16
TROUBLESHOOTING CARBURETION
POINTS TO CHECK FOR CARBURETOR MALFUNCTION
TROUBLE
CORRECTIONS
Carburetor out of adjustment ...............................
3-4-11-12-13-15-20
Engine will not start .............................................
1-2-3-4-5-6-8-9-10-11-12-14-15-16-17-19-21-24-25
Engine will not accelerate ...................................
2-3-4-5-11-12-19-24
Engine hunts (at idle or high speed) ..................
3-4-8-9-10-11-12-14-20-21-24-26-27
Engine will not idle ...............................................
3-4-8-9-10-11-12-13-14-18-20-21-22-24-25-26-27
Engine lacks power at high speed .....................
2-3-4-6-8-10-11-12-15-18-19-20-21-24-25-26
Carburetor floods .................................................
4-7-17-21-22-25-26
Carburetor leaks ..................................................
4-6-7-10-17-18-23-24-25
Engine overspeeds ..............................................
8-9-11-14-15-18-20
Idle speed is excessive .......................................
8-9-13-14-15-18-20-25-26-27
Choke does not open fully ..................................
8-9-14-15
Engine starves for fuel at high speed (leans out)
1-3-4-5-6-10-11-15-16-17-18-19-21-25-26
Carburetor runs rich with main adjustment .........
7-8-9-11-14-17-18-19-21-25-26
needle shut off
Performance unsatisfactory after being serviced1-2-3-4-5-6-7-8-9-10-11-12-14-15-16-17-18-19-20-
21-24-25-26
16. Clean carburetor after removing all non-metallic
parts that are serviceable. Trace all passages.
17. Check inlet needle and seat for condition and
proper installation.
18. Check sealing of welch plugs, cups, plugs and
gaskets.
19. Check fuel pump operation pump element, inner
and outer one way valves.
20. Adjust governor linkage.
FLOAT CARBURETOR CHECKS
21. Adjust float setting.
22. Check float shaft for wear and float for leaks or
dents.
23. Check seal for fuel drain or bowl gasket.
24. Is carburetor operating at excessive angle?
CHECKS FOR DIAPHRAGM
25. Check diaphragm for cracks or distortion and check
nylon check ball for function.
26. Check sequence of gasket and diaphragm for the
particular carburetor being repaired.
27. Check spring tension on idle governor (if present).
1. Open fuel shut off valve at fuel tank. Fill tank
with fresh clean fuel.
2. Check ignition, spark plug and compression.
3. Clean air cleaner service as required.
4. Dirt or restriction in fuel system clean tank and
fuel strainers, check for kinks or sharp bends.
5. Check for stale fuel or water in fuel. Fill with fresh
fuel/oil mixture of correct ratio.
6. Examine fuel line and pick-up for sealing at fittings.
7. Check and clean atmospheric vent holes.
8. Examine throttle and choke shafts for binding or
excessive play remove all dirt or paint, replace
shaft.
9. Examine throttle and choke return springs for
operation.
10. Examine idle and main mixture adjustment screws
and O rings for cracks or damage.
11. Adjust main mixture adjustment screw. Some models
require finger tight adjustment. Check to see that
it is the correct screw.
12. Adjust idle mixture adjustment screw. Check to
see that it is the correct screw.
13. Adjust idle speed screw.
14. Check position of choke and throttle plates.
15. Adjust control cable or linkage to assure full choke
and carburetor control.
Summary of Contents for AH520 -
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