Wow – 2 posts in one day – that must be a record or something.

One of my jobs this weekend was to get my Atomic Bomb (Atomic 4 Gasoline Marine Engine) running properly. When we moved the boat from our winter slip over to our summer slip, I noticed that I could not get the engine over about 1200 rpm. It should hit 4000 easily. Of course, I left that problem until I really needed the engine – like this weekend when we wanted to go sailing. Here is what I found.

The engine idled well – or I should say it seemed to idle well. But when I put the boat into gear and revved her up, the engine would begin to bog down and would not go above 1200 rpm. So…

I made a couple of assumptions: I doubted that the prop was fouled as we have not been out anywhere where it could have picked something up. I also assumed the gasoline was OK as it would run in a seemingly normal fashion at idle – certainly not rough anyway. So I decided to check to see if it was my electrical/ignition system. With the engine running I removed each spark plug wire one by one and determined that this here A Bomb was only running on 2 cylinders. Removing wires 1 and 4 made no difference to how the engine was running but removing 2 or 3 would almost stall the engine. So now I had narrowed it down to 1 and 4 – but what was actually happening with them?

Next I pulled the wire off of 4 and positioned it close to the engine block and turned the engine over. The spark jumped strong and hard from the wire end to the engine block. I did the same thing with wire number 1 with the same result – there was good strong spark.

So, now I knew that at least the ignition system was good to the plug – the final thing to check was the plugs themselves. What I did was pull out plug number 4 and connect it to the wire – then placed it on the block so that the plug body was grounded and then turned the engine over – ah ha – no spark. Tried the same with number 1 and again no spark. So what we have is spark coming to the plug but no spark at the plug.

Fred Hawood, the original owner was kind enough to leave a set of used plugs in my engine bin. They were nicely wrapped in a baggie and tagged ‘Used 1998.’ So I eagerly ripped into the bag and replaced plugs 1 and 4 with these ‘used’ plugs and …. tada – we have a full power engine again. This Bomb had 2 bad spark plugs! I can only guess that the insides must have corroded over the winter – but that is just a guess.

Does anyone know how spark plugs fail? I don’t mean burn up, I mean fail – not spark anymore. They appear to be fine – not cracked – no carbon trails, just not firing. Anywho, if the weather holds out, we are off sailing tomorrow.

I hope you enjoyed this another episode of Marine Engine fun – by far the biggest headache I have with this boat: my Atomic Bomb.

"Atomic 4 Problems…" by was published on July 2nd, 2007 and is listed in Atomic 4.

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Comments on "Atomic 4 Problems…": 1 Comment

  1. Anonymous wrote,

    For the cost of plugs, who cares what went wrong? just buy 4 new ones, and you should be good for another 9 years.

    But, since you asked… A few common, but not too noticeable things can cause plugs to fail: Cracked Ceramic Insulator (somewhere in the body of the plug), Gap too wide, Carbon Fouling.

    Least likely: You mention that you can’t see any carbon between the cathode, and annode, but it is possible to have a carbon trail down the insulator on the plug. To test, take an Exacto knife, and scrape the insulator all the way around the center electrode.

    More Likely: get an Ohm meter (if I remember correctly, you are a technical kind of guy, so you have one) and test from the terminal on the top of the plug to the center electrode. This should be low (<20) Ohms. It is likely that there is (was?) a resistor in the plug, and it may have smoked giving you infinite Ohms.

    Less Likely: if this still seems OK, check from the terminal to the grounded body of the plug. This should be infinite Ohms. If you are getting something less, then there is a short somwhere in the plug.

    A good picture of a Plug can be found here:

    Best of luck, and keep the blog going!


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