Listen to what kghost and Bondo are saying! And please do not put thru-hull exaust on a 470! It will sound like cheet and I guarantee you will get water into the engine sooner or later especially #4. Also, check your exaust flapper in the exaust pipe to see if it is intact. Some guy from Texas tried the same thing with the thru-hull exaust deal and posted the outcome that I just described. He blew the engine up and was upset because it had run perfectly until that point. I asked the same questions on a few sites not so long ago. I have the same identical engine package on my boat. If you plan on keeping it, do the pertronix ignition upgrade and keep the old points on board in case something takes a crap. Did the previous owner do the aftermarket alternator kit or do you have the imfamous water cooled voltage regulator and the rectifier at crank (generator) setup? If so that is good!, If not you could have problems with overcharging or undercharging of electrical system. (boiled batteries or dead batteries not to mention performance problems such as possible weak spark situation causing hard starts, rough idle, backfire or worse. The alternator setup costs around $300-$400, The pertronix setup should cost you around $85-$95 if you can do it yourself. Believe it or not, you might cause an argument on another site trying to support these two critical upgrades by some old timers who swear by points and the original voltage regulator setup. I don't agree because the second I installed the pertronix setup I was able to attain a lower idle and overall the motor just seemed to have more power than with the points. Get a 40,000 volt coil for it as well, but don't go to high (alot of heat for a small little cap). Have the front seals on the water circulator pump ever been changed? What"s the compression like? Has the engine ever had an overheat? One last thing, If it is not there, install an overheat buzzer light and even an overheat shutdown (something to kill power to the coil or ignition so as not to blow head gasket) Overheating a 470 is bad news and can cause you alot of grief so do whatever possible to avoid it. jmho
Whether I like it or not at this point I am married to this engine system! lol ( I spent alot of money on rebuilding engine, I did all work except machine work myself and it still cost about $3600.00) Parts are getting hard to find for this particular engine system and they are not cheap! I like the economy that the engine gives but if I were to do it again, I would have gone with a carbed 4.3 litre v-6 or even a small block v-8. Don't expect too much from this motor in performance and enjoy the thing as long as you can. best of luck, Tom