I have a persistent throttle up/down on carb- cleaned (was like new inside) and still did same. I have a exact replacement off a 21hp kawi that ran perfect..until rod went that is..but carb worked perfect. appearence is identical..will the 21hp one be to low of jets or do you think same jetting between the two? 21hp is FH640V..and 23hp is FH680V. thanks! Geno.