Recently acquired a 14ft alum boat with a Johnson 25(1981-82)model. The motor will not idle. The initial start up, I use the choke and runs fine full throttle and will get up to 26 mph. When I slow down, twisting back to idle, it dies. I have to twist full trottle in order to start it again. It was doing this before the guy put it up for over a year. Any suggestions? I can change oil, sparkplugs, general mechanical stuff, seems to be an adustment on the carberator... THANKS!