User Question – Decompressor System

User Question from the Cyclepedia General Service Manual topic on Decompressor Systems:
Hi, Great Info. How can you tell if your small engine has a decompressor? Manual, or automatic? Thanks, John

Cyclepedia:

John,

Thanks for contacting us. Decompression systems are most commonly found on single cylinder engines, and usually larger displacement ones. The photo below is an exception of a decompressor system in a small engine. This is from our 2010+ Kawasaki KLX110/L Online Manual. Decompressors are occasionally found on some twin cylinder engines, but are not common on multi-cylinder bikes.

On most modern four stroke engines the decompression system functions by opening the exhaust valve. There are a couple of different variations on this theme.

A weight type automatic system on the camshaft is the most common these days. This will be on the exhaust camshaft if it is a DOHC engine. These parts will not be visible without removing an engine cover. Check the service manual or parts diagrams for your model to see if it has something like this. If your engine has a reverse decompressor system this will be built into the camshaft and not be visible from the outside. Refer back to the original topic (Decompressor Systems) for more information on these systems.

A cable operated decompressor system will have externally visible components. Check for a cable that runs to the exhaust side of the cylinder head. This cable may be activated by a lever on the handlebar (manual) or linked to the kick starter (automatic) as in the example photo from our Honda XR200R Online Manual.