Running rough with new carburetor and old distributor

[512Cobalt]

Hey there,

I'm looking for some troubleshooting guidance on my 1994 Cobalt 220 with the 5.7L.

It has a fresh motor and many other new parts. Also still some original equipment in there that could be 25 yrs old, such as the points distributor.

Ran great all day 2 weeks ago, then the next weekend wouldn't start. Turns out the mechanical fuel pump was toast, so I installed an electric one and it fired back up. While installing the electric fuel pump I also installed a brand new Holley Marine carburetor in place of the old Edelbrock. Took it our for a spin and it ran beautifully for a few minutes and then seemed to start misfiring so I brought it back to the dock. Then it had a hard time restarting and when it did there was a loud whistling noise while the engine was running so I cut it off. Also, my Cobalt ignition key cylinder switch (replaced last summer) started intermittently staying in 'start' mode when I backed it off after cranking. It did sit outside in the rain all winter with the key in the ignition. Additionally, the ignition coil was extremely hot to the touch.

I'd like to rewire the ignition coil (source and grounds) and check out the key cylinder switch (maybe install a push button start switch). Can anyone help me find the ignition circuit wiring diagrams?

Eventually, maybe immediately, I plan to change over to the MSD marine distributor (not the 'Ready-to-Run' model, as I heard it was junk) with the 6ML-2 ignition control box. Either way I need to become more familiar with the wiring of this motor first and verify things are correct after having the motor replaced.

What are the red and black button by the bulkhead on the Exhaust manifold riser? I noticed the red button has a thick red wire coming from behind it which is constant +12V.

Any advice or wiring resources will be appreciated!

[akorcovelos]

The red button is the mater breaker, it's fails so your boat doesn't burn to the waterline. You're kind of all over in your list of issues, lets break it down more clearly.

How did you install the electric pump? Return line? New FPR? Did you try putting the old carb back on?

The whining noise could be the pump churning if you have no return and it's deadheaded.

That distributor won't have points, it's got an ignition module that can fail after time, pull the cap and look, if it's rusty replace it. I've heard horror stories about pretty much all the MSD stuff on boats, which is why you can get them used for dirt cheap places like OSO. People troubleshoot them for months only to ditch them and go back to stock and have no problems.

Are you sure the key is what is sticking and not the starter?

My advice, get it working with the stock parts before just throwing upgrades to try and fix a problem you have't even fully diagnosed yet. Who rebuilt and installed the engine? Have you talk to them about any of this?

[512Cobalt]

Great questions. Thank you for the reply!

I used the Carter universal marine pump. It's supplying 5.5psi with no return or regulator. The whistling was only when engine was spinning, and because I had the wrong size tee for the oil pressure switch the fuel pump temporarily runs when the engine isn't but there is no abnormal noise in that situation.

I think I will try putting the old carb back on since it ran great that way before the fuel pump went out.

The guy who replaced the motor had me pickup the points from the boat dealership when he had to replace them last summer. He also mentioned something about them or a wire to them shorting out in the distributor and having to use tape or something to "fix" it. I don't know what this means, but it doesn't sound good.

I too have had issues with some MSD products before, but when they are functioning properly they're nice, hahaha. Is there another ignition brand with better reputation for marine applications that I could use to replace the 25yr old points setup?

It might make more sense that the starter solenoid is sticking, rather than the key switch, didn't think of that!

[akorcovelos]

My '84 had the electronic ignition module, I'm very surprised yours has points. Doesn't yours have the Thunderbolt ignition? Post a pic of the inside of the dist, might help identify the problem. Typically when electronics like the coil get hot it's a grounding issue somewhere.

[nolaboater99]

Be sure you are using a marine electric fuel pump rather than an automotive pump and as was said you need a return line to keep from blowing up you and your boat.
Shawn