the terra tiger is a tough machine to do an engine transplant. if you measure from the right side of the engine clutch to the right side of the tub, you'll see how little room you have. i've never found a 4 stroke to put in mine that would make much power and still fit. you might be better off just going to a larger single cylinder 2 stroke. if you do find a sutable 4 stroke, please let me know. i have a 300cc rotax in mine, oil mixed 42:1 with "golden spectro" (from a dirt bike shop). it doesn't make a ton of power, but it moves the tiger along pretty well.
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