Sparkplug issue

[Goro F]

hello
i m having problems with spark plugs on my R51/2

When I took the bike for the first time Bosch W5AC were mounted. Then the one on the left cylinder, when i was running suddenly failed

I discovered that the original sparkplugs use for my bike were Bosch W240T1 / W4AC

So I bought a couple of NGK B8HS, which I understood are the equivalents to the overmentioned Bosch

Yesterday evening again, one cylinder suddenly failed. I assume that the sparkplug on that cylinder doesn t work properly anymore. Now i left the bike in a garage of my friend, as soon as i can i will go to check if the problem is the sparkplug again

I think no more than 200 km run so far with the new NGK sparkplugs and for 2 times i had issues with the one mounted on the left. What are the possible causes and what i must check?

- carburetion? even if the engine runs smooth i noticed that it s rich, maybe richer on the left. Some oil infiltration in the left cylinder can cause the breakage of sparkplug?
- gap of sparkplug? i never checked
- sparkplug heat range? i choose the equivalent to the original bosch but maybe it's not the right one for the actual condition of my engine?

thx for helping also on this problem

[schrader7032]

Can you take good closeup pictures of the two spark plugs so we can see what they look like?

[Goro F]

Here we go, the left and the right

Left just replaced this morning with a new one. I confirm that the problem yesterday was the sparkplug of the left cylinder. This picture is how it appears after a ride of 20 km more or less.

[Goro F]

and this is the left which is not working anymore… carbonized I would say..

[schrader7032]

The last picture does seem to show it all. I'd say that is oil fouled.

[Goro F]

Piston rings worn out i assume… am I wrong?

Is there any way to contain and survive untill i do the replacement?

[schrader7032]

Have done a compression test? What about a leak-down test? They would give you some clues as to where the problem was. But if you can't drive 100 miles without fouling a plug, that's going to get expensive!!

You could experiment with hotter plugs...I think they tend to burn some of that stuff off.

[skyler.robbins]

I’d make sure your valves are adjusted to spec.. and your carb isn’t too rich for the mix.
Also.. I agree with an earlier comment on compression test.

[Goro F]

It seems difficult here where i live find good workshop for vintage BMW. I tried with a couple of workshop without success. The bike is having a lot of issues the i tried to fix step by step

I never did personally the compression test, the leak down test neither. I will look for the devices to check both.

On the side of the broken sparkplug , the airmix screw of the carburator is visible much more out than the other, nevertheless it does not seems to make the sparkplug more clean

I checked the valves gap and set both at the upper limit spec (0.15 mm intake, 0,2mm output).

[808Airhead]

Make sure your slide needle is in correct position. If you have correct carburetor then mixture screw out is rich. Plug fouling is too much oil or fuel….