Merc 470 - again...

J

jazzbrother

Recruit
Joined
Jul 4, 2004
Messages
3
Here goes;<br /><br />I own a '79 Silverline with a Merc 470. I have had it for about ten years. I love the size of the boat (16 1/2 ft - closed bow) and the power of the motor - when it works.<br /><br />I have two chronic problems. The first is that the battery is inevitably dead after leaving it sit overnight. Presumably this is some sort of slow discharge that I haven't figured out. Don't know how to find the problem, but I guess it's a wiring issue of some sort. It must be a slow discharge because it's okay if I just leave it for a few minutes or an hour or two.<br /><br />The second, more fundamental problem is that after running it at cruising speed for more than ten minutes or so the motor will just decide to cut out. It simply goes dead while running at full speed. After it does this, I typically cannot get it started for some length of time - usually ten to fifteen minutes or so. <br /><br />When it does start it's almost like a switch has been flipped - it starts fine and runs okay until I get past half throttle or so at which point it will then cut out completely again.<br /><br />When it does this I'm convinced it has lost its spark completely as it is very sudden.<br /><br />Could this be related to the dreaded alternator problem this engine is known for? Or is it more likely something else?<br /><br />Could the two problems be related? (It's always been really hard on batteries.)<br /><br />I don't know much about engines but am willing to get my hands dirty. The local marina has been pretty much useless on this.<br /><br /><br />I have vowed several times to ditch the boat and replace it with something newer, but;<br />1. It's only worth $3K or so(?)<br />2. I'd have to pay five to ten times that for essentially the same thing in a newer, reliable boat.<br />3. My boathouse ain't that big. There aren't many 16 1/2 ft boats with the power this thing has available in a newer boat. <br /><br /><br />Any thoughts would be appreciated.<br /><br />Thanks!
 
S

sroger007

Cadet
Joined
Jul 5, 2004
Messages
20
Re: Merc 470 - again...

My money is on the coil or the distributor cap. They get warm they fault
 
N

Northern Eclipse

Senior Chief Petty Officer
Joined
Jun 24, 2003
Messages
665
Re: Merc 470 - again...

My fathers Wellcraft with a 3.7 was doing the same thing, this is what I found last thursday, <br /> Motor would start and run good after running it at 3000 or more rpm for 10-15minutes motor would start to misfire and then quit, check for spark at coil got spark, remove plug lead from distributor cap no spark, remove cap check for spark at points, rotor have spark, put cap back on ,no spark ???? remove cap again then notice that the black wire going to the points has been crimped with a butt connector and was being pinched by the distributor cap, thus wore a bare spot and was grounding out on the distributer housing. taped it up and motor started right away, and put 6 running hours on it without another failer, I have now ordered a new wire and the rubber groment that was missing for wire to pass through the dist. housing, instead of being pinched under that cap. Another point to check is engine temp, if its running hot or has a poor water flow from impeller the voltage reg will get to hot and cause a shutdown, the regulators are water cooled on the 470, heat will cause a voltage resistance, also the big 4's need a big strong battery and good battery cables, My Pops 3.7 would eat batteries, I changed the cables to 10 guage and put a 900 cranking amp series 27 battery, hav'nt fried one since.
 
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