Off Topic Mercruiser problem

Ross17

Ross17

Well-Known Member
I have a 1988 4.3 litre Mercruiser with Thunderbolt ignition. I am having a problem when the engine heats up, it will begin to misfire and quit. It acts like it is running out of fuel. You let it cool off for 15 minutes, and it will start and run fine. Engine temperature doesn't go over 170, and it runs fine if you leave the dog house off. Any suggestions?
 
I have heard there is akin available to convert to electronic ignition. Would you know where I could get more information on them?
 
Does it have a flame arrestor?
could be plugged up a bit?
my old OMC was doing something similar to what you’re describing.
cleaned out the flame arrestor real well problem solved..
 
I agree with dunnster...replace the coil...they are relatively cheap. Back in the day, if I kept $1 for every time I had to diagnose those symptoms and it almost always turned out to be coil, I could afford to have 2 X-wives...just say'n.
 
I have a 3 Litre Mercruizer and I took my choke coil right off. It is at the front of your carb with the two wires going to it. Turn your ignition on just before you back the boat into the water. By the time you jump into your boat your choke coil would have been heated up and your choke would be fully open. When you start your boat, it will start up right away without any black smoke coming out your rear end. Derek9 is also right. Take out your flame arrestor and sonicate or wash in very hot soapy water then blow out with compressed air. Starting up with a closed choke creates the black sooty plugged flame arrestor.
 
I had a 4.3 in the early 90’s. It was a great motor (basically a 350 with the back 2 cylinders “sawed off). Always ran great until I replaced the choke “heater coil” unit that opens the choke plate. The choke would not open. With the help of a friend I found a gasket between the new choke unit and the motor block (kept the electric choke coil from completing a circuit to ground to allow the coil to open the choke plate). Threw the gasket away and the motor ran fine.
 
Before electronic ignition came into the picture, we always carried a book of matches (for gapping), allen key and a point file with us. Provided a quick fix when the points decided to act up. I do believe however, what Ross17 is describing is a classic symptom of a coil failure due to over heating (internal). Could be something else though I would first change out the coil...cheap fix.
 
I am going to try a coil. I had the choke issue 2 years ago. The choke is still operating fine. Thank you for everyone's input. This site really is a wealth of information.
 
I would suggest that you are getting a vapor lock with the fuel. This happened to me in a car, it would only happen when I was towing. I removed the insulation from the hood, and all was fine after that. It was something to do with the fuel getting too warm. Just a thought, maybe vent the doghouse.
 
Thanks reel, I was thinking that as well but it doesn't seem to get that hot under the dog house
 
Got a price from NAPA for a coil, they have to order it out of Winipeg. I'm going down to see Dave at Stans to see if they have one
 
You can also try CarQuest, APC and even Hully Gully as far as that goes. Don't buy in a used coil especially one that has been sitting on a shelf at a marina as it can also be defective from a previous swap out. You can't tell by looking at them.
 
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