1988 70 Yam overheating (head or too lean??)

I have a 1988 70 yam that is overheating and tripping alarm at high RPM, above 4200 rpm. I replaced water impeller with kit. Motor runs all day under 4000RPM. Thermodisc tested ok. Compression is 130psi top,125psi middle, 122psi bottom. I was told could be possible head gasket or Carbs too lean. Ran motor until alarmed checked compression still around 125psi but plugs looked dry and alittle white/brown. Checked plugs after running at idle and they looked wet and dark. Could this be a cracked head or gasket or Does it seem to be running too lean. How can I determine a faulty head or gasket. Can I run 50:1 gas mixture and plug oil pump to check if it is working properly? How do i know if the carbs are too lean. The motor idles perfect. It seems like it has a very slight miss after running.<br />Thanks for the help

Re: 1988 70 Yam overheating (head or too lean??)

hello<br /> leave the oil pump alone. if after replacing the tstat and water pump the symtoms you describe are usually head gasket related. remove the head and have it surfaced. clean the block carefully. I use the drill mounted pads from 3-m. use a pick and scrape all the debris from the cooling system passages. then retest. just hope no impeller pieces are lodged in the exhaust cover.<br /> good luck and keep posting

Re: 1988 70 Yam overheating (head or too lean??)

Should I pull the inner and outer exhaust cover along with the head to check for blockage or water leaks. Thanks for the reply