I used a hand vacuum test pump to check the needle seat for leaking ~ try that plus remove the float and give it a shake IF it has fluid inside replace it ~ the 1987 Mikuni OEM float should be an exact replacement ~ your engine might be flooding ~ a vacuum pump test is valuable for checking all the diaphragms on your truck including the vacuum advance on the distributor & the 2nd dary butterfly actuator on the carb & vacuum lines too ~ wishing you a quick fix George