When I disappear from the forum for a while, almost always something happens. It's like every week there is a new problem. 😭  I've dealt with fuel delivery problems again and more electrical issues... But now, new theme is: Energy Crisis. Prices have gone crazy. The gap between gasoline and LPG is so narrow now, it's the same or only a little difference between using any of them. Considering my aged LPG system, using gasoline for a while would be a better choice. I've completely overhauled the carburetor a couple of months ago so I sprayed some carb. cleaner inside of the carburetor, removed the LPG mixer which is restrictive for airflow. I've screwed the airbox with its original retaining ring.

Two days ago when returning to home, uphill acceleration, the car suddenly lost power and started to rock back and forth. I released the gas pedal and pulled over. Idle speed was reduced like a quarter or more. Exhaust was smelling unburned fuel. There was apparently an ignition issue. I suspected about the distributor. After opening the distributor cap, there was oil inside of the cap walls.(Maintenance oil spray with centrifugal force) I cleaned it thoroughly. I started the engine again but there was no difference.

 

When the engine was still running, I decided to unplug spark plug leads one at a time. (Even wearing rubber coated work gloves, and holding from insulated end fitting, I got shocked! It's a bad idea to hold the chassis with your other hand when pulling spark plugs.) I started from forth. When I remove one lead, the idle rev reduced more. Finally when I tried the first, it did not have any effect. That means cylinder no1 wasn't firing. I removed the spark plug to see what happened. The plug's side electrode was looking like if there was a layer over it, and that layer was cracked and disintegrated. One of the tiny pieces was between the electrodes, shorting the spark plug. It was night with other people in the car so that was a quick fix with no pics. sorry. İnsulator core was covered with light brown/grey dust but I saw a small notch at one side. I gave the spark plug a quick cleaning with a sand paper piece and the power loss issue was gone.

 

Like many parts of the car, the spark plugs may be old. Maybe ancient. I must change them. I could hardly read the markings but the current ones are Champion RC12YC. (Are they already wrong?)

 

From now, everything gets messy.

Before opening this this topic I've read a lot about spark plugs and their indisputable importance about power, fuel saving and engine health. I've read other user's experiences about spark plugs. It's very very critical to choose right plug.

Advised plugs for Favorit 135 engine (carb): Champion C9YCC. For higher compression 136 engine: Champion S7YCC. (Both are not available anymore)

I've got the head skimmed before when repairing head gasket failure. I don't know how much they skimmed it (I don't know if this was the first skim the head ever got too) but it's sure the compression is higher.

My ignition system is not standard. The distributor and ignition coil are from Renault 12.

Distributor: Magneti Marelli S148A.

Ignition Coil: Magneti Marelli BE200B Mk1.

I'm currently trying to make a perfect tune for gasoline but there is a possibility to use LPG later.

 

How can I choose the right spark plug now?

 

Narrowing the choices got me into these:

Bosch FR8DC/FR8DC+ (for 135 engine)

Bosch FR6DC/FR6DC+ (for 136 engine)

 

Should I go for colder FR6DC? Or direct substitute FR8DC?

 

I can also choose from Magneti Marelli, Brisk, NGK.

Edited 22 October, 20214 yr by R_Blue

I also run bosch plugs with lpg will update with the model later, just gap them to 0.7mm for lpg or 0.8mm for gas and you are good to go for 15.000km easily

1st

2nd

3rd

4th

 

Broad daylight shows that the first spark plug is looking damaged.

Insulator core is chipped. Side electrode seems cracked?

 

5 hours ago, Thefeliciahacker said:

I also run bosch plugs with lpg will update with the model later, just gap them to 0.7mm for lpg or 0.8mm for gas and you are good to go for 15.000km easily

Thanks for the info.

 

I've found a set of Russian made Bosch FR6DC+ 's. Price was near the half of market average. I'll give them a go and see what happens.

Yes I am running FR6DC+ gapped at 0.7mm but what half price are you talking about I mean they cost 2euros each

I can also tell you that your engine was - is running hot aka you need colder plugs.

Edited 23 October, 20214 yr by Thefeliciahacker

15 hours ago, Thefeliciahacker said:

Yes I am running FR6DC+ gapped at 0.7mm but what half price are you talking about I mean they cost 2euros each

I can also tell you that your engine was - is running hot aka you need colder plugs.

So I made the right choice buying FR6DC+ instead of FR8DC. Thanks! That is a relief.

About the price...well.

Sometimes 2=3 or 2=4.  When you see 2=2 that's a green light.

First 100KM impression with LPG from new plugs: (stock 8mm gap)

 

-Engine is less affected from electrical loads from other sources. That was a real problem for me. I have a dedicated thread for that issue you know. There was electrical issues with the main cables from alternator that I've repaired. Now the rev. drop is all time minimum.

 

-I'm expecting better fuel economy.

 

Should I reduce the gap to 0.7mm? I've read that Kettering arc distributors' ignition coils are weaker than electronic ignition distributors' coils.

6 hours ago, R_Blue said:

gap to 0.7mm

yes lpg - air mixture has greater dielectric strength that gas-air

@R_Blue

Go with original NGK spark plugs and you'll be fine.