I have a zd331 that runs rough at idle and has a lack of power under load. A little history, the engine overheated last year and the head was cracked. This was replaced. At idle it runs rough but half throttle smoothes it out considerably. Operator say it does not have power in taller grass. Its a 72" mulcher deck. Are there some visual symptons or simple tests I can do to help me eliminate the possibilty of poor compression in one of the cylinders? It is not burning or using oil. MY kubota tech says it sounds like a fuel delivery problem. So far I have changed both fuel filters, new inner and outer air filters, pulled fuel lines off at fuel selector and blew compressed air towards fuel tanks and the diesel in tank bubbled noticeably. Don't know if thats enough or if I should take tanks off and inspect pick up line and filter inside tank, if there is filter in there. I took apart fuel selector, big mistake, the o rings were damaged but now having trouble putting it back together with new o rings that I got from my metric o ring kit. Dealer says you cannot buy just the o rings so I ordered a new fuel selector, holy **** 165.00, Kubota I tell ya. Anyways tommorow I will install new fuel selector and a new fuel pump I have in stock. Don't know what else to do, sorry to be so long winded but any help would be appreciated greatly, thanks.