The motor in question is late 70's to early 80's vintage. Starts fine, idles well, but refuses to rev higher than trolling speed, even at full throttle. Fuel does not seem to be the culprit ,plenty of bulb pressure. Checked the filter and mix, supplied fresh gas. Only visible problem is that the top spark plug -both new- gets fouled with oily gunk after only a few minutes of running, bottom plug is not affected. Any suggestions would be greatly appreciated.
