The 4-Cylinder Nissan H-20 engine in my old TCM forklift. It wasn't running when I bought it, and I was only able to work on it in my spare time when I wasn't busy with customers' machines. The carburetor was actually full of MUD, and the ignition wiring was a bit of a mess, but with some time, patience, and determination I got it running again. It's a bit more challenging than the small 1 or 2 cylinder engines that I normally work on, and the engine compartment is cramped, but it's still a thrill to finally have it purring away at about a 600-700rpm idle. It still needs a PROPER tune-up, but just getting it running is a major accomplishment.