1. Restricted (dirty) air filter.
2. PCV valve dirty, plugged up, or restricted.
3. Carburetion:
   1. Idle mixture is set too rich.
   2. Idle speed is set too fast.
   3. Idle speed is set too fast because the idle mixture is set too lean to idle properly.
   4. Choke is not opening all the way, or operation is faulty.
   5. Float level is very high.
   6. Float is too heavy.
   7. Leaking gas through at needle & seat and is slowly flooding. (defective or dirty needle & seat). (Check for small piece of dirt on needle.)

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1. Engine problems such as leaky valves, carbon build-up on valves, broken valve spring.
2. Ignition (electrical) problems:
   1. Bad condenser.
   2. Bad points.
   3. Plugs dirty, shorted, worn out or fouled.
   4. Plug wires bad, mixed up, or crossed.
   5. Distributor cap cracked.
   6. Bad rotor.
   7. Bad coil.
   8. Ignition timing advanced too far.

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High O2, high HC, Low CO. Note: Oxygenated fuels can give readings of O2 up to 4% when there is no vacuum leak: this is OK.

1. Leaking vacuum or air at carb base plate. (this is so common, start your search here.)
2. Vacuum leak.
3. Bad PCV valve.
4. Bad or leaking Brake-Booster Diaphram.
5. Dirt in idle jet.
6. Carb base warped by installer.

7. Carb top badly warped by installer.
8. Base gasket missing or wrong one or installed incorrectly.
9. Altitude compensator malfunction.
10. Mixture set too lean.

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1. Idle speed set too fast.
2. No ground circuit to the idle cut-off solenoid.
3. No power up to the idle cut-off solenoid.
4. Defective, dirty, or non-working idle cut-off solenoid.
5. Carb is slowly flooding. (Needle & seat dirty.)
6. Power valve blown out by engine spit-back.
7. Fuel pressure too high.
8. TPS (throttle position sensor) not adjusted correctly.
9. Dirt in air bleed jets.
10. Bad O2 sensor.

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Or with possible solution #3 it may run OK or just be a little low on power.

1. Engine problems such as leaky valves, carbon build-up on valves, broken valve spring.
2. Ignition (electrical) problems:
   1. Bad condenser.
   2. Bad points.
   3. Plugs dirty, shorted, worn out or fouled.
   4. Plug wires bad, mixed up, or crossed.
   5. Distributor cap cracked.
   6. Bad rotor.
   7. Bad coil.
3. Bad Catalytic Converter

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1. Vacuum leak
2. Float level too low.
3. Bad PCV valve.
4. Bad or leaking Brake-booster diaphram.
5. Top casting warped (from overtightening carb onto the manifold, or overtightening the air cleaner stud.)
6. Feedback valve not working.
7. Mixture set too lean.
8. Throttle position sensor not adjusted right.
9. Altitude compensator malfunction.

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1. Float level too high.
2. Power valve leaking.
3. No power or ground circuit up to the idle cut off solenoid.
4. Timing retarded, Vacuum advance not working properly or distributor weights sticky.
5. Excessive exhaust system backpressure.
6. TPS (throttle position sensor) bad or out of adjustment.
7. Bad O2 sensor.
8. Gas in crankcase.
9. Engine oil old or needs changing.
10. Leaking fuel pump diaphram.
11. High fuel pressure.
12. Sticky or plugged PCV valve.
13. Charcoal cannister defective or saturated with gas (Replace it).

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1. Float level a little too high.
2. Main jet a little too big (possible but least likely. Check all other items first.)
3. A little dirt or gum partly blocking the main air bleed.
4. Power valve leaking a little.
5. TPS out of adjustment.

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1. Ignition problem: Usually is occasional plug misfire or marginal plug wire. Also check cap, rotor, and for corrosion at coil terminal. Check centrifugal advance and vacuum advance on distributor.
2. Ignition timing off at cruise. Check distributor for wear & correct operation.
3. Bad or lazy catalytic convertor.

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1. Vacuum leak.
2. Main air bleeds blown out, or missing.
3. Wrong main air bleeds.
4. Main jet much too small, or dirt in main jet.
5. Leaking carb base plate.
6. PCV valve stuck open.

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1. Bad MAP sensor or bad MAF sensor. (Check also any vacuum lines to the sensor.)
2. Main jet too large (possible, but least likely).
3. Main air bleed plugged up with dirt.
4. Float level very high.
5. Very heavy float.
6. Bad power valve or power valve stuck on, or no vacuum to the power valve (hose connected wrong?).
7. Bad or misadjusted TPS.
8. Ignition timing at cruise is incorrect.
9. Plugged exhaust or bad catalytic converter.
10. Sticky or plugged PCV valve.
11. High fuel pressure.
12. Gas in engine oil, or it needs changing.
13. Mixture control solenoid defective (some models).
14. Charcoal cannister defective or saturated with gas. (Replace it)
15. Failure to enter closed loop.
16. Bad oxygen sensor.
17. Restricted air intake.

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