Recently picked up a 1969-1972 18-25hp engine (still nailing down the specifics). But for sake or discussion we'll assume 18hp. I got a bit to mess with it after work. Seller said good compression and spark. Compression is good and even. And it did indeed have spark on both cylinders. It did fire up. Pumps water good. Though after a 30seconds or so it acts like it runs out of gas and putters out. Took the carb off. Someones been there before as it's had evidence of being recently " cleaned". Main jet and bowl where clean. Though the idle mixture adjustment is kinda gummy and the little oring on the needle is a damaged.
I noticed It would also go between running smoothly on 2 and occasionally it would miss. And intermittently run on 2. Then smooth back out. It does seem to do this worse as the engine begins to putter out. Checked spark and its nice and bright on one cylinder. And it's not as bright on the other. Ones a bright blue. And the others a dimmer purple ish color, but both seem consistent. On a points ignition whats more likely to cause the dimmer spark?
I noticed It would also go between running smoothly on 2 and occasionally it would miss. And intermittently run on 2. Then smooth back out. It does seem to do this worse as the engine begins to putter out. Checked spark and its nice and bright on one cylinder. And it's not as bright on the other. Ones a bright blue. And the others a dimmer purple ish color, but both seem consistent. On a points ignition whats more likely to cause the dimmer spark?