The Ford Barn

Bruce_MO · 05-28-2026, 12:32 PM

Recently restored ‘46 Mercury with a stock 59A motor. It has about 300 miles on it since it was finished. New issue has shown up recently. When cold, it runs very well. When it gets fully warmed up (temp gauge to the right of center, but nowhere near hot), it starts to miss or stumble a bit. Seems to do it on level roads at 25-30mph, and when I just start to decelerate. It usually seems to pull under load just fine with no stumbles. The stumbling is generally pretty faint; doesn’t feel like the motor is cutting out with a “hard” loss of spark. It idles smoothly hot or cold.
The distributor was rebuilt by Michael Driskell, and the coil was rebuilt by Skip Haney. I rebuilt the carb and fuel pump, and I just replaced the condenser with a new NAPA Standard one, thinking that condensers were a likely problem if the issue only occurs when hot. I just snugged up intake bolts and carb mount studs, making sure no vacuum leaks were causing the problem.

Before I start throwing time and $$$ at it, I thought I’d get some opinions. My next step is to swap a friend’s coil to rule that out. Thanks in advance for your suggestions and assistance.

05-28-2026, 12:32 PM	#1
Bruce_MO Senior Member Join Date: May 2010 Posts: 592	Suggestions welcome- ‘46 runs rough when warmed up Recently restored ‘46 Mercury with a stock 59A motor. It has about 300 miles on it since it was finished. New issue has shown up recently. When cold, it runs very well. When it gets fully warmed up (temp gauge to the right of center, but nowhere near hot), it starts to miss or stumble a bit. Seems to do it on level roads at 25-30mph, and when I just start to decelerate. It usually seems to pull under load just fine with no stumbles. The stumbling is generally pretty faint; doesn’t feel like the motor is cutting out with a “hard” loss of spark. It idles smoothly hot or cold. The distributor was rebuilt by Michael Driskell, and the coil was rebuilt by Skip Haney. I rebuilt the carb and fuel pump, and I just replaced the condenser with a new NAPA Standard one, thinking that condensers were a likely problem if the issue only occurs when hot. I just snugged up intake bolts and carb mount studs, making sure no vacuum leaks were causing the problem. Before I start throwing time and $$$ at it, I thought I’d get some opinions. My next step is to swap a friend’s coil to rule that out. Thanks in advance for your suggestions and assistance.