Air bubbles in an ECHO trimmer primer bulb.

Its not un common to have air in the primer bulb, Check for a possible air leak in the system. This will make the saw idle higher than normal if its sucking air from elsewhere.

Sounds like you either have a hole in the fuel line or the primer bulb valve is leaking and drawing up air instead of drawing the fuel out the tank

Get the carb kit and replace all. Make sure that you tighten all the screws so there are no air leaks and cross your fingers.
Those cards are a royal pain in the ----

An air bubble may stay inside the primer bulb after starting the motor. But if you see foaming or churning fuel coming into the bulb you may have an air leak in your fuel line. This usually occurs inside the gas tank because the line becomes hardened from alcohol exposure and then the fuel clunk moving the line around causes a split near where the line passes through the tank body. Believe me....the break will get worse and one day you wont be able to keep the motor running. So now would be a good time to size up the fuel line and pick up replacements. You can swap the lines yourself with a little effort and you will save money too. Bonus!

Be safe and good luck!

There is a hole some where check prime bubble

Check INSIDE the fuel tank. It is possible the fuel line inside the tank has deteriorated and the filter broke off. That would cause fuel line to FLOAT in the tank instead of lie on the bottom. This could easily be the cause of no fuel in primer/purge bulb. You probably need to:

Install new fuel filter..........Install new fuel Lines.......Install new primer bulb........Clean carburetor.

So in some respects, you are probably correct....no fuel filter equals bad fuel entering carb (but if none in bulb, doubtful much fuel (dried up maybe ) in carb.

take the carby in to have it assembled correctly
the positioning of the gasket on the right side of the diaphragm is critical

I've been fighting with an Echo PB-251 blower and an Echo SRM-225 string trimmer since near the end of last lawn season (this is the forth season I've had them). Along comes a thread on a firearms forum and lo and behold the answer to the problem is spelled out in terms even I can understand.

After reading that thread (which attributes the problem of the engine bogging down when throttle is activated to collapsing fuel lines) I was going to just replace the fuel lines, but I discovered that there are kits that include new fuel lines, rubber grommets, filters, clips and cap seals for about $13.00 each. Hell, the kit for the SRM-225 even provided a new primer bulb. Ten minutes after the UPS truck delivered them to my door I had both machines running like new again. If you've tried other things and it still hasn't worked I highly suggest you try this.

check fuel hoses for tears as you prime make sure two screws are tight that holds the primer bulb

could be but lets try some other things first
On the carb. you have a primer bulb have you pushed that several times and is there gas in the bulb itself?
Are all of your fuel lines intact and not broken or brittle including the primer bulb?
Are you using fresh fuel mixture?
Be sure your stop and run switch is in the run position.
find your air filter and remove the filter itself
then you will be looking at the inlet side of the carb.opening and a orange choke shutter
Take a thimbles full of mixed fuel and pour directly into the carb opening with the choke off( turn trimmer on its side to do this)
now with everything (except for the filter) set to run try to start your trimmer 4 or 5 pulls
does it try to run? runs and shuts off? if so then you have carb. issues
which you can either replace or rebuild
sometimes if you do not want to tackle it yourself then it is less time consuming to replace it
but not cheaper.

hope this helps you some