There is a CV25-69513 in my shop that seems to be running rich on cylinder #2.
At first, I just agreed with the customer that it was a fuel system issue, and I ordered both the carb rebuild kit and the accelerator pump kit.
But then I had second thoughts about it and tested it further. I ran each cylinder by itself. #1 is pretty smooth, but $2 is where there seems to be a lot of blubbering/missing/popping going on. So I hooked up my spark tester and ran the engine with the tester in-line. It sparked consistently, and there was no correlation between spark and engine performance problems.
Then I tested the compression. Cylinder #1 (the smooth one that seems fine) had 130 lbs, and cylinder #2 (the bad sounding one) had 165 lbs. A pretty significant difference, so I loosened the rocker arms and did a leakdown check. As you could imagine, there was more leakdown on cylinder #1 (80% actually) than on cylinder #2 (50%). I watched the gauge as I rotated the crankshaft against the pressure. Cylinder #1 was noticeably easier to turn against than #2. The leakage was from the intake valve on both sides, as I could easily hear air escaping through the carburetor (crankcase breather was not mounted, so no air was coming through the breather tube).
The funny thing about all this is that when the engine runs, cylinder #2 sounds like it's the problem. However, it's clearly the stronger of the 2 cylinders. Which leads me to think I really do have a carburetion problem. Because if compression were the problem, it would run better on #2 than on #1, which is backwards from what it is really doing. It has been running rich, with the spark plugs looking pretty black and sooty.
I'm thinking we really do have a carburetor problem, which was causing the customer to complain. But I'm thinking there's an unrelated compression issue as well that the customer didn't notice.
What do you think?