Race Engine Forum UK

Hi Guy,
I am fitting a 1600 8v sohc engine from a Punto into my Fiat X1/9 and want to fit my twin Weber 40 DCNF carbs. The engine will be (for the moment) completely standard apart from the carbs and CSC sports exhaust. I would be very grateful if you could give me some guidance on jetting for the carbs. The setup at the moment is :-

Choke - 30
Main jets - 145
Idle jets - 55
Emulsion tubes - F22
Air corrector jets - 210
Starter jets - 60 F9
Accel pump jets - 35
Aux venturi - 2.5
Needle valve - 1.75

I think this is lean, even for a 1500 so don't want to run the 1600 without first getting a reasonable base to work from.
On a different note, the carbs I have were bought ready mounted on the manifold and appear to be the 'wrong' way round compared to similar setups I've seen - i.e. with the float bowls facing the rear of the car, away from the engine. When I had the carbs mounted on the car, the revs would surge under heavy braking and I was wondering if this was the cause?
Any help/advice you can give would be gratefully accepted!
thanks,
Ben

For a start, DCNF should be mounted with throttle spindle parallel to crankshaft.



Choke - 30 bit small go 32 or 34mm for more power

Main jets - 145 Too big go 125 or 130

Idle jets - 55 Probably too big for a 1600 and you may find the mixture screws need to be wound almost fully closed, I would use 45

Emulsion tubes - F22 OK

Air corrector jets - 210 Probably OK but if top end (5000 plus) is lean go smaller eg: 200 or 195

Starter jets - 60 F9 - no idea, never use them, prefer 3 or 4 full strokes on the throttle to prime manifold with pump jets

Accel pump jets - 35 probably OK but if hesitant on changeover betw idle and main circuit at around 2500-3500 go to 40


Others OK.

Read also: viewtopic.php?f=13&t=647

Use a Facet Silver Top pump (Fast Road) with NO regulator.

GC