View Full Version : 87 prostar - engine dies after idle
06-25-2013, 10:28 AM
Hey Guys -
Been having some issues with the boat. Boat will run fine if you start it up and pull people skiing. The issues are when you idle around for a little bit, or keep trying to get somebody up skiing. An extended time of low idle causes the engine to essentially sputter and die. You can usually get it started, but the minute you put it in gear it will shut off. Or if you can manage to get it in gear and get moving, throttling up makes it sputter and not get up to speed. If you let sit for a period of time after this, usually it will run fine and you can take off. Again, we can ski on it fine, but its after idling around for a bit the problem comes.
We were having the problem last year, and had the carb rebuilt over the winter. We have the Holly 4160, and the boat is a 87 prostar with the 351w and powerslot. Rebuilding of the carb did not fix the problem, and I am not sure what to do next. Not sure if there are adjustments on the carb that could help? Any ideas would be appreciated.
06-25-2013, 10:44 AM
Could be as simple as your idle speed is a little too low. What RPM are you idling at in gear warmed up? I actually don't pay to much attention to the actual RPM on my boat. I just keep it as slow as I can get away with but 600-650 is a good number.
Next to look at are the basics.
Do you still have points or have you converted to electronic ignition? Points need to be adjusted frequently by setting the dwell (and adjusting timing accordingly). Point gap isn't close enough if you want a perfect running engine. Also verify the timing is correct. Electronic ignition makes a huge difference in starting and running and worth the upgrade if you haven't already.
Spark plugs, distributor cap and rotor should be changed at least every two years at a minimum. Carbon build-up will cause minor running issues.
Spark plug wires should be changed every five or six years. They can last longer, but again, if you want a perfect running engine it's worth a few bucks and a little time.
Fuel filters should be changed annually.
You might also check down the throat of your carb when it doesn't want to restart to see if any fuel is leaking out causing it to flood.
06-25-2013, 10:51 AM
thatsmrmastercraft nailed it.
Also, when your engine dies touch the coil. Is it hot? Is it scalding hot? A poor ground increases resistance and can overheat the coil.
Run the boat at idle at night -- do you see any sparks jumping? Your wires may be old and tired.
06-25-2013, 11:09 AM
Not sure what the number is that it idles at, but never seemed to be too high or low. I'll try to take a look this evening to see what the number is.
Ignition is electronic. Converted it over a couple years ago. Spark plugs and wires were changed out the beginning of the season. Cap and rotor are a couple years older...so I'll look into changing those.
Filters were also changed to start the year. Any possibility it could be a fuel pump issue? Or does the fuel pump usually cause issues at higher speed?
I'll also try to take a look at the coil and wires and see if I can find anything.
06-25-2013, 11:11 AM
New wires? How'd you route them? Please see my latest post here: http://www.mastercraft.com/teamtalk/showthread.php?t=55442
06-25-2013, 11:17 AM
Fuel pump is almost always a higher speed issue.
You can always take a flat bladed screwdriver and scrape off any carbon deposits on a cap and rotor. If you see immediate improvement you know you found your issue.
Coil ground is always a good thing to verify. Good on catamount for bringing that one up.
You might also consider your idle mixture. If you are running too rich, it will show up as an issue when you are fully warmed up.
Also, have you verified that your choke is opening fully after the initial 90 seconds?
06-25-2013, 11:22 AM
One more thing to check for is corrosion at spark plug and coil wire ends. A little high resistance can cause some small problems. While you are doing this, apply a little dielectric grease to the ends before re-installing them. It will help fight off any future corrosion.
06-25-2013, 11:37 AM
Interesting on the wires Catamount. I don't think that is my issue, but I will check it over. The boat has no problem when pulling people at speed. Four of us can ski one after another with no issue. The problem comes when we put/idle across the cove. Seems the boat can handle idle in small doses, but when its for a pro-longed period of time is when the issues come.
I'll look into a quick clean of the cap and rotor and see if anything changes with that.
Idle mixture is something that seems a more likely issue to me. Thinking back, I would say it usually always happens when the boat is up to temp. We will fire it up before we start, and the boat will idle while we get ready to go with no issues. It usually comes after we pull our first set.
Also going to look at the coil ground. Last Sunday the boat died, we tried to get it moving again with no luck. It would start, but couldn't get it to go into gear without dying. Let it sit for a little. After that, we tried to fire and it wouldn't do anything. It was as if it had no spark....which makes the coil ground something to look at.
Did check the choke and it does open fully.
06-25-2013, 11:42 AM
A failing kill switch will give a person all sorts of headaches. They often do intermittent things before failing completely. You might bypass that temporarily until you get this worked out to eliminate it as a possibility.
06-25-2013, 12:10 PM
Well you will know if it's flooding at idle by cranking over at WOT. That will blow out the excess fuel and introduce air.
One quick thing to try is to make sure the idle air bleeds are clean. These provide the air at idle speeds. Even the smallest spec of junk can clog these guys up and make you run rich at idle.
The idle air bleeds are the outermost bleeds on both the primary and secondary throats.
Put a straw on your carb cleaner and blast through these to make sure they are clear.
07-29-2013, 10:01 AM
Just wanted to give a quick update on the issues. After going through everything, and talking to everybody we could think of, it seems our issues is actually the coil. The coil seems to overheat, and is throwing out all kinds of problems which is resulting in the boat running poorly after we have skied a few runs. Once it gets real hot, we can cool it with a cold wet rag and it will run fine again. Thanks to catamount for putting us on to this.
The coil is only a couple years old and seems to have failed. Does anybody have the correct wiring diagram for the coil with a ballast resistor? I'm thinking we have something wired wrong, and is causing the coil to overheat and fail. We ordered a new one from Skidim, but don't want to install it with the old wiring if its wrong and have the same issue.
Also, I talked to Mallory and they suggested using one of their coils without a resistor. Anybody have experience going this route. This is the coil suggested