Home Grown CBX Leakdown Testing John from Hawaii

As you both suggested, my little "hot dog" compressor just needed a bigger tank to be effective. Picked up the tank today at NAPA, then a bunch of brass fittings and air hose couplings. Just bolted it all together, and voila, works like a champ! And others that suggested checking for air leaks in the system? Bingo, another hit...found that a few fittings had loosened up on the compresor, so double checked everything today so it is really air tight.

And now that little hot dog compressor will fill the 11gal airtank up to 110psi, no problem...altho it does take a whoooole lot longer than just filling the original tank. But the best news is I can now do the leakdown tests on even the leaky cylinders at 100psi, which makes it much easier, here's what it looks like now, 100psi incoming on the left gauge, leakdown shown on the right:

(5K image of leakdown gauges^) More full size images to the images list soon.

And the hissing on all three of the low cylinders is coming from the same place.........out the exhaust ports! So maybe I just have a bit of carbon trapped in there, hope so. Old trick we used to try was rapping the end of the valvestem with a hammer, force the valve off the seat and let it slam back...this would sometimes dislodge carbon or let whatever was stuck under the valve get away and help the valve seat properly.

Just for fun, on Cyl#2 which had a leakdown of about 97/100, I tried to see if I could hear where that one was leaking. Barely discernable, but the hissing is coming through the crankcase! Couldn't hear a thing by the dipstick hole, but just happened to have the alternator off of the motor, and that hole inside that leads down to the lower part of the engine? Right there I could hear a very faint, soft hiss. On the three bad cylinders, you could hear the hiss 20' away, it is that loud and noticeable.

Anyway, more testing to come. I want to do leakdowns on the "almost new" (10K Silver '79) and on JOYOF6, and compare conventional compression readings to leakdown results. And since I'm racing JOYOF6 each week, we can compare effects of leakage and low compression on horsepower...I already know JOYOF6 has some awful compression readings, last time several were below 100# and a couple cylinders below 80#. But I don't say anything to her, she just happily runs 12.0's and high 11's all night long and sounds like the motor is brand new fresh. Can't help but love that bike!

Time to load up, take JOYOF6 to the strip, uncork that sweet six and let her sing all night long!