Ignition problem

[deverett]

My hit n miss engine has developed an ignition fault. The spark is very weak almost to the point of being invisible, so preventing the engine from running.

The engine uses a standard Kettering type ignition with points and coil. The battery pack (9.6 volt rechargable) is fully charged. I have tried using a 12 volt battery with no difference in sparking ability. The points are clean. The plug is brand new, although it makes no difference whether I use the old or new plug.

So over to you panel of experts for a possible cure, please.

Dave
The Emerald Isle

 

[nobeard]

In my days working garages the kettering ignition system with a weak spark was usually down to a degraded condensor or a few short turns in the ignition coil you mentioned the points coil and battery pack but no mention of the condensor.

 

[deverett]

Thanks, nobeard. I'll change the condenser and see what happens.

Dave
The Emerald Isle

 

[jasonh]

I've been able to damage a coil by leaving the points in the "make" position for too long. With no ballast resistor excessive current causes the coil to get fried. There was no visible damage, but it didn't work anymore. I added a ballast resistor and was more careful about the position of the crank. You can tell if it's fried by measuring the primary and secondary resistance for correct resistance.

Regards,

Jason H.

 

[Paulsv]

I've been able to damage a coil by leaving the points in the "make" position for too long.

I did this while charging the battery on my 1961 Triumph TR3. The coil actually exploded, showering the garage with melted tar, and there were billows of smoke coming out of the garage. Unfortunately, it happenned in the middle of a dinner with my in-laws. Wow, did I feel stupid.

 

[Lawijt]

I read 9.6V. Then are you working with a Nicad or a Nihm battery cells. They can not so good peaking.
You have to take a 3s LiPo battery. They can peak @ very high amps. Also do you have than 11.1V very stabilised.

Barry

 

[deverett]

Thanks gents for the other replies.

Thinking about it, if I am getting some sort of spark, it would suggest that the coil is 'working', although perhaps not at 100%. My understanding of the basic ignition system is that the condenser acts as a spark amplifier, so this is what I will replace first. Condensers are cheaper than coils!

Next question: is any condenser for a 12v system OK, or should I be looking for a specific type?

Dave
The Emerald Isle

 

[nobeard]

condensors on kettering systems seem to vary from 1uf to 2 uf but are high voltage otherwise back emf from coil will destroy them ,these are now getting harder to obtain with this system now never being used on vehicles.last time i needed one i had to go to a maplins store and buy a 2uf at 400volt but NONE ELECTROLITIC they just come with two wires any one of the 2 wires ground to earth the other to the points works well if you cant get the proper steel cased ones.

 

[deverett]

Thanks nobeard. There are quite a few ignition condensers for sale on that well-known internet auction site, so I will go for one of those.

Dave
The Emerald Isle