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Posted by David Sherman [72.47.9.228] on Sunday, February 27, 2011 at 15:46:02 :
We finally got some snow so I decided to give the '56 Sno-Cat a road test. It's always had the best-sounding idle of any of my flat-heads, so I assume the engine is in good shape internally. On the first drive around the block I noticed it was backfiring under load and didn't seem as powerful as it should be (not that I expect much, but this was on the flats on packed snow). I'm figuring either timing or fuel. Engine sound and speed only change a little when I turn the distributor. The timing pointer has been removed from the timing chain cover. There is one mark on the crankshaft pulley, a simple nick in the rim of the pulley, with no other marks near it or anything. Viewed from the front of the engine, it moves from about the 8 o'clock to 9 o'clock position as the distributor is turned from full retard to full advance, with the timing light on #1 wire. This is nowhere near where it should be (near the top or 1 o'clock), but the engine idles great so it must be okay. This is a non-standard pulley, with a normal-sized large diameter "A" belt pulley on the outside to drive the water pump and alternator, and a smaller diameter "B" belt pulley on the inside to drive the hydraulic pump. I'm not sure what it's off of or if it's something special Tucker made.
I will try driving it under load with the distributor turned to various positions to see if I can get it to quit backfiring. The other thing I'm wondering about is if it could be too lean. Usually a vacuum leak makes an engine idle rough, so I doubt there's a leak, but maybe something is wrong with the carburetor. I did rebuilt it a few years ago but haven't been able to put a load on it until now. It's a Carter Ball & Ball. I have had an odd problem with the inlet valve sticking after it's sat for a long time. It's easy enough to pop the top off and jiggle the inlet valve loose, and then the engine starts and runs fine, but it's strange that it would get stuck. There's no visible gunk in there. Still, once it's unstuck, the bowl quickly fills up all the way. I've taken the top off to check. There's no dirt, water, or varnish in the bowl, so it seems unlikely that a jet got clogged.
Any ideas? I'm going to take it out now and futz with the distributor a bit.
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