General Category > Quadrajet Carb Talk and Tips
Hesitation when taking off
Cliff Ruggles:
Swapping parts around isn't the answer without knowing what sizes the sizes of the other items involved.
A Carter unit sporting the same part number may not be set up exactly the same as a Rochester.
Instead of guessing I measure everything, upper IAB's, lower IAB's, DCR's, bypass air, mixture screw hole size, transfer slot length and location, etc before making any changes. With the correct information we can make small changes to improve fuel delivery in the areas where the engine is wanting it.
There are ways other ways we can make educated changes. If you suspect the carb is a tad lean at light part throttle causing the hesitation right off idle you can temporarily tip the choke flap in slightly to richen things up then lock it there for a quick test drive, for example.
My "tip-in" test works well to tell us if the carb is lean at part throttle. Set the fast idle around 2000rpm's then gently "tip-in" the choke flap and see if the engine speeds up? If it speeds up more than about 200 rpms then the jet/rod relationship is pretty lean for what you are doing and going to a .001-.002" smaller primary metering rod will put some fuel in that range.
If the problem is at a very low throttle opening transitioning from idle to the main system we can put more fuel there with a slightly larger idle tube and/or opening up the DCR's slightly.
None of these changes are irreversible, as we can also go back to the stock set-up and even the other direction if/as needed........Cliff
Kavesh:
Thanks Cliff, really appreciate the advice.
I understand that you as a pro builder will make sure that the internals are what they need to be for the client.
In my novice rebuilding limited skill and tools, I am able to do the basic stuff. Understanding exactly how everything works is also not easy.
I do take your advice though and have removed the additional airhorn gasket. I have also read somewhere that raising the float level will richen the mix, which may help my off idle hesitation.
Currently I have my float set at 11mm or 0.43 inches. This level as far as I know is the factory setting.
Is there a direct relationship with float level and rich/lean at idle and off idle.
Cliff Ruggles:
Are you using an OEM float or brass?
That float setting is really low for one of those carburetors.
I'd use the correct OEM nitrophyl float set at 1/4" (.250") and see if that helps some.....
Kavesh:
I am using the OEM float.
I have raised the float level as suggested and removed the clip from the needle and seat as it was giving me some trouble.
It would appear that I am running too lean at idle. When I close the primary flap slightly and cover my palm over the primary side the idle speed picks up and the idle smooths out.
As I do not have smaller primary rods, but have 76 jets, I am going to try that today. I am assuming that the larger jets will at least confirm that I have a lean issue at idle. Yes I also realise that the 76 jets in all likelihood will be too big for my application but its will at least narrow down my problem and then I can look for suitable rods for my 71 jets.
Kenth:
Changing main jets will do nothing for idle leanness.
As we´ve discussed earlier, the idle circuit is a standalone circuit and it supplies engine with A/F mixture at idle speed/low speed.
You will have to look into idle tube restrictions (idle jets), upper idle air bleeds, downchannel restrictions (DCR), lower idle airbleeds, off-idle slots, idle mixture discharge holes (at idle mixture needles) and idle bypass air for suitable sizes for what you are doing.
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