Setting carb mixtures and balance on a Guy Croft Fiat 2 liter TC engine

Using Gunson Colortune on each cylinder to set idle mixtures on a pair of Weber 44IDF carbs on a GC StIII 8V TC Fiat rally unit and a Webcon Synchrometer to balance the carbs - barrel to barrel via air bleed screws shown with screwdriver and carb-carb with the balance quadrant. If you can't get a stable setting on the idle mixture screws it's a sure sign the air bleeds are set wrong. One air bleed screw on each carb must be shut - and that will be on the barrel flowing the most air. The setting of the air bleeds has a major effect on the idle mixture screws - very little air flows past the throttle plate at 750-850 rpm idle speeds and if the air bleed is too much open (screwed out) that cylinder will run lean and - even with big idle jets fitted (this one has 50s) - if you screw the idle mixture screw out so far it's almost falling off you won't get that cylinder to richen up. That's exactly what I had on this engine - 1 & 4 plugs showed hardly any evidence of burn at all until I reset the air bleeds whereas 2 &3 where over-rich at idle. The problem was that the air bleed screws on 1&4 were about 2 turns open (causing leaning) and 2&3 were shut. Closing down 1&4 screws and then checking with the Synchrometer showed that air bleed imbalance was the problem.

Category:

Autos & Vehicles

Tags:

• Guy
• Croft
• Fiat
• Twincam
• engine
• racing

[Eugenskill92]

hi, do you have an electric fuel pump? is it better than the mechanical fuel pump? thanks!

[fzer123]

hello! what are you setting the kg/h at? I have my triple webers at 3.5 and am thinking that is high enough...