i have a 75hp mercury 4 stroke carb engine, i have a poping noise at idle, i was wondering if the engine timing could be advanced causing noise, i have even compression on all cyl 150psi, good spark on all cyl, used timing light and all cyl even flash of light no misses, it runs great at all rpm range just pops at idle, i can remove one of the 4 carb syncro plugs in the intake, doesnt matter which one and noise goes away, can put my finger over the hole lightly and it will bacfire (pop) and burn the tip of my finger and a flame comes out, i installed a vac gauge on each syncro plug one at a time at idle the gauge flucuates from 0-25 inhg on each cyl dont know if this is normal, just sounds like the timing is to far advanced. I haven't checked yet but was wondering if the temp sensor could cause the problem, say disconnect the sensor at idle and see if the noise changed, havn't done it yet. I pulled all the carbs and rebuilt, soaked each one in carb cleaner with no luck, the factory plugs over the carb adj still in place, ran seafoam in tank still no luck at wits end with this please help, i want to sync the carbs but dont have any gravity sticks dont know if this would help, even done a cyl leak test and 10% loss well within spec, please let me know your thoughts thanks
