Weber DMS 34 jetting for 124 1800 Sport engine

Road-race engines and ancillaries - general discussion
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Abarthnorway - Remi L
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Joined: June 24th, 2006, 1:39 pm
Location: Oslo, Norway
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Weber DMS 34 jetting for 124 1800 Sport engine

Post by Abarthnorway - Remi L »

Hi All!


I am in need of some advice regarding the jetting of a Weber 34 DMSA carb for my lightly tuned 124 1800 Sport engine.
I have close to no experience of setting up twin chokes, but eager to learn:


Engine specs:

1756cc 9.8:1 comp
Modified head, valves, seats, combustion chamber and manifold for better flow
300` cams with 10 mm true lift - mild profile - 2.5mm lift @ TDC when timed 110/110 (measured)
Std bottom end
Std exhaust manifold
Ignition checked and timed correctly.

The engine feels basically quick and sharp - but as of now (one small test run) very rough and "untidy" - I want a better jetting before I dare to test it thoroughly.

Carb details: Originally fitted Weber DMSA 34 201 (swedish specs) - cleaned and all new gaskets.
Current jetting - definetely not right.....and didn`t expect it to be:

Primary/ Secondary
Choke size 25/27
Emulsion tubes f61/f84
Mains 122/145
Airs 180/175
Idle 50/60
Pump 50
Needle valve 1.75
Float level approx 6mm


I have tried to find original jetting figures for the standard 124 1800 sport, but the figures I have found go in all directions varying from
Primary/ Secondary
Mains: 125 to 145/ 145 to 155
Air: 165 to 180/ 155 to 180


Any suggestions for a good base jetting would be appreciated.


Thank You


Best regards

Remi Lovhoiden
GC_45
Guy Croft
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Re: Weber DMS 34 jetting for 124 1800 Sport engine

Post by Guy Croft »

Sorry but I don't know, I'm not that good on single carb jetting,

G
vandor
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Joined: November 30th, 2006, 3:24 pm
Location: Texas, USA
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Re: Weber DMS 34 jetting for 124 1800 Sport engine

Post by vandor »

Hello,

The 34DMSA1 on the 1974 US-model 124 Spider was jetted as follows:

Venturi 25/27
Mains 140/145
Airs 165/155
Idle 50/60
Emulsion tube F7/F7

This engine had a compression ratio of 8:1 and was rated at 92HP/6200 rpm.

This might give a starting point.
bye,

Csaba
Auto Ricambi, LLC
124 Spider Specialists
GC book #288
Marc
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Location: New Jersey ,USA
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Re: Weber DMS 34 jetting for 124 1800 Sport engine

Post by Marc »

140 is too rich for a stock engine,135 main for the primary barrel is near perfect.Fiat had a well known issue back in the day with richness on these carbs.
Major automotive publications critized the car for low speed bucking problems.Some thought it was the motor mounts being too soft! If you buy a 32/36dfev it comes with a 137 main jet which is even better for a car with some mods.The 34dmsa 1/100 was the largest 2 barrel progressive stock carb fitted for the USA market,but the 32/36 is larger on the chokes,simpler design,better choice.I think you will find that a 55 to 60 idle on the main will work best.
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