Slightly off-topic - 2-cycle blower performance

[HarleyT]

With no pics, it is hard to help.

 

[atpchas]

Can you put up some close up pics of the carb/linkages?
Maybe the throttle cable needs adjusting so the throttle can open fully.

The cable opens the throttle all the way to the stop (true for both carbs).

 

[boltonranger]

I've worked on several blowers and
I don't think you have a problem.

The revs are where they are because of the load being static.

Think of it like this:
A chainsaw that should rev 15,000 rpm only hits those revs until it's in the wood and cutting.

The blower hits the high rpm when the inlet/outlet are covered. Once the blower has to do the work of moving air the rpm drops -- just like when a saw starts to make chips. Make sense?

 

[Stihlhead460]

I think you are right. I own a pb250 and it does the same thing if you get the nozzle too close to something. The revs jump way up. Other than that, it starts quick and easy. Matter of fact my father in law gave it to me after sitting unused with a tank full of rotten ethanol has that was over 5 years old.

 

[undee70ss]

I'm working on an Echo PB-251 blower. I can't get it to run at the maximum RPMs it should (6700-7200 per Echo). It maxes out at less than 5500 RPM unless I put my hand over air output to increase load on engine - then revs increase to more than 7000 RPM. Of course, that defeats the purpose of the blower...
Things I've checked/done:
changed spark plug
checked muff for carbon buildup
pulled little black plug on carb (Zama RB-K90) and adjusted mix
tried a new carb and tried same adjusting
compression is 135psi, no scoring visible through exhaust port
checked fuel lines and replaced fuel filter
run with and without air filter - no change

Anything else I should check?

Have you checked the reeds? With air filter off are you getting any spit back from carb? Pressure/vacuum test crankcase?

 

[atpchas]

Have you checked the reeds? With air filter off are you getting any spit back from carb? Pressure/vacuum test crankcase?

Playing with the very limited options on that model carb, I managed to get the revs up into the high 6000s. I called it good enough and the owner was content.