Merc 470 Missing and dying after about 30-60 min

[cshirley]

I have a 1978 Wellcraft AirSlot with a Mercruiser 470 (170hp). I know they aren't the best engines but I'd like to make it work for now until I can afford something better. I took it out last summer and it would run pretty well for about 30-60 min before it began missing out. It would start off here and there and then within about 5-10 min it would barely stay running and die. Temperature seemed to be fine although its possible that the gauge was wrong I guess.

I'm about to begin working on this problem again, so if you have any suggestions, I'd appreciate them. I bought a Pertronix Ignitor to replace the points ignition but haven't been able to get it on because I think they sent me the version for the pertronix dist instead of the AC Delco that I have. I figured this would help.

Would a had gasket be causing this?

Thanks,

Curtis

 

[a70eliminator]

Re: Merc 470 Missing and dying after about 30-60 min

Check compression then get back with us, anything else is just quesswork.

 

[searay3]

Re: Merc 470 Missing and dying after about 30-60 min

A couple of things come to mind. typical of a failing coil. runs for a while, gets hot, stops working. Also a plugged vent, but 30 minutes is a long time for that. If you can duplicate on the trailer, or even out on the water for that matter, pull the main coil lead, hold it or lay it near the block, crank it and see if you still have spark. I am assuming a full tune up was done....

 

[180shabah]

Re: Merc 470 Missing and dying after about 30-60 min

Check out the adults only sticky

won't reach WOT and testing fuel system will cover just about everything.

 

[Don S]

Re: Merc 470 Missing and dying after about 30-60 min

It could be nothing more that a plugged up fuel vent for the gas tank. After 30 minutes it could be building up enough vacuum from the fuel pump that the pump can't suck fuel from the tank and the engine dies. If you let it set a few minutes, the vacuum ceases a little and it will run again till the level of vac gets to much again. Let it set overnight and you are back to the 30 to 45 minute mark.
Either do the fuel system tests in the Adults only sticky (recommended), or run it till it stops again and take the gas cap off and see if the problem goes away.

 

[bhammer]

Re: Merc 470 Missing and dying after about 30-60 min

The guys are correct... Check out the sticky. I had that engine as well. It was a great engine but had its few trouble areas. Well taken care of, it will perform.

I had a very similar issue and found that my coil was bad. I also had a fair amount of junk in the gas tank. If it is the coil, take the time and do the upgrade to electronic from the points.

 

[CAPTKEV85]

Re: Merc 470 Missing and dying after about 30-60 min

I upgraded to electrionic on my 470 what a difference. starts on a half a turn.

 

[cshirley]

Re: Merc 470 Missing and dying after about 30-60 min

Some really great suggestions guys. Thanks for the info. I don't have a compression tester with me but I know I need to get one. The coil looks ancient and the paint has peeled away from it. I was thinking about picking up a Pertronix Flamethrower 40000 volt coil for it as they seem to be around the same price as what I'm seeing for the stock and may improve run-time. Also, I talked to Pertronix and they say maybe I wasn't pushing the magnet down on the dist shaft hard enough so this may be my problem in which case I'll have the electronic ignition installed soon.

I think I checked the fuel vent last year when I was having problems and it was ok but I will check again this year.

I haven't been able to duplicate it on the trailer but I haven't run it wide open for 30-60 min on the trailer. And you guys are right, once I get it trailer'd and it sits overnight it fires right back up the next day.

I'm looking to do the alternator conversion and I'm wondering is everyone actually paying $250+ for a few metal brackets? I'd rather try and fabricate my own based on pictures with that kind of money.

Thanks,

Curtis

 

[bhammer]

Re: Merc 470 Missing and dying after about 30-60 min

Yup, the pertronix is what I did as well. Made a big improvement. The hardest part of the whole job was to file out the area on the distributer cab for the wires to run.

If your magneto style charging system is working, then I would forgo the alternator kit. I always kept a battery start box with me so if the alt failed, I had a backup. If you watch your gages, you will see that it has failed and can head for shore. You can find drawings on the net to make your own brackets. It is pretty simple. I think that price also would include the 63 amp MARINE alternator.

Have you had to do the speedy sleeve fix for the camshaft yet? If not, it'll be worth while to make sure the hole on the bottom of the timing cover is not clogged or blocked. Here is a pretty good 470 group: http://www.breezeworks.net/cgi-bin/MBoard/forum/display_forum_topics.asp?ForumID=1