The Ford Barn - View Single Post - ‘39 Merc hesitating under load...driving me crazy

Tinker · 07-12-2018, 12:36 AM

fluttering vacuum readings shows sticking valves. If the vacuum drops quickly and then comes back up, it may just be one valve. try some mmo in the gas and do a couple treatments of pouring some mmo down the carb till it smokes out. Worth a shot. Maybe a burnt valve but your compression readings are good. Sticky valves will run havoc under load but running in the garage sitting you wont tell.

Vacuum at idle should be around 19. 22 isn't an issue to your problem and you can adjust the carb idle screws to lower that easily.

07-12-2018, 12:36 AM	#2
Tinker Senior Member Join Date: May 2010 Location: MN Posts: 7,053	Re: ‘39 Merc hesitating under load...driving me crazy fluttering vacuum readings shows sticking valves. If the vacuum drops quickly and then comes back up, it may just be one valve. try some mmo in the gas and do a couple treatments of pouring some mmo down the carb till it smokes out. Worth a shot. Maybe a burnt valve but your compression readings are good. Sticky valves will run havoc under load but running in the garage sitting you wont tell. Vacuum at idle should be around 19. 22 isn't an issue to your problem and you can adjust the carb idle screws to lower that easily. Last edited by Tinker; 07-12-2018 at 12:47 AM.