I have a 2001 yamaha wr426 that won't start. It sat for about a year with fuel in it. I got it to start but it wouldn't idle and kept cutting out while I was riding it.
I pulled off the carb and cleaned it out. It still wouldn't start.
then, while I was kicking it, it started to lose compression. I could kick it thru without pulling the decomp lever.
I replaced the plug and changed the oil. The oil smelled like gas.
I put everything back together and the compression was back. I tried to start it but nothing, and the compression was gone again.
I let it sit came back and the compression was there but as soon as I started kicking it, it was gone again.
Any ideas?