A few questions before I start to tackle the rough idle.... I've been poking around the forum and got some good leads on where to start but had some lingering questions. My 120 runs very smooth on high end but idles very rough and continues up to @ 2400 rpm before it evens out (rough erratic idle, some popping/coughing and surging). Carbs were thoroughly cleaned and floats set (held bodies upside down and set the floats to set even with body, I read somewhere about how they should be hanging a little down, I can re-set them if people think it's worth it). Compression is all around 150 and within a few pounds (only 15 hours on top end rebuild). I made a spark tester for an ignition problem (turned out to be keyswitch) and set the posts to 7/16". When cranking motor the two top cylinders had consistent spark but the lower two seemed to be intermittent. That's where I'm starting today, cleaning/checking all the leads/contacts and swapping coils to see if the problem follows. The questions I have are, if a coil was weak would it produce an even spark at higher speeds vs. an idle? Also, I have an inline tester (lights up with spark)for small engines/autos that is not adjustable, should I be able to see a strong spark with that style of tester installed? My lawnmower produces a stronger spark than the boat according to the tester. The spark across the homemade tester @ 7/16" seem like a pretty good arc to me but not large blue flash, more like skinny lightening. If that doesn't sound right, where would be the best place to start testing? I also found the CDI troubleshooting guide and was wondering if my regular digital multimeter can be used without the DAV adapter for those tests.
Also, on a side note... setting the idle speed. The manual I have shows diagrams of the idle adjustment screw, which doesn't quite look like my motor. By their description, I would be turning the long, fluted black plastic knob with the spring loaded rod coming out of it, but on the carb box cover, that seems to be labled as the spark dwell adjustment (and I was told not to touch that by a mechanic friend that unfortunately is not around anymore). Could anyone clear this up for me. The idle is @ 600 in the water, not too low but it seems like it could be higher.
Thanks again for all your help! This forum has been invaluable!
Evan
Also, on a side note... setting the idle speed. The manual I have shows diagrams of the idle adjustment screw, which doesn't quite look like my motor. By their description, I would be turning the long, fluted black plastic knob with the spring loaded rod coming out of it, but on the carb box cover, that seems to be labled as the spark dwell adjustment (and I was told not to touch that by a mechanic friend that unfortunately is not around anymore). Could anyone clear this up for me. The idle is @ 600 in the water, not too low but it seems like it could be higher.
Thanks again for all your help! This forum has been invaluable!
Evan
