Ring wear signs? Compression readings if you trust your gauge.
I'd like to see about 15~20 psi more than what your pic shows.
My pb-413 & pb-500 backpacks are in the 155~160 psi range and don't show oil oozing.
my pb-620 was in the 130's range and it was oozing oil.
Will the blower idle at 2700 rpms or does need to be at 3800 to stay running?
aside from carb/fuel issues, low compression can cause troubles with not being able to get a proper low idle speed.
Low comp will definitely cause loss of power at top rpms, so that's why I wondered about your max rpm reading with the spark screen and tubes.
But fuel issues will too.
A clogged fuel tank vent or fuel filter can negate your carburetor work.
I've had fuel filters in the blowers that would cause a loss of revs after a few mins of running. Loosening the fuel cap will tell if it's a vent problem (revs will slowly recover) but a fuel filter will still cause rpm loss, even with the cap off.
For curiosity, I shot carb cleaner through one of the fuel filters and blasted air through it... still didn't help. New filter, end of that problem!
The backpacks have a fairly long fuel hose, so it can take a moment to drain it to point of slowing the engine.
To actually physically inspect the rings, of course you'll need to remove the cylinder and remove the rings from the piston.
The rings will need to be inserted back into the cylinder. Use the piston top to push them squarely in the bore.
You need to have the ring in its running area of the cylinder for this.
The ring gap at the ends needs to not be to large.
Wiseco web site calls for .004"~.005" per inch of cylinder bore.
http://www.wiseco.com/FAQs.aspx
Assuming a cyl bore of 1.34" (per the Echo pb-250 owners manual)
https://www.echo-usa.com/getattachment/f44e3018-5220-459d-92cb-6bf526dc7ee9/PB-250LNes_111226_031413
Then minimum gap would be about .007"
The Echo doc doesn't give a minimum gap spec, So just using the Wiseco info.
Echo shows maximum gap of .020" in this service supplement, for the 1.34" bore.
echo-usa.custhelp.com/app/answers/detail/a_id/1714
Also when you have the rings out, look at the width and thickness/height of the rings. If you can visually see a narrowing of the ring in any area, It's worn out.
The Echo service supplement only specs the ring gap and thickness (image G & H , near the bottom of document)
The ring gap will show wear long before you can spot it from looking at the ring for narrowing, So Echo doesn't bother with width dimensions.
Notice there is also a spec for clearance between the ring and the sides of the ring grooves of the piston (image E).
I tend to only be online at irregular intervals, So please forgive me if I'm slow at spotting any later questions.
