Something strange going on with my new 650cc (500 conversion) engine. It runs like a top until it gets real hot. Then when I hit higher RPMs before I shift it, the engine starts to buck and I can feel the engine losing power. See video of how it’s idling when I pulled over. If I stop it, it’s very hard to start if it even will. Today I tried something. When I got home and tried to restart it, I couldn’t. Then I pointed an electric leaf blower at the coil for a few minutes and it started right up. Coil is new, points (gapped properly), condenser new, spark plug wires new. Thinking I should wrap heat tape around the coil. Any other ideas?


https://youtu.be/YE7QamGUtIE

I had a bad spark plug. When hot (post 10 - 15 mins drive) it started to short. Once cooler, could start the engine etc. Have you checked the plugs? Got a meter on the coil, spark leads and plugs.


R

lazylobster said:

I had a bad spark plug. When hot (post 10 - 15 mins drive) it started to short. Once cooler, could start the engine etc. Have you checked the plugs? Got a meter on the coil, spark leads and plugs.


R

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I didn't check the plugs but I will. I think I may install a heat blanket around the coil as well.
Also I have the upgraded muffler on it that has thicker pipes coming off the head and doesn't allow the factory heat shield to be put back in place.

So it seems the new coil I purchased might have an issue when real hot. I swapped it our for an old coil I had that was a bit wider in diameter. It is quite old and covered with engine/road gunk but it cleaned up nicely. The make is KLITZ. I also fashioned a heat shield from the OEM heat shield that I can't use anymore due to the upgraded exhaust. This seemed to have solved the problem. I took it out for a spirited drive and didn't have any issues with engine bucking at higher rpm. Keeping fingers crossed.

I have posted before about this but check your leads and especially the plug extenders with a meter for resistance. If there is to much it makes the coil work harder to overcome this and it overheats and fails. Try it without the plug extenders to see if it cures it. I don't know why these cars are so critical about this ,maybe just because of the tight engine bay and being air cooled .I have a few other cars of this age and never seen this on them.

phoenix1 said:

I have posted before about this but check your leads and especially the plug extenders with a meter for resistance. If there is to much it makes the coil work harder to overcome this and it overheats and fails. Try it without the plug extenders to see if it cures it. I don't know why these cars are so critical about this ,maybe just because of the tight engine bay and being air cooled .I have a few other cars of this age and never seen this on them.

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I'm sorry. Not sure what you mean by plug extenders.

Because we are talking about heat, is there a maximum length the lead from the coil to the distributor can be? While we are at it is there a maximum length of wire for the condenser to the coil?

Joe R

The plug extenders are two plastic connectors between the plug and the plug lead. They fit on the plug with the rubber grommet around them . They are intended to keep the plug lead out of the heat created round the engine. I am sure without them your leads will probably last a good while anyway. Best look on one of the parts suppliers website to have a look at them. Bryan

This is a plug extender,


https://www.ricambio.co.uk/spark-plug-extension-classic-fiat-500-126

Fiona500f said:

This is a plug extender,





https://www.ricambio.co.uk/spark-plug-extension-classic-fiat-500-126

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Ah! Ok. I don’t have plug extenders on my plugs. Just straight leads right to the plugs. They are new plug wires.

I don't have plug extenders either and my baby runs great. Seems some do, some don't.


I do have silicone leads. Brought the best I could find.
R

126 engines are not fitted with plug extenders

Toshi 975 said:

126 engines are not fitted with plug extenders

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That's interesting. If anyone will know that it's you!!! I can't disagree with it, (much as you know I would love to ), but the Haynes manual does refer to "separate interference suppressor plug caps which are screwed onto the spark plugs"; could that be the real intention and purpose behind them when they are fitted?

Well I am going by my own personal experiences I have never come across a 126 engine with those extenders fitted and that includes the very original 594cc from the earliest known 126 in the UK.
However the factory workshop manual for the 126 does show them in the large cross section drawing of the engine. It is possible that if they were ever fitted they would have been removed if unsuppressed copper ht leads were replaced with the modern silicon ones. I have also never seen the extenders advertised for 126 engines.
I have sometimes found that the text for the Haynes 126 manuals is taken direct from the 500 manual without being updated with developments.