1973 evinrude not running smoothly

I have a 1973 evinrude 25hp. I had a marina mechanic do some work on it last year and he said it was a good motor and never to sell it. Well I am selling it because I have a bigger one now and I dont need it. He replaced the plugs, cleaned and tuned the carb, and replaced the impellor. He also said not to mess with the lean/rich knob because he had it set right. Since then I have messed with it because I was stranded once on the lake. Right now it will run for about three seconds and then it will make a "clunk" sound, almost like it is missing or not getting fuel for a split second. Then it will run fine for a couple seconds and then make the "clunk" again. Any help would be nice. Is it something simple? Could it be something to do with the lean/rich setting? Since the mechanic told me it was a good little motor, that leads me to believe that it isn't a major problem. Thanks for any help.

Re: 1973 evinrude not running smoothly

Sounds like ya' got the lean/rich needle run in a might far. Back it out a quarter to a half turn and see if the cough goes away.

Re: 1973 evinrude not running smoothly

It kind of depends on that clunk sound. If it has a metallic sounding clunk then something has gone horribly wrong. If it's more of a gasping thunk, then it's probably a fuel system problem. Your first step is to do the three things that any tech would do before trying to randomly fix it:<br /><br />1) Compression test<br />2) Check the gear oil<br />3) Check for ignition spark<br /><br />If that's all looking good, then start by adjusting the carb like OBJ suggested. From there you start at the fuel in the tank and work your way through the fuel system all the way to the reeds. If that doesn't fix it...Junk it. It's 33 years old and not worth the aggravation. Average value on that engine is $400.00 in good running condition. The problem is that it's so old that everything is subject to "just going bad due to old age."