Rough idle?
 

502 magmpi mefi 1. Idle seems rough and surges quite a bit on a cold start.Had fuel injectors cleaned and tested, so had plenum off, also had to disassemble distributor due to heavy corrosion on magnets. Put back together fired right up. Seems like when I set the timing to 8° just doesn't want to idle for crap. Other than the idle, seems too run great. Put it in service mode, bumped idle to 1600~1800 as I set it to 8° it seemed to almost want to stall...had to keep adjusting throttle to keep it from stalling. Should I advance timing a little more make it idle smooth, or will that hurt the motor? Stock motor with msd ign box and gill exhuast.Plus previous owner had ecm re flashed for better performance...any thoughts?

More timing the motor will idle better. Just check timing above 4000 full advance. Should have 34-36 full advance, idle around 24

Do you know if it was set at 8* before you took it apart???
If the ECM was reflashed it could have been done with the intent of more base timing and less advance built in.
It is also risky to just start bumping the timing up without knowing the specs on the timing curve in the ECM.
It could be advancing all the way through 5000rpms or more. It should be fine to bump it 10* but I wouldn't do more unless you have the ECM specs.

Thanks guys...should checked the timing before but it wasn't firing because of distributor was so bad. But marked it before taking it out.Think my paperwork said Arizona speed did the re flash.Try to dig up the paperwork when I got the boat, then try to call them. Gonna try to bump it to 10 and see if improves the idle then pull plugs and check..it seemed like it was way advanced on first fire at 1800 rpms...had to turn distributor a bit to get to 8.

MEFI 1 timing tables stop at 3200 rpm. Unless the F1 slope extension is some crazy number the advance essentially stops at 3200. I agree with everything else. He's gotta find what base timing is set in the ECM and then match it on the distributor when setting base timing.

Found the prevous owners paperwork on the ecm flash. Precision Marine did the ecm handwritten notes look like its set at 36*-38* @ 1500 rpm and 32 * total at 3100rpm and above.Doesnt mention anything about base timing???