Technical 1969 FIAT 500 'Spitfire' F

[SDHXIII]

Hello everyone.

After a bit of advice and opinion please.

I have a 1969 500 F with a 126 650cc engine. I have had it for a while now and it has never really run that well. The long and short of it is I have tried many things over the years including have a Powerspark ignition system installed.

Despite this it still isn't great. When running it seems to pop intermittently. I have recently added silicone HT leads as recommended on this forum as the garage that installed the Powerspark system put the old leads back on. I have also replaced the spark plugs.

Tonight when I started the thing up it was still poppy and lumpy and I noticed that it was sparking or firing at the base of the carb as it popped. I have put a video on YouTubes and you can clearly see the sparking



The question is; what could causing such a thing and what could a remedy be. I'm a bit worried, given the location of the sparking that the whole thing could go up in flames

HELP!!!!!!

Thank you.
Stuart....

 

[Bounding Bambino]

Thats a ghost in the machine if ive ever seen one. How in the world does a spark even occur there. Maybe its the shutter frequency so we dont see the spark jumping from the HT boot? Everything around those plug leads is ground, so im confused how a spark "from the looks of it" is jumping from the throttle butterfly lever to the valve cover. The carb is grounded ( at most thru the mounting bolts, and at minimum the choke cable).

First thing i would suggest is a new set of leads and boots. Obviously they are not containing the fury within those cables lol.

Only other place i could think is, the cables are sparking to the valve cover inside/between where the support bracket and cable gland is above the exhaust manifold. If used with all the right gaskets, technically, the valve cover is isolated from the engine ground. Cork gasket on bottom, and gaskets under the washers for the cover, no metal on metal contact that i could think of. Cable sparks to the cover, then valve cover is sparking to the carb.

Take a look at the cable in that area and see if the bracket has worn thru the black gland, and into the silicone cover.

Its all a long shot. But i would look at a new set of leads. even though those are recently new are they a good brand?. Something is going on here.

 

[Goldnrust]

It certainly is an interesting problem! Good idea above to check if any of the cables have worn through on their metal guides.

Also have you checked your engine ground strap? If you have a poor engine ground then the spark could be jumping as it's trying to find its way to something thats grounded properly.

 

[the hobbler]

It certainly is an interesting problem! Good idea above to check if any of the cables have worn through on their metal guides.

Also have you checked your engine ground strap? If you have a poor engine ground then the spark could be jumping as it's trying to find its way to something thats grounded properly.

I agree with both 'Bounding Bambino' and 'Goldenrust' as to what to check---and yes, if you have electronic ignition you DO need to use silicon ignition leads, and NOT copper leads. Like them, I have never seen this before!

 

[myoshik]

Years ago, a mechanic once showed me how he would check for faults in the spark plug wires. He would take an insulated screw driver, attach it to earth, and slowly drag it along the spark plug wire. If the wire was faulty, we would see a small spark jumping from the wire to the screw driver. I recall the spark we saw wasn't nearly as strong and could only see it at night.

Sorry I know that doesn't help much...but as already mentioned above, guessing it's a problem with the leads?

 

[SDHXIII]

Update

Well after plenty of Googling without much success, I decided to take a look myself. On closer inspection at the point that there was a spark appearing at the base of the carb. There looked to be a bit of a gap, so removed the carb and drip tray on the basis that either or might be warped.

Carb was fine so just gave it a good clean up, however there was a slight warp on the spacer/drip tray which I remedied with a flat surface and a sheet of 120 grit.

New gaskets all round and hey presto, we are running better than ever. I'm guessing with a bit of air getting in, I over compensated the fuel making everything a bit rich and extra combustion. Play the videos one after the other they really are chalk and cheese.



On to the next job... Spongy brakes.

Stuart.

 

[dangfiat]

Looking good! That's what did it for me as well. Replaced all the gaskets and cleaned the carb, that cured most of my spitting issues.

Still cold blooded on start. Have to wait a minute or so before I can get going (or it will bog on throttle). But after warm up it's all good