Tank pressure was positive. Blew stuff out when opened. Vent seems to function as a one way valve, lets air in but won’t let fuel out. If it worked both ways the tank would leak when turned on its side.
Would a bad coil cause my problem? Enough fire to allow idle but spark getting killed by compression when you throttle up?
Thanks you for your earlier reply. Much appreciated….
From what I understand when there is positive pressure it usually happens on hot days when through vibrations the fuel vaporizes in the tank and creates positive pressure.
But...I am working on a 562xp...the carb is starting to piss me off. Purge bulb is sucking air, I pump it up many times and nothing, however when I open the tank it releases pressure (positive), if I pull off the carb, the fuel line starts wizzing everywhere (like a little boy when you change their diaper, pull it off and they turn into a water fountain!!). I bypass the carb with the purge bulb and it cycles fuel like a champ from the fuel line back to the tank with no positive pressure afterwards. I don't think you have this issue since you don't have a purge bulb...but these are the only two instances I know of that cause positive fuel tank pressure (or overpressure).
Does your tank vent look like this?:
You might try popping it off and try running your saw, see if anything changes in how it runs. If it does change and the saw runs better, I would replace the vent, if nothing changes, then the vent is fine. My opinion, I don't think the coil is the issue, however, you can verify that the gap is correct and maybe even clean it off if there is any grime and build up on it.
Otherwise, things I would check: 1) fuel filter, 2) fuel line - pinches, holes, 3) take a look at carb diaphragms and inner parts for gunk or buildup. Also, make sure any vent holes on the carb are clear, some times these get clogged or fines get in and sit on the diaphragms causing issues too.
