Sneeze/cough at idle

**Gorilla0178** · 06-12-2021, 10:31 AM

So I don't know if its a lean sneeze or something else. Motor is back up and running, its always has a cough at idle, itll be running fine then itll stutter and cough out a puff of smoke, if im in gear at idle it seems to do it and sometimes itll do it and stall out. It starts right back up, if I rev the motor up it seems to clear it up for a bit. Carbs are rebuilt and had CCMS reeds, runs perfect off idle.

**WaterZebra** · 06-12-2021, 02:08 PM

Originally Posted by Gorilla0178

So I don't know if its a lean sneeze or something else. Motor is back up and running, its always has a cough at idle, itll be running fine then itll stutter and cough out a puff of smoke, if im in gear at idle it seems to do it and sometimes itll do it and stall out. It starts right back up, if I rev the motor up it seems to clear it up for a bit. Carbs are rebuilt and had CCMS reeds, runs perfect off idle.

It might be caused by exhaust back pressure stacking up to a point where it interferes with combustion in the cylinders. A very quick way to eliminate this possible cause is to run it on a garden hose where there is no water backed up thru the exhaust system. If it idles forever without stuttering of coughing then the exhaust system isn't breathing the way should. Usually the mid section tower has ports where the exhaust has a shorter path to escape. The ports should be spitting out exhaust and cooling water. If not, then you probably have passages blocked by silt or salt.

**Gorilla0178** · 06-12-2021, 04:54 PM

It does it on the hose and in the water.

**flabum1017** · 06-12-2021, 06:01 PM

Lean spit.... might have to go a little smaller on your idle air jets.

**flabum1017** · 06-12-2021, 06:03 PM

First, do a sync and link..... carb sync is very important.....

**H2OPERF** · 06-12-2021, 09:03 PM

Do as said above, its very important that all 6 carb throttle plates are all closed at idle with a slight gap in the carb roller to throttle cam. a larger gap on the throttle cam will richen up the lowend.