I know the Dellorto FZD is the Holly Grail of Carburetors mainly I think due to the accelerator pump, but was the dellorto FRG 28 any good or no better really than the Weber iMB 28, this is with regard to the 126 650 motor.
Technical Dellorto FRG 28
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Technical
Dellorto FRG 28
Both the Dell’Orto FRG 28 and the Weber iMB 28 are 28 mm carburettors that were used on small Fiat engines (including the 126/650), but they have different characteristics — and the Dell’Orto often gets more praise for good reasons.
Dell’Orto FRG 28
Solid, reliable carb from Dell’Orto’s single-choke lineup
Uses progressive venturi and well-timed jets
Smooth throttle response for daily driving
Better atomisation than many contemporaries
It’s generally regarded as better all-round than the Weber iMB 28 because:
Dell’Orto’s fuel metering is often more consistent
Tends to idle smoother and respond better off-idle
Easier to tune finely for the small Fiat engines
That said, it’s not as sophisticated as a Dell’Orto FZD, which is the one with the famous separate accelerator pump (that gives stronger mid-range punch and throttle squirt).
Weber iMB 28
Weber’s budget/standard carburettor of the era
Decent performance, easy to jet
Simple design
BUT:
Less crisp throttle response than an FRG
No accelerator pump to help transient fueling
Tends to be a bit richer/less efficient out of the box.
In practice on a 126 650
FRG 28 > iMB 28 in drivability and response.
Most tuners and restoration enthusiasts prefer the FRG over the old iMB on that engine.
Neither matches the FZD in terms of transient response and “punch,” but the FRG is a solid performer and worth fitting.
So in short:
FRG 28 is generally better than iMB 28, especially for everyday use and smooth throttle transitions.
The FZD with accelerator pump is the real “holy grail” for performance, but if you want a step up from a Weber iMB, the FRG is a good choice.
Dell’Orto FRG 28
Solid, reliable carb from Dell’Orto’s single-choke lineup
Uses progressive venturi and well-timed jets
Smooth throttle response for daily driving
Better atomisation than many contemporaries
It’s generally regarded as better all-round than the Weber iMB 28 because:
Dell’Orto’s fuel metering is often more consistent
Tends to idle smoother and respond better off-idle
Easier to tune finely for the small Fiat engines
That said, it’s not as sophisticated as a Dell’Orto FZD, which is the one with the famous separate accelerator pump (that gives stronger mid-range punch and throttle squirt).
Weber iMB 28
Weber’s budget/standard carburettor of the era
Decent performance, easy to jet
Simple design
BUT:
Less crisp throttle response than an FRG
No accelerator pump to help transient fueling
Tends to be a bit richer/less efficient out of the box.
In practice on a 126 650
FRG 28 > iMB 28 in drivability and response.
Most tuners and restoration enthusiasts prefer the FRG over the old iMB on that engine.
Neither matches the FZD in terms of transient response and “punch,” but the FRG is a solid performer and worth fitting.
So in short:
FRG 28 is generally better than iMB 28, especially for everyday use and smooth throttle transitions.
The FZD with accelerator pump is the real “holy grail” for performance, but if you want a step up from a Weber iMB, the FRG is a good choice.
Thank you for your detailed response.
the hobbler
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If you are thinking about trying to find a "FRG", I have the jetting for this carb (for when fitted to the 500), plus a technical "exploded" drawing. If you want a copy of this info, contact me direct on:--- [email protected]
thefiatfactory
Member
main difference between the Dellorto FRG and a Weber 28IMB is the Dellorto has a removeable choke (venturi) so can be sized to suit, whereas a 28IMB you're stuck with the fixed (cast in) 23mm venturi.
For very little extra money and only a simple adaptor, you can adapt a 30 or 32 FRD type carb. Yes the base bolt pattern has a wider spacing, but that's an easy fix... Weber equivalent would be a 30 or 32IBA (from a 127) or 32 ICEV (from an 1100cc 128/uno etc) and all these also use a regular diaphragm type accelerator pump.
SteveC
For very little extra money and only a simple adaptor, you can adapt a 30 or 32 FRD type carb. Yes the base bolt pattern has a wider spacing, but that's an easy fix... Weber equivalent would be a 30 or 32IBA (from a 127) or 32 ICEV (from an 1100cc 128/uno etc) and all these also use a regular diaphragm type accelerator pump.
SteveC
thefiatfactory
Member
personally I like the Solex PBIC style carb for a single downdraft... you can get a cool manifold / valve cover from Nanni Motori to suit a PBIC carb too.
The solex while it may seem large at a 34 butterfly, the internal design of the solex (it puts the emulsion tube right in the centre of the barrel) is by design restrictive, so needs the larger barrel size. Its advantage is it atomises the fuel very well
I'm using exactly this setup on one of the two 550cc high performance builds I'm doing
The 32 and 34 PBIC carb was an Abarth upgrade for the 595. (was also used on the 850TC Fiat 600 and as an upgrade for the 850's too)
Pretty sure the base pattern of the PBIC and other common webers / dellorto's like the FRD series delloroto's and the IBA and ICEV webers too, so this valve cover / manifold will suit those carbs too. Downside of the PBIC is it's installed height. and FRD or IBA is shorter overall.
SteveC
The solex while it may seem large at a 34 butterfly, the internal design of the solex (it puts the emulsion tube right in the centre of the barrel) is by design restrictive, so needs the larger barrel size. Its advantage is it atomises the fuel very well
I'm using exactly this setup on one of the two 550cc high performance builds I'm doing
The 32 and 34 PBIC carb was an Abarth upgrade for the 595. (was also used on the 850TC Fiat 600 and as an upgrade for the 850's too)
Pretty sure the base pattern of the PBIC and other common webers / dellorto's like the FRD series delloroto's and the IBA and ICEV webers too, so this valve cover / manifold will suit those carbs too. Downside of the PBIC is it's installed height. and FRD or IBA is shorter overall.
SteveC
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thefiatfactory
Member
Or if you want to go for a two barrel, IMO you can't go past the Solex 32PHH (Lancia Fulvia carb), manifolds come with the flanges setup for a rubber isolator spacer (which you really need) to stop the fuel getting frothed up by the engine vibrations
SteveC
SteveC
the hobbler
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The problem with the PBIC is finding one in good condition (and complete!) and then finding the correct jets. Also, finding a 34PBIC with the correct 29mm venturi is very difficult because, so I am led to believe, the normal Venturi size for the "34" carburettor was 27mm---but they made them specially for Abarth with a 29mm venturi. Due to this availability problem, I am trying to see if I can get a Weber 34ICH to work on the "695SS" engine that I am building---This carburettor is also available with a 29mm venturi (the size that I am working with). My reason for trying this carburettor?---It is still available new, is not too expensive, jets are easily available, and it is also a "single,down-draught" carburettor. The version of this carburettor WITHOUT a choke (but otherwise identical) is the ICT, which is used in pairs on the older 1300 and 1600 VW engines---1 carburettor per side of the engine,and 1/2 of 1300 is---650. For anybody trying a PBIC, I have the jetting for the '695'engine---Abarth also fitted the PBIC on the '595SS' (but NOT the '595')
thefiatfactory
Member
You can buy Indian made Solex copies...
and I found a NOS genuine Solex 34PBIC 3 from an 850TC, it comes with the 28mm venturi
you just have to know what to look for!
SteveC
Solex Carburetor 34 PBIC For WILLYS JEEP F Head 134 MCS 1018 1029 | eBay Australia
Find many great new & used options and get the best deals for Solex Carburetor 34 PBIC For WILLYS JEEP F Head 134 MCS 1018 1029 at the best online prices at eBay Australia!
www.ebay.com.au
and I found a NOS genuine Solex 34PBIC 3 from an 850TC, it comes with the 28mm venturi
you just have to know what to look for!
SteveC
the hobbler
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Well done----jammy bugger!You can buy Indian made Solex copies...
Solex Carburetor 34 PBIC For WILLYS JEEP F Head 134 MCS 1018 1029 | eBay Australia
Find many great new & used options and get the best deals for Solex Carburetor 34 PBIC For WILLYS JEEP F Head 134 MCS 1018 1029 at the best online prices at eBay Australia!www.ebay.com.au
and I found a NOS genuine Solex 34PBIC 3 from an 850TC, it comes with the 28mm venturi
View attachment 482180View attachment 482181
you just have to know what to look for!
SteveC
thefiatfactory
Member
For anyone following along, this is how Abarth got around the overall height problem with the 34PBIC, they cast up a special carby top cover that angled the outlet 90 degrees.... these are real hen's teeth.
not mine, pics found on the web just for reference
SteveC
not mine, pics found on the web just for reference
SteveC
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thefiatfactory
Member
If you go down the 32IBA path, the adaptor is available, about 60 euro out of italy. It needs to spin the carb about 45 degrees when compared to an IMB, as the axis of the throttle shaft in relation to the mounting bolts would angle the carb otherwise.
A Weber 32IBA has a 24mm cast in venturi, so a very mild upgrade over a Weber 28IMB with a 23mm venturi, easy to tune and jet, has a diaphragm type pump circuit. Fiat 127's and Autobianchi A112's by the millions had these in the 1970's
SteveC
A Weber 32IBA has a 24mm cast in venturi, so a very mild upgrade over a Weber 28IMB with a 23mm venturi, easy to tune and jet, has a diaphragm type pump circuit. Fiat 127's and Autobianchi A112's by the millions had these in the 1970's
SteveC
Last edited:
thefiatfactory
Member
I was browsing ebay this morning, search phrase "solex fiat 126" and a picture of a carby I have never seen before came up, a Solex 32CBI.
Not a carb we ever saw in Australia, and really not that interesting as a carb upgrade for a 126 / 500... but ... it has a cool looking top, that looks like it will fit atop a 34PBIC... I dont have a 32CBI top gasket to check, but looking at pics it seems like it would fit.
Not facing the "right" way like the 595 version of the 34PBIC, as this would face rearwards, but might be a useful bit of info for anyone going down the PBIC path.
what do you think? here's a pic of a 34PBIC "abarth" style top next to the 32CBI top as best as I could get them from online pictures
SteveC
Not a carb we ever saw in Australia, and really not that interesting as a carb upgrade for a 126 / 500... but ... it has a cool looking top, that looks like it will fit atop a 34PBIC... I dont have a 32CBI top gasket to check, but looking at pics it seems like it would fit.
Not facing the "right" way like the 595 version of the 34PBIC, as this would face rearwards, but might be a useful bit of info for anyone going down the PBIC path.
what do you think? here's a pic of a 34PBIC "abarth" style top next to the 32CBI top as best as I could get them from online pictures
SteveC
the hobbler
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Very interesting---just got to find one!
thefiatfactory
Member
I found one, I just have to get it to Australia.... once I figure out if it will fit 100% for sure, which means I need to buy in a 32CBI top gasket first to compare to the 34PBIC top gaskets I have...
SteveC
