwise. I checked with Carburettor Service Company in Sydney, and they were of the view that the carburettors were custom cast. Having said that, the castings are very neat, with no obvious occlusions, flash or voids. The main body casting has a yellow dichromate finish. If these are home-cast, they were a very professional job. I’ve checked a number of other period sidedraught carburettors include the Carter YH and Zenith 11ADX12 (and more mentioned in the text below), though again they are very different from these carburettors. If anyone knows the manufacturer of my carburettors, I’d love to hear from you.

The mounting flange is a 3-bolt single barrel non-equidistant setup. It is similar to the 2-barrel Stromberg 3-bolt EE-model (“Stromberg 97”) flange, but not the same. Some Harleys ran 3-bolt non-equidistant flanges (for example on the Linkert carbs), though these carbs look nothing like any Harley I’ve been able to Google. The steel manifold studs are ¼-20/28 UNC/UNFx15/32”. Two of the three studs on each carb have been cast into the Repco manifolds, though it looks like this was done afterwards (drill an oversize hole, insert the stud, then pour in liquid aluminium) as the studs are not altogether horizontal, and the casting is porous around the studs.

The carburettors have a throttle bore of 1 7/16”, an air horn OD of 2¼” and a venturi diameter of 11/16”. The venturis are changeable, being constructed of an interference fit aluminium sleeve, partially pinned in place by the main discharge jet mitred tip. The throttle plate and shaft are both brass, held together by brass 6-32UNCx¼” raised countersink head screws. The screws are hollow point to allow them to be staked in place. The throttle shafts are fitted with brass collars on one side, and brass idle speed levers on the other. The idle speed levers are held in place with 10-32UNFx9/16” fillister head bolts, relying on the bolts to purchase onto the round throttle shaft. The idle speed levers act on a lug on the throttle body castings, and are adjusted with 10-32UNFx7/16” fillister head bolts, locked in place with a #6-32UNCx9/32” cross-screw.

The carburettors have a single float bowl, with the liquid level controlled by a Stromberg EE-type float and screwed hinge pin. The hinge pin drilling has been made all the way through both sides of the casting. One side of the drilling is threaded (to accept the hinge pin threads) whilst the other side has been blinded off by a lead plug. Whilst the floats are Stromberg, Stromberg however only made one type of sidedraught carburettor (the OH model), and this looks nothing like it (the OH for example had a round-shaped float). The needle and seat orifice, located inside the inlet banjo fittings, is 0.104”. This is considerably larger than a standard Holden grey motor (0.070”), and closer to typical Holley (0.110”). The larger diameter needle and seat orifice would support methanol flow for the 138ci grey motor. The outlet of the banjo fittings is sized to -4AN, whilst the inlets are the funky 7/16¬”-24 thread used in Stromberg carburettor fuel inlet threads.

The float bowl is 1 11/16” deep, and contains an integral-cast metering block. The float bowl lid, fastened by three 10-32UNFx9/16” round-head bolts, has a single hole drilled through the casting to vent the float bowl. The hole is drilled at 0.070” diameter vertically, and then at 0.078” horizontally. The float bowl lid also has two brass inserts, probably made by drilling holes and inserting brass rod. The purpose of the inserts, pictured below, is unknown though the photo from the bellytank thread looks like they are rivets for ID tags.

The integral-cast metering block has four vertical passages. The first passage is an air-bleed inlet. Air passes through a brass mesh screen pressed into the side of the carburettor. The air flows through the brass mesh screen and upwards to fill the cavity between the metering block and float bowl lid. Note that the float bowl lid forms two separate compartments – a cavity above the float bowl, and a separate cavity above the metering block. From the metering block cavity, air is able to flow down each of the other three vertical passages.

The second passage is the main fuel discharge. An anti-siphon bleed is pressed into the top of the passage. The bottom of the passage is press-fitted with a mitred steel main discharge jet, which protrudes from the bottom of the metering block into the carburettor throat.

The third passage is the main metering passage. The passage is connected to the fuel bowl by a cross-drilling located some 3/16” above the float bowl floor (shown by the black circle in the image above. The cross-drilling is fitted with a 0.0955” main metering jet. This is a rather large jet, being 3½ times the area of a typical Holden grey motor Stromberg jet. This again points to the carburettors being set up for methanol. The main metering jets are Rochester, which are very similar to Holley. The difference is the threads – Rochester are ¼”-28UNF, whilst Holley are ¼”-32UNEF. Rochester made some sidedraught carburettors (the R and RC models), though these carburettors look nothing like them. The cross drilling is covered by a steel main metering jet plug, which are ½-20UNFx5/16” with an integral washer and 7/16”AF head. The top of the main metering passage is fitted with a screw-in main metering air-bleed. The main metering air-bleed is 3/8-24UNFx3/8”, drilled to 0.039” diameter.

The fourth passage is the idle passage. The bottom of the passage is press-fitted with a 0.093” internal diameter brass seat. The top of the passage is fitted with a screw-in idle air-bleed restriction,. The idle air-bleed restriction is 5/16-24UNFx1.05”. The idle air-bleed restriction is screwed into the idle passage, and bottoms out (seats) on the brass seat. The idle air-bleed (which controls the air flow) is drilled to 0.028” diameter. The idle emulsion-bleed is drilled to 0.033”. Whilst in theory this drilling should control the fuel flow, there is also a restriction where the air/fuel emulsion flows from the idle passage into the main carburettor throat. The carburettor throat has only been drilled to 0.038” diameter. Thus the combination of the 0.033” emulsion-bleed and 0.038” carburettor throat drilling will control fuel flow.

In addition, the four passages have been cross-drilled twice. The first cross-drilling at 11/32” below the top of the float bowl/metering block, connects the air-bleed inlet, main fuel discharge and main metering passages. However, the air-bleed inlet passage cross-drilling is blocked off with a brass sleeve. The second cross-drilling at 27/32” below the top of the float bowl/metering block, connects the main metering and idle passages. The first cross-drillings is sealed at the metering block edge with a drive plug, whilst the lower cross-drilling is sealed with a lead plug.

When the engine is at idle, the throttle plates are near closed. A strong vacuum is formed downstream of the throttle plates, and air flows into the engine. At the idle position the throttle plates are located such that the idle passage drilling is exposed to engine vacuum. The vacuum causes fuel to be drawn from the float bowl, through the main metering jet and up the main metering passage. The fuel flows through the cross drilling, and up the idle passage before passing through the idle emulsion-bleed. The tip of the idle air-bleed tube is submerged in fuel, and air is drawn in through the air-bleed, forming an emulsion in the idle passage. The idle air bleed also acts as a vent to prevent siphoning of fuel from the idle system at high speeds or when the engine is shut off. The emulsified fuel flows through the brass seat, and out into the carburettor throat. Because the idle emulsion-bleed (and idle carburettor throat drilling) is much smaller than the main metering jet, the fuel flow is controlled (metered) by the idle fuel restriction (and idle carburettor throat drilling). To change the idle quality, the idle emulsion-bleed can be made larger (making more fuel flow) or the idle air-bleed can be made larger (causing more air to flow, leaning out and emulsifying the fuel). Note however that if increasing the idle emulsion-bleed much larger, the idle carburettor throat drilling will soon become the restriction controlling idle fuel flow, and will also need to be increased in size.

As the throttle is opened further, the vacuum behind the throttle plates increases. Fuel continues to be drawn into the idle circuit, but is also pulled higher up the main metering circuit. The fuel thus flows from the fuel bowl, through the main metering jet, up the main metering passage, through the cross-drilling and down the main discharge passage. The tip of the main metering air-bleed tube is submerged in fuel, and air is drawn in through the air-bleed, forming an emulsion in the main discharge passage. The emulsified fuel flows through the mitred main discharge jet and out into the carburettor throat. The fuel flowing out the main discharge jet is controlled (metered) by the main discharge jet. To change the engine fuel quality, the main discharge jet can be made larger (making more fuel flow) or the main discharge air-bleed can be made larger (causing more air to flow, leaning out and emulsifying the fuel).

Of note, the carburettor has no transition, power or accelerator circuits. If the carburettor is snapped wide open from idle, a lot of air flows through the throttle plates. The engine leans out, and will either pause or lean backfire. Equally, as the carburettor is moved slowly from idle to wide open the carburettor will initially run on the idle circuit. The fuel mixture will lean out as the throttle plate is opened, up until the point that the main metering circuit begins to flow. At this point, the mixture will rapidly become richer. This performance will give a noticeable effect on engine speed/power when accelerating. With no power circuit there is a risk of insufficient fuel (and either loss of performance or pinging) under load. This would be controlled by running a main metering jet of sufficient richness to cover the worst case load. Realistically, the carburettor has been designed to be in only two states – idle, and flat-out. This makes it useful for drag racing and speedway use, though less useful for street or circuit racing.

The float level is set similarly to an EE Stromberg, by bending the brass tab on the end of the float. Care needs to be taken in setting float level as the cross-drilling between the idle discharge and main metering passages is quite low in the float bowl (exactly the middle). This means that if the fuel level rises above the 50% mark, the float bowl will overflow through the idle circuit.

I’ve gone through and stripped down, cleaned and rebuilt the carburettors. The next step will be to make up some aluminium adaptors to adapt the 3-bolt flanges back to the SU 4-bolt pattern. I’ll then give the sidedraughts a test run on the twin-SU manifold on my test mule Holden grey motor (on an engine cradle). As it appears that the sidedraughts are set up for methanol, and will overfuel on petrol there is a pretty fair chance I set the driveway on fire again

Cheers,
Harv

[GBS]

Have you tried contacting the vintage speedcar associations around the country? Holden engines with all kinds of different carbs were very common in speedway midgets in the 1950s and '60s.

There is also the National Motor Racing Museum at Bathurst and the National Motor Museum at Birdwood just out of Adelaide.

[Harv]

Thanks GBS - will do.

Cheers,
Harv

[T1916]

Hi Harv

Back in the late 80,s I rebuilt the body on a guys midget that was his original car he raced in the late 40,s early 50,s. He,s name was Alan Russack, but raced under the name Alan Marshall (he,s fathers name was Marshall Russack). He raced with he,s mate at the time (Jack Bratham). The car ran a Willy,s jeep motor (with 2 copper head gaskets) running on he,s own mixture of ethanol and peroxide. I remember it had unusually twin carbies, I might be wrong, but I thought he told me they were off an Amilcar?. Alan has since day pasted away, but the car is still out the, number 27. He joined the vintage speed car club and one of the guys told me on the club run around a track on the south coast. They just drive around the track, but they said they could hear him coming and he was sideways around the outside of the track passing them all like he was still in race mode. ( I can,t post pics, but pm me your email and I can send you a pic of the car if you like)


Cheers GT

[Harv]

PM sent - thanks GT.

Cheers,
Harv

[T1916]

Pic sent

Cheers Harv.

[Harv]

For some years now I have been trying to identify the mystery sidedraught carbs that I bought in Sydney, described in the posts above. I’ve tried local experienced carb shops and various old Holden forums, but no luck. The search even led to a post on the HAMB (https://www.jalopyjournal.com/forum/thr ... t-12408685), but was not successful.

During my research, I stumbled across a thread about bellytankers (https://www.jalopyjournal.com/forum/thr ... e.1052568/), that had a beautiful red bellytanker, as seen in the post above. Whilst ogling the #253 bellytank, the carbs caught my eye – those are the same as my mystery sidedraughts! The article on the HAMB forum had been posted in the February 18, 2016 issue of STREET RODDER in the US. I did some digging, and managed to get connected through to one of the car clubs mentioned. Looks like the #253 bellytank was run by Baldwin and Sommerfield (B&S Garage, Hollywood, CA) with the Riley engine and mystery sidedraughts. Baldwin and Sommerfield were SCTA Season Champs in 1956 and 1958. The bellytank is now owned by Jim Lattin in the US, and the club is helping me contact him.

I was feeling pretty happy… then things got funky.

One of the contacts from the car club is a Ford 4-banger enthusiast. He recognised my carbs from an article written in the US F.A.S.T magazine Winfield articles. This lead to a discussion with the gentleman who wrote the aticle. Looks like my carbs are 1933/34 Winfield sidedraughts, from the second production run. Ed Winfield was one of the US’s master go-fast guys of the 1930s (https://www.mshf.com/hall-of-fame/induc ... field.html). His design, production and tuning of speed equipment, especially for early Fords is incredible. The Winfield rocker arm special one barrel carburetors were cast from patterns that were made by Gurz in Los Angeles at the same time the head patterns were built. They were used in 1930’s and 1940’s Indy cars, including the Lencki 1939 Indy car, which is now in the Speedway Speedway Motors Museum of American Speed in Lincoln, Nebraska. The Lencki engine has recently been reproduced by Coker (https://www.cokertire.com/blog/lencki-six-engine). According to the gentleman’s research, there are only about 18 of these carbs surviving.

So all up I’ve ended up with some pretty cool carbs, period correct for a 1930/40’s racer. Just how some hi-zoot US carbs ended up on a Repco grey motor head in Australia is a bit of a mystery… maybe through an Offy speedway engine at some stage.

Cheers,
Harv

[GBS]

[quote Harv] "So all up I’ve ended up with some pretty cool carbs, period correct for a 1930/40’s racer. Just how some hi-zoot US carbs ended up on a Repco grey motor head in Australia is a bit of a mystery… maybe through an Offy speedway engine at some stage.[/quote]

It may have even been this one. Third photo down. https://aussieroadracing.homestead.com/Baker1.html There were plenty of Offys around then and a lot of speed equipment coming in from the US as well.

I think from memory Mt. Panorama started in 1938 while the road was still unsealed. That makes it eighty years old this year. It would be nice to see a few vintage racers, including a speedway midget, driven around on race day morning

I am pleased you have finally identified your carbs.