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Old 05-26-2015, 09:12 AM
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4.2L Carb Noob

My previous YJ was a 4.0, so I'm a total noob to carbs.
Is there a Carb for Dummies thread anywhere? I don't even know where to begin.
The PO did do a Weber conversion, so at least that's a good thing, but I'm clueless otherwise.

Anything I need to know or keep an eye on? How to tune it, etc...?

Thanks for any help.

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Old 05-26-2015, 12:59 PM
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Maybe I should be more specific...

When starting cold, it takes several minutes before it idles without stalling. Revving.
I'll stall at stop at stop signs for the first several minutes.

Any advice?

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Old 05-26-2015, 01:07 PM   #3
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Maybe I should be more specific... When starting cold, it takes several minutes before it idles without stalling. Revving. I'll stall at stop at stop signs for the first several minutes. Any advice?
Sounds like the choke isn't working properly
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Old 05-26-2015, 03:04 PM   #4
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couple things, but all related to chokes and emissions..

first, you should have a thin/flimsy metal hose running from the exhause header to the air cleaner.

your have an after market air cleaner so that hose is missing... it is to divert warmer air to the carb, for cold starting.

you should also have an electric choke... and or a manual choke... before starting the car, when cold, you press the gas pedal, and the butterfly valve will close, restricting the amount of air so the carb/motor runs rich...


the stock carb had a computer with a stepper motor that would make constant adjustments to the air/fuel mixture.... you dont have that either..

so it is a matter of making an adjustment to the air fuel mix at a certain rpm range and using that as an average for all running ranges...

basically the way it was done since the beginning of internal combustion engines.

carbs are basic, but complicated.

the difference between carb and fuel injection is that the carb does everything inolved with metering air to fuel, where as fuel injection controls the amount of fuel injected depending on the results of a bunch of sensors...

carbs use a 'venturi' affect to 'suck' fuel (from a bowl/reservoir) the air that is sucked into the engine creates a low pressure as it passes by a small tube of fuel.

where as the fuel injection uses a pressure pump and injects that fuel thru a small orafice that atomizes the fuel.

kinda all similar but different.

old school folks like me, dont understand fuel injection, and new school folk like you, cant understand carbueration, (rightfully so). as carbs are / have a lot of moving and fluid parts... where fuel injection has a lot of electronic components.


basically like a drive by wire... you arent pressing on a lever which pumps fuel, you are pressing a button which askes if you can get more fuel.

eheheh


btw, Im confused.. I think I talked myself into a circle, (again)..

Im hoping a guru or two can simplify my simplification...
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Old 05-26-2015, 03:10 PM   #5
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Originally Posted by bergovoy View Post
couple things, but all related to chokes and emissions.. first, you should have a thin/flimsy metal hose running from the exhause header to the air cleaner. your have an after market air cleaner so that hose is missing... it is to divert warmer air to the carb, for cold starting. you should also have an electric choke... and or a manual choke... before starting the car, when cold, you press the gas pedal, and the butterfly valve will close, restricting the amount of air so the carb/motor runs rich... the stock carb had a computer with a stepper motor that would make constant adjustments to the air/fuel mixture.... you dont have that either.. so it is a matter of making an adjustment to the air fuel mix at a certain rpm range and using that as an average for all running ranges... basically the way it was done since the beginning of internal combustion engines. carbs are basic, but complicated. the difference between carb and fuel injection is that the carb does everything inolved with metering air to fuel, where as fuel injection controls the amount of fuel injected depending on the results of a bunch of sensors... carbs use a 'venturi' affect to 'suck' fuel (from a bowl/reservoir) the air that is sucked into the engine creates a low pressure as it passes by a small tube of fuel. where as the fuel injection uses a pressure pump and injects that fuel thru a small orafice that atomizes the fuel. kinda all similar but different. old school folks like me, dont understand fuel injection, and new school folk like you, cant understand carbueration, (rightfully so). as carbs are / have a lot of moving and fluid parts... where fuel injection has a lot of electronic components. basically like a drive by wire... you arent pressing on a lever which pumps fuel, you are pressing a button which askes if you can get more fuel. eheheh btw, Im confused.. I think I talked myself into a circle, (again).. Im hoping a guru or two can simplify my simplification...
He won't need the tube off the manifold to stock air cleaner. It sounds like the choke is malfunctioning. Op will get better Advice in the Cj section
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Old 05-26-2015, 03:48 PM   #6
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In the middle picture you are looking at the electric choke. It is the bit with the wire sticking out. Loosen those 3 screws and rotate it to adjust it. If you take off the air cleaner you can see the air valves open and shut as you turn it. Also you can adjust the air fuel mixture by turning a screw and the idle by adjusting a nut. Im on my phone now and cant see your pics all that well but i will look later. Im going through this myself trying to get everything dialed in right but at least we are both learning.
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Old 05-26-2015, 04:38 PM   #7
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starting a carbed motor is different than FI. you pump the gas pedal twice to the floor to set the choke before starting. try that before you go messing with the settings.

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