I picked up 2 js550's from 2 different people and they both have the same problem. Hopefully someone on here can point me in the right direction. They crank over very slowly. I put new batteries on them, checked all the connections, and checked the batteries and cables with a multimeter. Everything checks out fine. If I pull the spark plugs the engines will spin like crazy. The only way I can get them to start is to jump them off my truck batteries. Even then, they just barely spin fast enough. The previous owner of one of them said that he milled the head .035", but the other previous owner said he did not know about any mods. Could the increased compression cause this problem? If so, how do others overcome this issue. Any suggestions are appreciated.