Replacing a carburettor is only one step in achieving the performance you want from your car. Problems with other parts will not go away after a carburettor replacement, and tuning your carburettor won't fix leaking head gaskets, old valves, bad piston rings or cracked vacuum lines.
Although a carburettor is easily understood, it can be extremely difficult to find and fix problems with one. Many different engine-related difficulties seem like a carburettor problem, so checking the rest of your engine system should be done before working on the carburettor itself.
Below is a guide to troubleshooting a carburettor installation.
WHEN INSTALLING A CARBURETTOR, ALWAYS
Change the fuel filter:
Dirt that has been freed-up by moving the fuel line will find it's way into the carburettor and cause flooding.
Flush the fuel line:
This will help the filter start clean and also remove dirt and grit that is in the system.
Check for fuel leaks:
Lines and hoses must be in good condition and properly fastened. Any leaking can give the appearance of a carburettor problem.
OTHER TUNE-UP PROBLEMS USUALLY SHOW UP AFTER INSTALLATION...
So, use this step by step diagnostic check list to rule out other problems. You may wish to go through it entirely, or simply skip to the problem you have experienced.
- Begin with a fully charged battery.
- Check the air filter (cleaner):
Hot air tube; is it missing or disconnected?
Air filter element; Is it clean and not restricting air flow?
Vacuum leaks; All hoses connected & in good condition?
Stuck choke linkages?
Clogged intake manifold crossover passage?
External choke: for free operation?
Choke heat tube: Open & not rusted completely through?
Choke pull off operating?
- Check PCV:
Replace every 20,000km.
Distributor cap: Is it cracked or showing signs of carbon tracking?
Ignition points: Adjust to manufacturer's specifications. Is dwell correct? Check points for pits or burning.
Timing. Set to manufacturer's specifications?
Vacuum advance mechanism: Does it advance and retard?
Mechanical advance mechanism: Is it stuck?
Distributor rotor: Is it in good condition?
- Spark plugs (faulty spark plugs often give symptoms like lean mixture - flat spots)
Are they correct for the application?
Gap properly set to manufacturer's specifications?
- Spark plug:
Visual checks for cracks, hardness or brittleness. (no arcing)
Check for resistance.
Connect a vacuum gauge and check for constant vacuum.
Do a compression test to evaluate valve or ring condition.
Disconnect the vacuum line, if the vehicle smooths out, the EGR valve may be the problem.
Thermal vacuum switch check with a vacuum pump.
Fuel filter blocked?
Check for excessive fuel pressure. This is a common cause of flooding.
Fuel volume correct?
What type of fuel are you using?
Flooding: Disconnect and plug the fuel line, run the vehicle until the fuel bowl empties, flush and reconnect fuel line and the new fuel should flush the needle valve seat.
Flooding: Lightly tap the fuel inlet. It will sometimes free up the debris holding open the needle valve.
Overheating: Installation of a heat shield on some vehicles will cure the problem.
Grid heat: Check that it is working; turning on & off correctly.
Acceleration pump: Full stream of fuel and free of air?
Idle mixture adjustment: Done to manufacturers specifications?
Idle speed adjustment?
Blocked carburettor vent or carbon canister?
Overtightened wing nut on the air cleaner will deform the air horn and cause choke problems.
Vacuum connections correct and in good shape?
- Vacuum Leaks:
Hoses cracked? Disconnected? Replace any loose fittings.
Poor carburettor gasket: Not bolted down evenly.
Vacuum diaphragm leaks?
Manifold leaks? Check with oil or water. If the is a leak it will be sucked in and affect RPM.
Uncapped vacuum pipes? All should be plugged.
Brake booster diaphragm or transnfission modulator leaks?
Too many power accessories?
Drive train condition?
Low tyre pressure increases rolling resistance.
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