Hello, I have a 1940s Cat D2 and am having some problems with the donkey engine. It is running really badly and no amount of fiddling on my part makes any improvement. The engine has good compression and the magneto is good - it will throw a spark when just turning the flywheel by hand. I have pulled the carb apart and given it a good clean, everything seems ok with it. The engine starts fairly easily but it never fires evenly. It misses really badly, so badly that even with the throttle wide open it never get anywhere much over what I would imagine to be idle speed. All the while there are clouds of black smoke pouring out of the exhaust which makes me think there is something wrong with the carb and it is getting too much fuel. The carb is a zenith, I couldn't say which model but if you unscrew the bowl from the side of the barrel there is a long brass tube protruding from the bowl through to the other side of the barrel. Hopefully someone can identify it from this description. There are two fuel mixture screws and I have slowly adjusted both of these in various combinations but they have almost no effect on the running of the engine. I can't imagine much can go wrong with a carb as simple as this one but the black smoke points to this being the problem. I can't think of anything else that might cause these symptoms. Is there anyone else out there who has had experience with these engines and can offer some advice? Any help greatly appreciated.
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