Echo CS-400 Chainsaw Parts and Fitment

The air filter also turns up under 90155, 90109 and 90155Y - four numbers, one filter. That pattern repeats across Echo's range and is worth checking before deciding a listing is wrong.

Echo's own chain for this class is 91PX57CQ - 16 in, 3/8 in low profile pitch, .050 in gauge, 57 drive links - and it lists the CS-400 among its fitments alongside CS-303T, CS-310, CS-330MX4/T, CS-3510, CS-352, CS-353ES, CS-370 and CS-400F. The full cross-reference is on the chains and bars page.

The complication is that Echo also ships the CS-400 with an 18 in bar in some packages, which needs a longer chain at the same pitch and gauge but 62 drive links instead of 57. The two bars are not interchangeable with each other, and a chain bought for the wrong one simply will not tension. Count the drive links on the bar you actually have, or measure the bar length stamped near the mount, before ordering - the model name alone does not tell you which one your saw carries.

The CS-400 runs the same 50:1 Power Blend mix as the rest of Echo's handheld two-stroke range - see Echo 2-stroke oil and the 50:1 mix. Bar and chain oil is a completely separate product and never goes in the fuel tank; running the saw with an empty oil reservoir ruins the bar and chain together, usually within a single tank of fuel.

If the saw won't hold a tune, the cheap parts fail first: stale fuel, then the air filter, then the fuel lines and primer bulb, then the spark plug, and only then the carburetor. The full logic behind that order - and why it is rarely actually the carburetor - is on the Echo carburetor page.

The CS-400 takes the same NGK BPMR8Y plug as Echo's trimmer range - see the Echo spark plug page for the exact number and the Champion cross.

The genuine Echo bar and chain oil numbers - 6459007 for the gallon, 6459012 for the quart - are on the bar and chain oil page.

Echo sold this 40.2 cc engine under three model numbers - CS-370, CS-400 and CS-420ES, plus the "F" front-handle variant of each - and the carburetor, filter, starter and ignition coil all cross freely between them. The same engine was also sold through Shindaiwa, Echo's sister brand under the same parent company, as the 402S - the reason Shindaiwa part numbers turn up in CS-400 carburetor listings.

What does not cross is the bar and chain length covered above, and the chain brake assembly, which is specific to the 370/400/420 shroud shape rather than the engine. If the starter cord pulls with no resistance or will not retract, that is the recoil assembly above, not the chain brake - see the full distinction on the recoil starter and pull cord page.

Echo also sells a smaller, cheaper tier below this one - the CS-310 and CS-352, at 30.5 cc and 34.1 cc. Neither shares a single engine part with the CS-400/370/420ES family above; they run their own carburetors and filters entirely. See the CS-310 and CS-352 parts page for those numbers.

One size up from this 40.2 cc engine, the CS-490 and CS-590 Timber Wolf are a separate platform again - different carburettor, filter and chain pitch - so nothing on this page carries across to those larger saws.

At the opposite end of the chainsaw range is the top-handle Echo CS-2511T, a 25 cc arborist saw with a Walbro WT-1208 carburettor (A021004690) and a 12-inch bar - a different platform again from the rear-handle CS-400.

A CS-400 that cranks but never fires with no spark at all needs a different part than anything covered above - see Echo ignition coil numbers by engine, A411000264 for this family.