Jon IOW

FYI - as for the mystery adjustment screw on the carb. I set mine to 3 turns out from closed (as a semi-intelligent guess). No idea if this is as per factory, but saw runs great so I guess it doesn't matter.

Good news and long story short - saw is now running like a sewing machine!! The supplier informed me there are actually two rings for the 540XP Mk2 depending on serial number. Unfortunately both products were labelled on their website as being compatible for the Mk2, but did not specify the serials in the description. I only noticed the one ring, not the second. The ring which I purchased was the wrong one according my serial number, I needed the later one. In lieu of this they agreed to send me a whole new piston assembly minus the cost of the original ring. New piston now fitted and straight away the saw fired into life and idled nicely for 5 mins, and revs up nice. Tbh I don't think a ring compressor is necessary for this dinky toy stuff, mine slipped in with a little bit of lube and finger tip encouragement no problem (no pun intended). The rings got naff all resistance and the head is rounded off a little at the end to help ease it in so no drama. I didn't bother to measure the new ring gap, but it was a noticeably closer fit compared to the old worn out one! Lesson learned and case closed. Many thanks for all the advice etc!

The gap on the old ring is approx 0.7mm which according to google is approx 28 thou. Quite a lot! I checked the thickness of the old and new rings and they are actually the same, must have been a trick on the eye! The old ring is 1.5mm. The new ring is 1.7mm. The 0.2mm difference means the new ring needs to sit deeper inside the groove on the piston and seems to be this that's causing a tight fit. Cleaned out the gap with the old ring, got some carbon out but still the new ring is a tight fit. The new ring just won't go deep enough into the groove. And yes I have got the ring in the correct orientation etc relative to the little alignment pin thing. Even a blind man could spot that.

By the way I bought the new ring from L&S engineers: Piston Ring for Husqvarna T540 XP, T540 XPII Chainsaw - 577 96 05 01 | L&S Engineers WWW.LSENGINEERS.CO.UK Piston Ring Husqvarna T540 XP, T540 XPII Chainsaw - 577 96 05 01 Genuine Husqvarna Part. OEM No. 577 96 05-01

Hi guys, Parts arrived today. I replaced all the bits in the carb, all good. I am having some problem with the piston ring though. On opening the new one I noticed it is very slightly thicker and wider than the original. Obviously I put this down to wear on the old one. But I am struggling to fit the new ring. It wants to go in, but I cant squeeze it together and get the gap to close up. I checked the piston, its clean and no obstruction in the gap. The ring does fit in the gap but only like half way inside before it starts to bind. As far as I know the ring should have some small freedom of movement once installed on the piston to prevent damage to the bore. Any ideas? Cheers, Jon

Thanks guys for all the advice! I checked, it is a Mk2. Ordered carb rebuild kit and piston ring this evening. These parts are fairly cheap so worth a try. Will fit those all see what that yields! Unfortunately dealer didn't give me print out of the autotune stuff....seems the norm now everyone wants your money and you get less and less in return!

Thanks for comments. Its 2020 so actually might be a Mk2? Cant remember if it was a mk1 or mk2 when I bought it. Dismantled it this afternoon. Piston and liner look fairly clean, no significant scoring. Ring looks ok too. Took the carb apart to clean it, also looks quite good and clean. No muck on the micro filter but cleaned it anyway. Now I put it all back together I can only get a few puffs out of it, won't run at all. Noticed there is a needle/screw on the carb behind the air filter holder. Looks like a idle speed screw or similar? I removed it to clean it out. Just wondering if this is not set correct? Any ideas how many turns out from closed it should be? I'm reluctant to bin it because its still clean and tidy, must be something simple.

Hi everyone, my 540xp Mk1 giving me problems, can't figure out why. Symptoms are the idle is too low to keep the saw running, after 30 seconds or so at idle, revs gradually drop then it will cut out. It will cut at full power, but a little sluggish to rev up to full speed. Starts fairly easily. Will do this behaviour regardless of hot or cold. I've taken it to dealer, no error codes, latest firmware installed and reset Autotune. Checked impulse line, looks okay, connected both ends. Compression feels strong, but giving 75psi which seems low. However, to compare I checked my 550xp (which runs lovely), and it gives the same, so maybe just my tester. Fuel and air filter both clean. Replaced spark plug. Primer bulb seems to work fine, pumps and refills nicely. Given it a good run for 3-4 minutes at full power cutting to let Autotune do its thing. Any other ideas? Frustrating cos its 90% there, just idle is not quite right and performance slightly sluggish. Like its being starved of air/fuel slightly. Grateful for any advice!

Newnham Road Binstead Ryde Call for details Prefer hardwood Drop off or collection.