Sparkplug issue

[Goro F]

yes I agree, changing the heat range do not solve the issue. It's important identify and address the root cause of the fouling.

In the next days I hope to have some time to observe as vechoriv1373 suggested and make the other test (I should receive soon the tester for the cylinder compression, still looking for somebody here having the leak-down device)

NGK B7H instead of B9H, you 're right. I did a mistake. Hotter spark plugs transfer heat slowly, tips remain hot longer and consequently burn off carbon deposi, so I must go from 8 to 7, not to 9.

I understood from niall4473 that NGK is not anyhow the best . Any better alternative?

[Goro F]

anyhow i try to explain me the physics why, as mentioned in the bing manual, if I turned out the mix screw (20) a weaker mix is obtained, if I turn it in a richer mixture is obtained. Since this screw is in the fuel path above the idle jet, if I screw it out I should make the fuel passage bigger then a richer mixture. Where I go wrong?

[schrader7032]

This particular adjusting screw actually has a hole running through the middle of it. Air gets into the screw coming under and around the small cap that is on the outside. The air then goes through some small holes near the outside and then through holes that are in the tapered end of the screw. When the screw is turned in, the flow of air is reduced through the screw, thus making it richer. When the screw is turned out, the flow of air is easy to get into the carb, thus making the mixture leaner.

[Goro F]

thanks, 100% clear now. So I also need to be sure that the air passage on this screw are absolutely free and clean, otherwise it could make the carburation rich anyhow.

hope also that i don't have a "Frankenstein" carburettor. I see some sections which show the same screw with o without air passages.

[808Airhead]

I think it may be your air filter “foam”. Try to source an original filter element or even try without the element to see if it improves. Everything else being OK, the filter foam can be quite restrictive.

[wa1nca]

Wouldn't both plugs be fouled if the air filter
Was restricted not only left side ?

[Goro F]

Compression test done right now at cold. Right cylinder is a little bit higher but for the variability of the measurement its self i would say comparable.

What shall be the compression level?

[metoo]

Your compression is low. should be around 120-130 psi.

[808Airhead]

Make sure you are holding throttle wide open when doing your compression test. If you are, then that is low. Maybe a ball hone and new rings gapped correctly will remedy this , otherwise it may be bad valve sealing . Either way, that compression is low. If fouling plugs, more than likely rings or extremely worn guides.

[Goro F]

Yes when I did the test i did it with fuel closed and the throttle fully opened.

I check the carburators just to be sure, fuel paths and air paths. Nothing strange found. I riassemby them and set the mix screws as per spec ( 1 and 1/2 out from the fully in point)

Later i will do again the carburation following Duane method. Just kick the engine and it starts immediatenly. After couple of min i notice that the right head is getting warm faster then the left.