bad miss on top end

[i'mabassfishingfool24_7]

my 40 hp yamaha,3 cyl. which is on my flats boat starts,idles,does everything you wish until you try to run "full throttle". at that point the miss starts slowly and continues to get worse. to the point to where the miss doesn't kill the motor but you must back off. when i back off the throttle to approx. 3/4 throttle the miss disappears and the motor runs smooth again.<br />i've changed fuel connectors, fuel tank,fuel pump,fuel primer ball,spark plugs,drained carb bowls,shot carb cleaner into carbs,and into drain holes.. now i'm lost???

 

[jim dozier]

Re: bad miss on top end

You were probably on the right track when you were looking at the carbs but you did an incomplete job. Take the carbs off and dismantle them, and do a thorough cleaning/rebuild. Clean ALL of the orifices and jets, use carb cleaner AND compressed air, install the rebuild parts, check the float heights, and reset the idle mixture screws.