Carburetors, Inspecting the carburetor, Carburetors inspecting the carburetor – Cub Cadet MTD P71 Series User Manual

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Carburetors

Troubleshooting the carburetor is a process of elimination. If everything else on the engine checks out, the carbu-

retor is probably bad.

NOTE: It is important to perform a compression or leak down test before condemning a carburetor. An engine

can have a borderline compression reading and not create enough of a vacuum to draw in a sufficient
fuel/air charge.

NOTE: If the engine has border-line compression, a quick test to see if that is the problem is to remove the

spark plug. Squirt a little bit of oil into the combustion chamber to seal the rings. Reinstall the spark
plug. If the engine starts and runs OK, then that was the problem. If it does not start, move on to the
carburetor.

Inspecting the carburetor:

Remove the float bowl and check for dirt and/or varnish.

Inspect the needle valve and needle valve seat for dirt and/or damage.

Inspect the gaskets and O-rings for damage.

Inspect the vents and orifices, verify that they are free of debris.

NOTE: If a little cleaning and new gaskets will fix the carburetor, do it. If the carburetor requires extensive

cleaning it is better to replace the carburetor.

IMPORTANT: Never try to mechanically clean orifices. That will damage them and ruin the carburetor.

NOTE: The carburetors used on all vertical shaft engines are similar in design, but differ in calibration.

NOTE: The jet markings (if present) may be used for identification purposes, but the technician should not

attempt to infer orifice sizes from the identification numbers.

NOTE: Installing the wrong main jet, or a carburetor with the wrong main jet will produce performance and

emissions issues.