912 Running on 2 Cylinders
 

I recently bought a '66 912 and I'm trying to get it running better. It appears that both cylinders on the passenger side are not firing. With the motor running I can pull both plug wires with no change in how the motor runs.

Here's what I've done to troubleshoot it:

Compression Test: All cylinders are 135 or better

Spark: Both plug wires on the "dead" side have spark

took the valve cover off and cranked the motor; Valve train seems to be operating fine

Took the fuel line off the right carb and fuel is present; Changed the carb too (twice)

Any advice is greatly appreciated.

Did you remove mains and idle jets and clean thoroughly .

In keeping with Prsh356’s suggestions, if the car will idle at all, try dripping a small amount of fuel into the suspect carb throats and see if there is an apparent difference in revs. Use only a couple of drops.
If nothing changes, pull the 2 plugs to make sure someone didn’t put the wrong (longer) reach plugs in there which would close the gap. Also double check your firing order 1432 to be certain 3 & 4 aren’t crossed.
Bill

We put a totally rebuilt carb on the "dead" side with very little to no change. We sprayed carb cleaner in the carb when it was running and the revs. went up considerably. I'll triple re-check the firing order. Thank you for your responses.

Plug wires
 

Try replacing the plug wires along with the plug connectors. If the plug connectors have a built in resistor, they may work perfectly with no load, then fail to spark under compression.
Bob B