* Timing: Even with spark, if the timing is significantly off, the engine won't fire properly. The spark needs to occur at the precise moment the piston is in the right position. A timing belt that's jumped a tooth or is severely out of adjustment is a common culprit. Check the timing marks on the crankshaft and camshaft pulleys. This is often a complex fix requiring specialized tools and knowledge.
* Compression: If the engine's compression is low, it won't have the power to ignite the fuel-air mixture effectively. Low compression could be caused by worn piston rings, valve problems (leaking valves), or a blown head gasket. A compression test is necessary to diagnose this.
* Carburetor Issues (despite fuel delivery): While you say you have fuel *to* the carburetor, the carburetor itself might be malfunctioning. This is surprisingly common. Issues include:
* Clogged jets: Small passages in the carburetor can become clogged, restricting fuel flow.
* Incorrect carburetor adjustment: The carburetor needs to be properly adjusted for air-fuel mixture. It's possible it's too lean (not enough fuel) or too rich (too much fuel).
* Diaphragm problems: If the carburetor has a diaphragm (likely), it could be torn or damaged, preventing proper fuel delivery even if fuel is reaching the carburetor.
* Flooding: The carburetor could be flooding the engine with fuel, preventing starting.
* Fuel Quality: While less likely, very old or contaminated fuel can prevent the engine from starting.
* Ignition System Issues (despite spark): Although you say you have spark, the *strength* of the spark might be insufficient. A weak spark can be caused by a failing ignition coil, worn distributor cap and rotor, or bad spark plug wires. A proper spark test should measure spark strength, not just presence.
Troubleshooting Steps:
1. Compression Test: This is the most important first step to eliminate a major mechanical issue.
2. Check Timing: Verify the timing marks are aligned correctly.
3. Inspect the Carburetor: Look for any obvious signs of damage, clogs, or leaks. Consider cleaning or rebuilding the carburetor. If you're not comfortable with this, take it to a mechanic.
4. Ignition System Check: Inspect the spark plugs, wires, distributor cap, and rotor for wear or damage. If possible, test the spark strength.
5. Fuel System Check (beyond just delivery to the carb): Make sure the fuel pump is working correctly and that there are no fuel leaks in the lines.
Important Note: Working on a carburetor can be complex, and incorrect adjustments can damage the engine. If you're not mechanically inclined, it's best to take your Geo Metro to a qualified mechanic for diagnosis and repair. They have the tools and expertise to pinpoint the exact problem much more efficiently.
