General Category > Quadrajet Carb Talk and Tips
Hesitation when taking off
Kenth:
Today the fuels contains less energy and yesterdays calibration can not deliver proper amounts of combustible air/fuel mixture, especially from the idle/off-idle circuit.
The accelerating pump supplies extra fuel when throttle blades opens rapidly, as in WOT from standing still, and the same goes for the main fuel/air supply.
For normal take-off, the idle/off-idle/low speed circuit delivers most of the needed air/fuel mixture.
And since the todays fuels are "leaner" than fuel was when our carburetored vehicles were new this circuit needs some help.
Kavesh:
Thanks for the replies Kenth, much appreciated and understand that factory settings may not necessarily work with current fuels today.
I will try and do a bit more research into the idle off idle system before attempting any mods.
Would you be able to confirm whether my jet/rods combo is decent for my newly rebuilt 5.0 V8 Holden 308 stock motor.
My primary jets are 71 and rods are 45B
Kenth:
Primary jets #71 (.070"-.072") and rods 45B is not uncommon to see in units with .050" main airbleeds in air horn and float bowl.
Also,remember that the engine gets most, if not all, of the fuel / air mixture from the idle / low speed circuit at lower speeds and that it is involved in higher speeds, albeit to a lesser extent, at higher speeds, as the main circuit takes over to an increasing degree.
Kavesh:
Thanks again.
Perhaps a silly question, but how on earth would i determine the main air bleed sizes or would they be a specific size based on carb numbers?
I would not have tools or access to tools to measure these air bleeds
Kenth:
If you can´t find a pin gage set, some drill bits might help.
1.1811mm .0465" #56
1.2mm .0472"
1.1906mm .046875"
1.25mm .0492"
1.3mm .0512"
1.3208mm .052" #55
Red lines marks the brass insert lower main air bleeds and yellow lines marks the upper main air bleeds in air horn.
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