The 18 and 20 hp vanny's share the same block... only difference is the carb and intake. Swap them out and gain an instant 2 HP. Also, remove your exhaust manifold and you should find a little steel sleeve in each exhaust port. Rip them out with a pair of needle nose pliers. They restrict exhaust flow. Also building a 2 into 1 header with a better flowing muffler will make a huge difference in how the engine breaths. The vanny's seem to like about 17 inches on each tube before they come together at a collector and go into the muffler
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