M/C 470 Several Questions

[a1nowell]

M/C 470 Serial #6684523:

1) When I bought this boat in '08 it had already been converted to Petronix ignition, my coil went out last April, I replaced it with a universal 12 volt coil from NAPA. Should I be using some sort of Petronix coil?

2) Do you set the timing with a dwell meter? If so what are the specs since I have the Petronix ignition?

3) I have the alternator conversion kit from breezeworks, here latley my guage only show about 13 volts or less. I sense a problem, do you?

Thanks,

Larry

 

[DaveG55]

Re: M/C 470 Several Questions

1- Don't know anything about the coil you bought from NAPA. But I do know that the better the coil the hotter the spark, the hotter the spark the more through the burn.
2- No, you don't set timing with a dwell meter. You set point dwell with a dwell meter. Since you no longer have points you no longer use a dwell meter - unless it is also a tach, then you might still need it for idle speed, tuning the carb, etc. What you need is a timing light. You adjust timing by turning the distributer in the block while watching the timing marks on the flywheel. Sorry, I don't know off-hand what that engine should be set at. Maybe 8 deg BTDC but that's just a number floating around in the dim room that is my memory.
3- What were you getting before? 13 volts is a bit low but it's still charging the battery. Why do you suspect the alternator? It could as easily be the voltage regulator starting to fail.

 

[lselmes]

Re: M/C 470 Several Questions

Mercruiser bulletin for the 470 changed it to 4 deg BTDC from 10 deg BTDC because of modern fuel issues. Most guys run at 6 deg BTDC with the Pertronix Ignition/ Flamethrower coil combo. Double check the Mercruiser bulletin's for your serial number as it may have been for just the earliest models. I know it included my 1981 470.

 

[generator12]

Re: M/C 470 Several Questions

a1, if it runs well with the coil you bought, it's likely to stay that way IF the coil is made for the full 12 volts, and doesn't require a resistor. (Info on this came with the Pertronix.) If the coil doesn't run hot, you're probably alright.

As Dave said, you need a timing light if you're going to set that. I second the 6 degrees BTC - that's where my 470 is set and it runs well.

As to the 13 volt reading, it could easily be a gauge error - a voltmeter reading slightly low. Happens all the time. All you need is about 13.5 volts when running to keep the battery up just fine. Much higher tends to "boil" the electrolyte a little - makes you add water a bit more often. I would double-check it with an accurate meter. If you're at least 13.5V, you should be good.