Tinware sparks when attempting to start engine?

Hi, a good friend and I are trying to get to the bottom of a poor running and very difficult starting 1971 T2 crossover. By accident, we discovered quite significant sparks jumping from the tin ware across to the flexi hose pipe on the air filter. This is/was a little disconcerting and coincided with the van completely refusing to start. Any help or advice would be greatly appreciated.

 

Check all the ht leads to see if any have split or rubbed through anywhere

 

Check your HT leads, king lead, coil and dissy cap. Likely you have a lead with knackered insulation somewhere.

 

Also worth checking the choke wire isn’t shorting

 

As @Dubs said above - I’d suspect the HT leads. Even if the insulation looks ok I’ve seen them break down under load and spark in random places along their length.

Stirlingmoz

 

Hi, thanks for the advice, will be back on it next week, so will report then.

 

Hi, thanks for all of the advice. My friend and I tried to start it last night so that we could see where the sparks might be coming from. Just typical that the stupid thing started almost straight away and ticked over reasonably ok for 10 minutes before we switched it off. During this time their were no sparks visible anywhere. We left it for 15 minutes and then couldn't get it started again. I am at a loss about what could be causing this.

 

I've moved this thread to mech an tech for you where it will get more attention for your subject

 

Maybe the engine cupboard is wet with condensation. We have had a lot of rain and cold damp days lately. Condensation forms everywhere even inside the distributor cap. WD40 and a wipe down will help displace the moisture. Mine wouldn't start last week for that reason.

 

Loose ground wire on gearbox left hand side near front of gearbox.
The fat sparks are likely 12 volt power jumping from the tinware bolted to the engine over to the air cleaner clamped and grounded to the body work.
Measure the resistance between the engine block and the chassis. Should be a solid zero ohms.
Or measure the voltage when you turn the key between tinware and body work and it doesnt start. I bet its 12 volts. If it is then look at the earth strap...

 

If that strap is missing, at least on a Bug, the ungrounded static from the gearbox will travel thru the accelerator cable and can, in some circumstances, burn out the cable itself.

 

^what Mike said. I reckon your gearbox/engine earth strap has fallen off. The fat sparks are the starter current trying to find another path to the engine.

 

I think they reason it didn’t restart is a leaky float cutoff valve. If the engine starts fine from cold but never very well when warm I bet this is the problem. A friend of mine had exactly the same issue. Change the valve and then all good.

 

Or, as on my old automatic Ford, weld the kickdown cable open, meaning I had to drive everywhere in first gear...

 

Agree with checking the earth cable however 12v won’t jump the gap unless its a very small gap, not enough voltage. Also due to the current consumption of the starter motor a break in the earth path would stop the starter turning.
More likely a HT spark

 

The starter current on my 1641 is only 50 amps... even 2.5mm2 wire will take that for a bit..

One day when you are bored take a well charged old car battery and a breaker bar and short the terminals, the sparks of molten metal, and the arcs will be impressive if you dont just weld the bar to the tags...
Just remember that your MIG welder only uses 16 to 22 volts to create a really fat metal arc.
The technique of using 2 car batteries in series with a flux coated welding electrode is also a well known field welding trick when the suspension of your Toyota Landcruiser breaks in the jungle en route to the end of the rally stage..

What will happen is that the thin metal touches at a single small point which provides a low resistance but thin path. This takes the current and burns out making a flash of molten metal plasma. Vibration causes another bit of metal to contact and so on.
Just like a MIG welder with wire feed set too fast.

It may also be the strap is just loose in which case it takes some of the current through the proper path..

 

Totally agree Mike, i have inadvertently shorted out many car batteries in my time.
I was meaning unlike a HT spark which will jump a fair size air gap a 12v battery supply won’t. If it’s a high resistance point touching like the tip of a welding rod you can produce sparking/arcing. As you say the concept of mig welding