So I picked up the subject saw as a gift for a friend and broke it down for a thorough cleaning, also replaced the impulse, fuel and oil lines & filters, dressed the bar and sharpened the chain (RM3). Compression is ~135psi. The saw was running when I bought it but not well. Idle was way too fast and WOT RPM far too low. The carb is aftermarket but the original carb was included as well. I didn't touch this carb aside from resetting the needles to 1 L, 3/4 H per the manual. Well it started up after only a few pulls and seemed to idle fine after a warm up and adjusting the LOW and idle screws. Onto the HIGH I tuned it to ~13.5k RPM (manual states 14k), but this took ~ 1/2 turn out to get there from the original 3/4 turn. At that time I thought it's probably because of the aftermarket/cheapo carb. Well it actually cut pretty well for only being a 40cc saw. After cutting for about 15 minutes though I started to notice the idle surging some between cuts. It never surged at higher RPMs though. No amount of adjustment would stop it so I stopped and rechecked RPMs. Low was varying between 2000 and 3300 rpm, high was right below 14k.
I've dealt with air leaks before, both on crank seals and carb boots, and it's always been high RPM surging or varying WOT RPMs over time. Could this just be a simple carb issue? Could the extra 1/2 turn on the H screw be accounting for a leak somewhere? I have purchased a Zama rebuild kit for the original carb and am hoping to work on that this weekend and retest but was hoping for some experienced feedback into what else could be going on. What else should I be looking at?
I've never done crank seals on a clamshell saw before but will if that's the issue. I take it these have to be "placed" in while it's split and can't be pressed in? Also, does the block have to be removed to replace the carb boot?
Thanks in advance for all the information!
I've dealt with air leaks before, both on crank seals and carb boots, and it's always been high RPM surging or varying WOT RPMs over time. Could this just be a simple carb issue? Could the extra 1/2 turn on the H screw be accounting for a leak somewhere? I have purchased a Zama rebuild kit for the original carb and am hoping to work on that this weekend and retest but was hoping for some experienced feedback into what else could be going on. What else should I be looking at?
I've never done crank seals on a clamshell saw before but will if that's the issue. I take it these have to be "placed" in while it's split and can't be pressed in? Also, does the block have to be removed to replace the carb boot?
Thanks in advance for all the information!
