Important: Before attempting carburetor diagnosis as outlined below, all other engine systems must be operating properly. Diagnosis of these systems (electrical, exhaust, mechanical, and in the case of fuel economy, odometer accuracy) should be done first. The numbers 1, 2, and 3, are the order of probability. The * indicates additional possibilites.
| HARD COLD START | COLD DRIVE AWAY | HESITATION | ACCELERATION FLATNESS | STALLING | ROUGH IDLE | ECONOMY | FLOODING | SURGE | LACK OF HIGH SPEED PERFORMANCE | HARD NOT STARTING | |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 1 | 1 | Driver habits (instruct owner on proper procedures) | ||||||||
| * | * | * | Check choke rod adjustment | ||||||||
| * | * | * | Check vacuum brake adjustment | ||||||||
| * | * | Check thermostatic choke rod adjustment | |||||||||
| * | * | Check choke unloader adjustment | |||||||||
| 2 | 1 | 2 | Check choke valve and linkage, binding or stuck | ||||||||
| * | 2 | 3 | Air valve binding, stuck, wrong spring tension adj. | ||||||||
| * | 1 | * | Check air valve lock-out adjustment | ||||||||
| * | Air valve dashpot binding, sticking, or stuck | ||||||||||
| * | * | * | Secondary metering rods bent, wrong | ||||||||
| * | Secondary baffle plates missing | ||||||||||
| * | * | * | Secondary main discharge nozzles plugged or dirty | ||||||||
| 3 | 3 | 3 | * | Power piston stuck or binding | |||||||
| * | * | No vacuum to power piston | |||||||||
| * | * | Primary metering rods altered, bent, or wrong part | |||||||||
| * | * | 1 | Check accelerator pump rod adjustment | ||||||||
| * | * | 2 | Accelerator pump circuit dirty, plugged, or inoperative | ||||||||
| * | * | * | * | * | Throttle return check misadjusted or leaking vacuum | ||||||
| 3 | * | * | * | * | Fuel pump pressure or volume not to specification | ||||||
| 1 | 1 | Check slow idle adjustment | |||||||||
| 2 | Check fast idle adjustment | ||||||||||
| * | * | * | * | * | 1 | * | Primary metering jets plugged, loose, wrong | ||||
| * | * | * | * | * | 2 | * | * | Float sticking or level misadjusted | |||
| * | * | * | * | 3 | * | * | Float bowl porous, cracked, etc | ||||
| * | * | * | * | * | * | Throttle body to float bowl screws loose | |||||
| * | * | * | * | 1 | 2 | 3 | Float needle leaking or diaphragm ruptured | ||||
| * | * | * | * | * | * | Idle compensator not opening or closing | |||||
| * | * | * | 2 | Idle vent improperly adjusted | |||||||
| * | 3 | Idle passages plugged or dirty | |||||||||
| * | * | * | Crankcase vent valve plugged | ||||||||
| * | * | * | * | * | * | Fuel filter in gas tank plugged | |||||
| * | * | * | * | * | Fuel filter in carburetor plugged or dirty | ||||||
| * | * | * | * | * | * | * | * | Air cleaner element plugged | |||
| * | * | * | * | * | * | Hole in fuel pump suction line | |||||
| * | 3 | * | 2 | 2 | * | 2 | Check auto trans adjustment | ||||
| 3 | Heat riser valve stuck open or closed | ||||||||||
| * | * | * | 3 | * | * | * | Secondary throttle valves sticking open | ||||
| 1 | Check for full throttle position at carburetor |