There were no engine differences for XLH vs XLCH in 1973 up at all. The only way to tell an XLH engine from an XLCH engine is to look at the engine number. The XLH engine number is going to start with a '3A' designation. The XLCH engine number will start with a '4A' designation. 1971 and earlier had a 2.2 gallon gas tank. In 1972-73 customers had the choice of either a 2.2 or 4 gallon gas tank, making it harder to differentiate the models.