D17 lean on #3

[Wingswd]

Working on a 62 Series 3 D17 with a slight exhaust backfire. Plugs show #3 being very lean. wires are new, compression good, head is off and valves are alright. Any ideas and what plugs should it have in it.

 

[old]

If running lean on just one cylinder that almost has to be something wrong with the manifold as in a clog or a crack. Spark plugs will not change a rich or lean condition. Now then a intake valve that does not open as wide as it should would or even an exhaust valve not opening as it should would cause that. As for the back fire that is the by product of it running lean

 

[Wingswd]

Thanks old, I'm just going to keep checking things. Lap the valves, set the valves, get it all back together and hope for the best. As for the plugs I just wanted to make sure I had the right ones in it.

 

[old]

Another thing that could have cause that is a bad manifold gasket and leaking air at the #3 intake area of it

 

[Wingswd]

I thought of that but 3 and 4 share a port

 

[BushogPapa]

At that point, you need to "think like a JD Man".!

All the older 2-cylinder JD's with a Single throat carb has the same problem..
The Leading cylinder Hogs the majority of the inlet charge and the trailing cylinder "Loafs"..
That would not normally be a problem..but..IF you had a leaking gasket...there could end up being a Lean condition..
And, as OLD said..even a worn cam lobe or worn cam bearings could cause these symptoms..

Ron..

 

[BushogPapa]

At that point, you need to "think like a JD Man".!

All the older 2-cylinder JD's with a Single throat carb has the same problem..
The Leading cylinder Hogs the majority of the inlet charge and the trailing cylinder "Loafs"..
That would not normally be a problem..but..IF you had a leaking gasket...there could end up being a Lean condition..
And, as OLD said..even a worn cam lobe or worn cam bearings could cause these symptoms..

Ron..

 

[Wingswd]

Thanks to both that does make sense