HARD START ON COLD ENGINE

• Gas Siphoned From Float Bowl: After turning off a hot engine, look down the carburetor to see if fuel is dripping from the main discharge.Blocked or improperly vented vent tubes or vents in the carburetor can create a vacuum inside the float bowl, leading to siphoning of fuel.
• Fuel Evaporation: Fuel may have evaporated from the carburetor bowl, making it difficult for the engine to start. This could happen after a long sitting period.
• Clogged Jets: The carburetor jets could be clogged with debris or residue, hindering fuel flow to the engine.
• Stale Fuel: If the fuel in the tank is old or degraded, it may not combust effectively, causing starting issues.A vehicle that has been sitting for months may have gas that has turned to varnish. The gas tank will need to be removed and cleaned. Simply adding fresh gas will not work.
• Choke Malfunction: The choke mechanism may not be functioning properly, leading to improper air-fuel mixture for starting.The choke valve should be closed with a cold engine. Fully open with a hot engine. When cold step on the accelerator a bit and see if the automatic choke closes. For a manual choke you need to close the choke.
• Faulty Spark: The spark plugs or ignition system may be faulty, preventing proper ignition of the fuel mixture.
• Air Leaks: Air leaks in the carburetor or intake manifold can disrupt the air-fuel ratio needed for starting.
• Moisture Buildup: Moisture accumulation in the fuel system can interfere with combustion.
• Dirty Air Filter: A clogged air filter can restrict airflow, affecting the combustion process.
• Battery Issues: A weak or dead battery may not provide enough power to turn over the engine.
• Sticky Throttle: The throttle linkage or butterfly valve in the carburetor may be sticking, impeding airflow.
• Accelerator pump: Look down the carburetor and pump the accelerator once. You should a good squirt of gas coming out of the main discharge. If none comes our, or it is weak, you have accelerator pump circuit problems. See about the accelerator pump here.
• Main Discharge: It is also possible the main discharge is leaking. After running, shut the engine off and look down the carburetor. Gas should not be dribbling out the main discharge. If it is, then the gas is being siphoned out of the bowl.
• Electrical: I have made no reference to electrical but that should be looked at also. Bad plugs can cause hard starts.