Echo PB-251 blower won't hit max RPM

[atpchas]

I realize it's off-topic but it is a 2-cycle engine and the issue may pertain to saws. I'm working on an Echo PB-251. It has one of the rotary carbs I hate if they don't run well - no standard high-low-idle settings. The issue is this. The max RPMs I can get is about 55-5600, spec says should do 7000 or so. If I obstruct the blower tube, RPMs do go up to 7-8000. The arrestor screen is spotless but it does have a cat in the muffler.
I'd appreciate any suggestions about what might get me the missing 1500 RPMs. Thanks!

 

[cscltd]

does it have blower tubes on when testing? Will get lower rpm will tubes off. have U adjusted carb?

 

[atpchas]

does it have blower tubes on when testing? Will get lower rpm will tubes off. have U adjusted carb?

Blower tube is on. Carb is a Zama rotary type. It has adjuster screws but they don't have much effect, maybe 1-200 RPMs, not the 1500 I'm trying to get.

 

[cscltd]

Exhaust port plugged?
if not, you may have a carb issue

 

[atpchas]

Exhaust port plugged?
if not, you may have a carb issue

As noted initially, arrestor screen is clean. I've since gutted the cat in the muffler and picked up a couple hundred RPMs. Behavior is identical with two different carbs.

 

[Bronco]

Yes, ditch the arrestor screen.... But Chk the muffler... I have 2 older ones -(PB251) and they were very heavily restricted, like amazing they even turn over. After serious gut job, and retune, at least mine were tuned into oem factory specs in RPM, hi/lo etc... they are over 8 yrs old and still fire up on 1st/2nd pull every time, cold/hot doesn't matter, every single time.