General Category > Quadrajet Carb Talk and Tips

4MV Marine swap

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LouC:
I believe this is correct, the most commonly used one is the GM EST system, used by Volvo Penta and others. Merc has their own system Thunderbolt IV and V. I am still running an ancient Prestolite points distributor with full mechanical advance. Works just fine actually.

Cliff Ruggles:
Points are preferred for Marine use simply because if/when they take a crap (which isn't often) you can have it back up and running in a few minutes.

I recommend installing a set of points into the distributor for each engine, set the dwell, then remove them, seal in zip lock bag with new condensors and put them in the boats storage box in the console.

Install another new set of points/condenser, set the dwell, ignition timing, and sleep better at night.

If/when they take a dump you'll be back up in minutes, and don't forget a good fitting screwdriver on board in your tool kit or put one in the bag with the spare points.  If you have the type of distributor where you have to completely remove the screws than hold down the points/condenser grab a few extras and put them in the back with the spare parts.  Most of those screws will be #8 or #10 and either 24 or 32 pitch.  You can get a hole bag of them for a couple bucks at most fastener stores.

I'm not fond of electronic conversion kits, even for automotive use.  You will NEVER break down in front of Summit or Jegs and require a flat bed back to the house.  Contrary to what companies selling "bug zapping" distributors will tell you, there isn't a single ounce of power waiting for you by converting them.  You may get a little quicker cold starts with MSD stuff, and slightly improved idle quality IF your carb is a little lean at idle, but from idle to the shift point they make the same power as anything else provided the timing curves are exactly the same.

With a boat you can get stranded miles from the dock and become a SAR case, or even get injured or killed if a storm comes up or you get ran over by a barge.

I was a Coast Guard boarding officer for several decades.  As far as inspections and carriage requirements we typically only look at the flame arrestor to make sure it's still in place, and a working ventilation fan for enclosed engine compartments on small craft as far as the engine bay is concerned.  So you woln't get a violation for converting your points distributor to electronic or replacing it with something aftermarket, but as mentioned it's not a good idea......Cliff

LouC:
Agreed I have no problem with points and do keep spares, and a feeler gauge on board with the small screwdriver needed to change if I have to. In my case the boat has an OMC Cobra drive system which uses an Electronic Shift Assist module that lowers the idle speed to allow the clutch dog in the lower unit to release. This is what allows you to shift to neutral with a load on the prop.  This module only works with points, it will not work with the electronic system unless you use a diode fix (might not be reliable in a marine environment) or a properly set up new Assist Module made to work with electronic ignitions (CDI electronics in Alabama makes such a unit). The Mercruiser system actually momentarily shorts out the ignition on the dog clutch Alpha drive and if the shift cable is a bit sticky it will stall the engine. The OMC system is more sophisticated in that it lowers the rpm from about 600 to 450 and will not stall the engine, if its in good enough tune to run at that speed.

I wish they had made a marine version of the old Delco window style points distributor. The easiest ever to set the points on. I still have that flex allen wrench tool from the 70s! Worked great on Chevrolets, Oldsmobiles and Pontiacs  with the distributor all the way in the back.

Cliff Ruggles:
I wish they had made a marine version of the old Delco window style points distributor. The easiest ever to set the points on.

Those distributors were excellent and still a good many around.  They don't need much help aside from driving the roll pin off the gear and removing the shaft to clean the mechanical advance mechanism up.
 
I also zinc plate all the metal parts to keep them from rusting and replace the thin rubber sleeve on the advance pin with a stainless steel one.  To convert to Marine us you can eliminate the vacuum advance and just bolt the plate down, then make a cover for the side of the housing to keep water and debris out of it.

NAPA still sells the good points/condenser "uni-sets" so you can switch them out in seconds and don't have to worry about dropping the screw holding down the condenser into the bilge!......Cliff

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