Flowing the Carb Jets

A while back I realized that the engine was idling really rich, even with the adjustment set as lean as possible.  It seemed to be so rich that the #1 cylinder was not even firing most of the time.

So a couple of days ago I removed the carb jets (a 10-minute operation) and flow-tested them.  This involves connecting the jet via a plastic tube to a water reservoir mounted exactly 36″ above the jet, and measuring how rapidly water flows out the jet.  I threw together a test rig that resembled a hospital IV setup (or an enema bag) using a plastic gallon jug, some rubber and vinyl tubing, etc.

It turned out that the idle jet was way oversize, and was flowing  60% more than spec.  The main jet flowed about 40% under spec.  These were reproduction parts installed by a previous owner, and clearly they were not made to OEM specifications!

The fix was to solder the jet openings closed and re-drill the openings to the correct size.  This involved a bit of trial-and-error, re-testing the flow rate and trying different size drill bits.  I re-installed the jets (another 10-minute operation) and afterward the engine ran much better, firing evenly on all four cylinders.