Motor Sputters after a bit

[BoatFromHell]

Hay guys:

New to the forum here. Got a mind stumper of an issue going on here with my dads boat. Let me give you guys some specifics on the boat first before I get into the issue I got going on here.

Year of boat: 1988 or 89
Cobalt CS Series 220
7.4L Bravo Engine
Inboard

Issue that I got going on here now. The motor starts to sputter, bogging down and surging. Thing is at first the boat runs like a champ from a cold start. Meaning it has not been used in a couple of days. We take it out tool around a bit, turn it off and come back to it a 1/2 hour later and start it up and take it out again but now it starts to sputter and what not as soon as we get it up to about 30 mph. Its like it does not want to go. I am afraid that it will die on me with me out in the middle of the water. And I do not want to row back to the dock.

We have had the carb rebuilt, the fuel pump added, gas tank cleaned out, new fuel separator, updated the points and condenser. After all of this we thought we had fixed the problem, but it still gives us issues after a bit of use. Any thoughts or ideas on what could be causing this issue would be nice. Cause, I am all out of ideas on why this keeps happening. And would love to use the boat with out any fears that I am going to need to bust out the oars to get back to the dock.

thanks.

[AsLan7]

.
Hey BfH. Welcome to the Cobaltchat forum. So glad you found us!

Sorry to hear about your boat engine woes.

As you know it’s either gas/air or spark (sometimes both but rare). You didn’t mention plug & wire replacement. Were these checked?

Any pics?

Again welcome aboard mate.

.

[BoatFromHell]

We have replaced the following:

1. Plugs and wires
2. Fuel Pump and filter
3. rebuilt the carb
4. cleaned the fuel tank
5. replaced the water separator

like I mentioned it runs fine when it is cold and has set over night for about an hour, hour and a half then it starts to sputter and bog down and then it takes off like it got a shot of fuel. Very...very very strange. I thank you for welcoming me and my dad to the board and hopefully we can get this fixed so that it is a fun boat from hell not a non fun one.

shawn

[akorcovelos]

How did the old plugs look when you changed them? That will tell you a lot. When you cleaned the tank did you replace the feed line with the check valve going to the fuel pump?

[jhnmdahl]

Fuel lines are a good place to look, but it sounds a bit like vapor lock (especially given the recent weather around here). Does it make a difference if you leave the engine hatch open? Or maybe pour some cool water on the fuel pump if it's an external and see if that does it. Sure sounds like something's starving fuel, and you've done a good job of replacing the most likely candidates already.

[Big Block Power]

Fuel lines are a good place to look, but it sounds a bit like vapor lock (especially given the recent weather around here). Does it make a difference if you leave the engine hatch open? Or maybe pour some cool water on the fuel pump if it's an external and see if that does it. Sure sounds like something's starving fuel, and you've done a good job of replacing the most likely candidates already.

I'm with John on this. Also sounds like it's running lean. Just because the carb was rebuilt doesn't mean it's working correctly. When it's cold it's running rich. Extra fuel runs good. Warm runs bad starving for fuel runs bad. Do a fuel pressure test with both conditions. Do a fuel volume test during both conditions. Also how is the vent. Leave the fuel cap loose. Also when coming to a stop before you shut off the engine let it idle for a few minutes to let cool gas fill the float bowl and cool it down.

[BoatFromHell]

We replaced the coil today and that seemed to do the trick, after everything we did it boiled down to that. Do not know why the coil would cause such an issue but it did. So, now you can let the next person that runs into this type of problem know of this fix as well. Now it is a true boatfromhell...zips around foxlake like a dream....40 mph with out a hitch..yea !!!

[jhnmdahl]

BFH, thanks for reporting back on the fix - hopefully it will help someone else who is having a holiday weekend in jeopardy sometime get up and running. Enjoy your 4th!

John

[Big Block Power]

Very good. Cool controls your spark. So it sounds like you weren't getting enough of a spark in your life. Glad you got it.

[AsLan7]

We replaced the coil today and that seemed to do the trick, after everything we did it boiled down to that. Do not know why the coil would cause such an issue but it did. So, now you can let the next person that runs into this type of problem know of this fix as well. Now it is a true boatfromhell...zips around foxlake like a dream....40 mph with out a hitch..yea !!!

.
So it was spark. For some reason I had a feeling it was this side of the equation. Nice fix and thanks for reporting back for others to diagnose.

Still waiting for pics.
.

[BoatFromHell]

No problem...all I know is that I had fun with the boat yesterday...jumping the waves from some of the bigger boats on the lake...oh what fun...

[akorcovelos]

Love a quick fix for the holiday! We’ll be heading to Blarney Thursday for the races again, you going to go? I’ll shoot you an email tomorrow.