14 replies to this topic

[Hammer42]

Anyone have any idea why when I take off my HT leads the terminals on the ignition coil arc towards the king lead?

New dizzy cap and spark plugs have been put on.

Edited by Hammer42, 06 November 2016 - 10:01 AM.

[Ethel]

HT is the plugs leads, not entirely sure under what conditions you mean it sparks. A spark is generated when coil's field collapses, by design when the points (or electronic do dah) breaks LT the circuit.

[Hammer42]

When the engine is running I'm pulling the 3/4 plug leads trying to diagnose why they are not firing. While doing this I noticed when I take one of them off there is arcing on the ignition coil between the terminals and the plug for the lead that goes to the dizzy. I only noticed because I did it in the dark.

[sledgehammer]

The spark will be taking the shortest / lowest resistance route to earth

 

wipe the coil nose clean & make sure LT terminals are bent away from coil nose & cond good

 

- it will probably still happen , sounds like you have a healthy spark , 

 

this indicates your cap is good as it isn't arcing inside , it has to jump the next closest source to earth

 

if you do this a lot it will start breaking down the insulation on the coil nose

 

are the plugs getting wet & is there compression on the affected cylinders ?

Edited by sledgehammer, 06 November 2016 - 11:02 AM.

[Hammer42]

Plugs had soot on them I leaned the carb out a bit checked again now 1/4 are white and 2/3 are still black. Compression checked, all at 160psi. For some reason it just doesn't seem like it's sparking enough inside 3/4 to get ignition (I'm only running on 2 cylinders, 3 intermittently).

[rusty789]

Sounds similar to what my coil was doing and that was cracked.

[sledgehammer]

if they are new leads - check them anyway 

 

I've had a few faulty ones from new

 

swap them around see if the fault follows the lead

 

& as above check coil nose for damage

Edited by sledgehammer, 06 November 2016 - 11:04 AM.

[Hammer42]

Ah sorry should've mentioned I've done all the swapping over trying to get it to follow however it is isolated to 3/4.

Here is my coil, can't see the arcing though due to flash. It does look like some plastic has chipped away from the terminals could this cause the arcing?

[Spider]

Sounds like the plugs that are 'sooted' are in fact fouled.

 

When they are like that, they are effectively shorted out and won't spark.

 

New plugs are usually needed though sometimes they can be cleaned.

 

It happens most often from a rich mixture.

Edited by Moke Spider, 06 November 2016 - 11:18 AM.

[sledgehammer]

I would change that coil

 

nice crack there

[Hammer42]

The sooting that was previously on 1/4 has been cleaned off by the engine after I adjusted the mixture however are now white. 2/3 are still fouled though, not as bad.

[Hammer42]

That's what I'm thinking I just don't want to be changing parts just for the sake of it. Just trying to get to the root cause of why it's running on two cylinder's with apparent spark to all plugs, new dizzy cap, and valve clearance set carb also seems to be working fine. So I'm just a loss really. I will change the coil as I don't think those chips are helping the cause regardless.

[sledgehammer]

wonder if excess fuel in cyl is fowling the plugs ?

 

whip all the plugs out , turn it over with coil disconnected , & rag draped over the head to stop fuel spraying everywhere

 

to try to remove any excess fuel / oil

 

dry everything off , start again

 

how is the air filter ?

[Hammer42]

Air filter is new K & N type. I will give the cleaning a go in the morning and see how it goes. Hopefully i can get a coil here fairly quickly, what would you recommend for a balasted lasted type? It looks like I have the pink and white wire although faded so I'm assuming thats ballasted also says resistive or something of that nature.

Edited by Hammer42, 06 November 2016 - 12:22 PM.

[tiger99]

The reasons for the arcing have been well explained above. However why not try to clean and dry the coil thoroughly around the HT terminal and its extended insulator, put the lead back in and spray it with a good coating of Damp Start or whatever they call it now, the stuff that leaves a clear insulating film. The chipped insulation around the LT terminal is largely irrelevant.

 

As for the plugs, why not clean them as best you can, and swap them so the bad plugs are in the good cylinders, maybe just one at first, then both. If the engine starts, running for a while should either foul up the bad plugs, if they are the cause of the problem, or burn the crud off them and foul up what were the good ones if it is an engine (carburettor, manifold, valves, pistons etc) fault. Please don't spend money on replacements until you have tried all that.