What size chain does the Poulan Pro 4218 use?

There is no problem as long as the bar is the right bar and the new chain you use is the right pitch for the sprocket that is on your saw.

Three things you need to know to get a new chain, the pitch, the gauge and the drive link count, some of this information should be on the bar itself, if it has 91 stamped on it, it will be a 3/8 pitch 050 gauge, 18" is normally 62 drive links, so the chain is a 91sg 62e

I am pretty sure this machine ran a .325 pitch chain, so the file size is 3/16, if it is running 3/8 low profile chain ( 91 ) it will be a 5/32 file, the pitch should be marked on the bar .

Check to see if you have the chain oriented correctly - it is east to put them on backward without realizing it. Th3e teeth should point forward, with the anti - kickback lug in front of the tooth. Let me know if this helps!!

have you made sure that chain pitch and gauge are the same as the sprocket pitch pitches can be 3/8 lo pro 0.50 gauge

.325 x 0.50 gauge , .325 x 0.58 gauge

3/8 std x 0.50 or 3/8 x 0.58 gauge or 3/8 x 0.63 gauge

you could even have the correct drum but wrong rim sprocket on it

worst case is you could have mismatch bar and chain

make sure that bar adjjuster assy is working correctly

recheck chain / sprocket pitches and bar pitch and groove
gauge

be sure that you fitted chain to rim on sprocket correctly when you fitted bar and chain?

is the clutch cover pulling down tight ?

have a look and let me know if and what you find

cheers paul

Remove the new chain and compare it against the old one. Do the new drive teeth match the 'pitch' of the old chain? If incorrect, the chain cannot be adjusted properly and will 'climb' over the sprocket due to the chain teeth not matching the teeth on the drive sprocket. Getting the proper chain is the answer in this case. Hope this helps!

a pouland pro is a (low h.p. saw) and at 46cc i wouldn't run bigger than an 18 inch bar , its asking to much from the clutch and motor

The chain is directional, only cuts one way. If a new chain won't cut, it must be on backwards.

I have a Poulan Pro 295 20".  When I bought it I also bought a 16"bar and chain and have been using those since.  They make the saw much easier to handle and are a better match to the available power. The key dimension is from the bar's mounting hole to its end.  At the store look at the normal replacement bar for your 18" saw, and pick out a 16" or even 14" bar with the same dimensions there.  This can be easily seen by laying one bar over the other.

I have a 42 cc 14"bar will not start. poulan chain saw.