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90 hp merc fouling plugs

J

Jerry Glenn

New member
I have disconnected my oil tank on my 96 Mercury and am mixing the gas with oil manually at 50:1 and have a problem with rough idle and teh plugs fouling. I realize at idle the mixture should be less concentrated and the oiler compensates for that when installed, but I do not have confidence in the auto oiler due to previous bad experience. I have the idle jets set as the manual states at 1 and 1/4 turns out. Is there a different setting I can make to keep the plugs from fouling out. I have manually tried to adjust them at idle but do not really notice a difference in idle speed. Can I adjust the timing from 8 degree BTDC to improve idle?
I appreciate any ones help! Thanks

Jerry
 
Plug " fouling " is due to low heat in the cylinder / weak spark and not the fault of the plug !------------Start with a compression test, report the results if you like.-----------Test and see if spark will jump a gap of 7/16" on all 3 leads.--------Is the thermostat installed and working properly ?
 
racerone said:
Plug " fouling " is due to low heat in the cylinder / weak spark and not the fault of the plug !------------Start with a compression test, report the results if you like.-----------Test and see if spark will jump a gap of 7/16" on all 3 leads.--------Is the thermostat installed and working properly ?
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The power head was rebuilt at the end of last season. Compression good on all three cylinders at 120. Spark is good, jumps more than a half inch. I recently replaced the coil packs with CDI coil packs. The thermostat works although I haven't measured the temp of the head, I will next time out. The motor runs fine all day long, just idles like crap and when I pull the plugs after idle they are covered in oil. If i idle long enough, one of the cylinders will not fire well and it takes a long time to get on plane. If i change the plugs out it immediatlyl operates normally. I am just curios if there is a way around the rough idle or I guess I will hook the auto oiler back up.
 
I have manually tried to adjust them at idle but do not really notice a difference in idle speed.
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If the carbs are working properly you should be able to notice the difference when adjusting the idle mixture so the idle is not rough. Did you rebuild the carbs as part of the rebuild? Perhaps it is time for it. Adjust the mixture VERY S-L-O-W-L-Y and you'll notice the slight differences. I add a 1/4 CCW turn to the screw when it is idling smooth to richen it slightly...it won't run well if it is too lean and it may cause damage the pistons.
 
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