73 25hp Johnson stumbles and dies at 1/2 thrrottle

[airrichy]

1973 Johnson 25 hp elec. start ,hand tiller ran great this spring but this fall started but ran very rough on just one cyl. Found the two wires from kill switch had the isulation rotted off and were shorting together. reinsulated these wires and now motor starts and runs good at idle to 1/2 throttle then stumbles and dies. Will run all day at just below 1/2 throttle and runs smooth. Has 3 new coils, plugs new, points/cond new, fuel tank and fuel line 2 years old. fuel pump sprays strong stream when cranked. New carb kit installed. Carb was overhauled 2 years ago but put in new kit anyway even though carb was spotless when tore down. Fresh fuel in tank. put new ends on fuel hose. I have 7 outboards in all sizes and have maintained them for 35 years so I am not a novice but I am totally stymied at this point please help!

[boats.net]

Run a compression test, check for spark when engine dies.

[Rebel Sympathy]

Is the ignition plate advancing as you twist the throttle handle? Make sure linkage has not come loose.

Also, these 25s ('73 - '76) were a little prone to wearing out the magneto plate. Then, things get sloppy under the flywheel and don't work well until the plate is replaced. The old breaker-points plates lasted much longer. Mike