burning out spark boxes - why?

1988 /1989 25hp Merc Model 1-025211g<br /><br />Over the last 4-5 years I have had replaced about the same number of "spark boxes". I dont use the boat that much and it took a while to see what was actually taking place. Something is "frying" the spark box after about 15-20 hours of use. Then motor only runs on one cylinder. What could be the underlying problem that is ruining the spark box(s). The boat mechanic says he is using factory replacement parts. <br /><br />Thank you for your help,<br />Forrest

Re: burning out spark boxes - why?

If you are only getting spark on one cylinder once it fails, I'd suspect a weak coil, and that might eventually cause the box to go bad. Especially if it is always the same cylinder that quits. Just guessing here, but if you haven't replaced the coils and coil wires, that would be worth a try before you buy any more CDI boxes. Bad grounds are worth checking also. <br /><br />Perhaps others here can offer more informed opinions.

Re: burning out spark boxes - why?

If the engine is electric start the ign switch or wiring could be putting 12v to the box and killing it

Re: burning out spark boxes - why?

Originally posted by Forrestr:<br /> 1988 /1989 25hp Merc Model 1-025211g<br /><br />Over the last 4-5 years I have had replaced about the same number of "spark boxes". I dont use the boat that much and it took a while to see what was actually taking place. Something is "frying" the spark box after about 15-20 hours of use. Then motor only runs on one cylinder. What could be the underlying problem that is ruining the spark box(s). The boat mechanic says he is using factory replacement parts. <br /><br />Thank you for your help,<br />Forrest

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Re: burning out spark boxes - why?

Thanks for the info. I will check out coils and wires prior to replacing CDI box. This motor does not have electric start.<br />Forrestr

Re: burning out spark boxes - why?

Forrestr--please let us know what you find out.<br /><br />And if Laddies or any of the other true experts here have a take on this please jump in! My experience is limited to my own motors which are a bit older, and the electrical systems do change.<br /><br />If it is firing on just one cylinder now, you could try swapping coils. You should be able to do this by swapping both the plug wires and the wires from the CDI box to the coils, without physically removing the coils themselves. Then see if the problem moves to the other cylinder or not. If the problem is then in the other cylinder, then that would indicate a bad coil. If the problem stays with the same cylinder, then it is either the plug wire or the CDI box. The latter (problem in same cylinder) still doesn't tell you what is causing it, but the former could narrow it down if the coil proves to be bad. <br /><br />Make sure to draw and label things before moving them around. A digital camera is really useful.

Re: burning out spark boxes - why?

There's nothing else wrong with it. Those boxes pop about every 1 to 3 years. It's a 2 cylinder thing that's been around since they started using that box.

Re: burning out spark boxes - why?

4-5 CDI boxes in 4-5 years doesn't sound normal to me. Unless it is a known fault with the specific box used on that particular motor. If that is the case, perhaps a Rapair brand replacement CDI instead of Merc would be worth a try. Or unless the motor gets a lot of hours on it every year, like a rental or commercially used motor. The fact that one cylinder goes instead of losing spark altogether also seems suspicious, particularly if they always fail the same way and it's always the same cylinder that goes out.

Re: burning out spark boxes - why?

verify all wiring and all connections are good and clean. problems occur when a ground wire has failed, etc.

Re: burning out spark boxes - why?

I am taking it to the shop tommorow (Fri- 23trd), I am printing out all the info I received from this post to give the tech. Thanks again for the help. I myself do not know if it has always failed on the same cylinder or not ( it always run the same after failing). If it comes down to it normally burning out after 1 to 3 years -- I am getting rid of the motor. But the hours of usage is so low (15-20 hrs) it seems like it has to be something else causing it to fail. I will let you know what they found- hopefully something!<br />Forrestr

Re: burning out spark boxes - why?

Check the grounding of the secondary winding on the ignition coil, and all other grounds. If you coild have the "pigtail" ground on the secondary winding, make sure it makes good contact where the coil is mounted. Coil will have to be removed to see this, IF if is the kind with the pigtail.