Sparkplug issue

[Seek]

The idle mixture screw regulates the air. Out is more air, thus a leaner mixture, in is rich.

But that really looks like oil. So either valve guides, piston rings or a damaged head gasket.

[Goro F]

I ' ve R51/2 bike with Bing Carburators 1/22/61-62 which were originally mounted on R51/3. On my bike were used /39-40

I refurbished them as per spec of Bing, following the data sheet set up of the carburator types (main differences between the two types of carb were the main jets, 105 vs 90). Clip position on the needle is in the first groove for both and is here where i placed

turning adjusting screw in is producing richer mixture, out leaner. I send a couple of picture where is visible that i m running really with the air screw out on the left carb and this seems not having influence on sparkplug which remains fouled. This could confirm that the probelm should be oil and not gasoline.

[Goro F]

Here the pictures of carb

[cbclemmens]

It could be something stupid like the choke staying on, or putting its self on while riding. The fouled plug look like it is way too rich. Is it oily? Or just carbon? Just carbon suggests too much fuel too little air. An oil fouled plug would likely be oily to the touch.
BTW Higher numbers on plugs usually indicate a higher heat range so your W5 plugs are probably a heat range higher than the W4s. One way to deal with older engines that burn a little oil is to go a heat range higher with the plugs.

Craig

[Slash2rider]

You didn't write a word about bike behaviour, how the engine pulls,does it work as it should at all throttle openings,vibration,smoke if any,wet pistons,dry pistons.Don't expect much change to spark colour from idle circuit settings unless you ride at tickover revs.If it's a fuel problem do you have right set of needle jet and jet needle fitted?

[808Airhead]

I just looked at my carb body and I was incorrect, even on the older carbs turning mixture screw out DOES lean the carb out at idle….SO…. Your left carb has screw out much more than right side. Do a compression test, and are you 100% sure your timing is spot on? Retarded timing will make it idle weird as well. Also #1 position on slide needle is top groove, is that the position you are using.

[Goro F]

i share more info

the engine is running good apparently, also to ears more expert than mine. Start at the first kick, idle stable, running smooth from low to higher rpm. No hesitation at full throttle. At cold start i notice little bit smoking from the left muffler, where i have the problem of fouled plug, but immediately disappear when the engine is getting warm.

on the carb:
slide needle is set at the first groove from the top
idle jet and main jet new. Idle jet 40, main jet 105 as per spec
floating needle and float are new
i did not change the idle mix screw needle and slide needle since they looks in good condition.
every passage of carb is free and clean (i used ultrasonic + brushes to make it clean)


air filter:
the original one was missing and it's hard to find a replica. I placed a disc 1 cm foam 60 PPI just to protect the engine from particles/contamination.

Spark Plugs actually used: NGK B8HS

i try to find a device to check compression as you all suggest as next step

question:
1) i don t know how to check and eventually set properly the ignition time on my model. Is there any reference that i can follow?
2) heat range higher with the plug should help me to contain if i well understood. So it means that i should move to "cold type" of plugs. So NGK 9 or 10
3) could be also a problem of engine oil type used? personally i do not know what is inside.

[vechorik1373]

When it is running, look closely at where the head and cylinder meet. you could also have a blown head gasket on that side, if suddenly this fouling occurred. If you see ANY bubbles coming out between the head and cylinder, you have lost a head gasket.

[niall4473]

NGK plugs are no longer any good for anything which uses a choke or mixture richening for starting, because the vast majority go into fuel-injected cars, NGK have chosen to stop glazing the insulator which surrounds the electrode, so the first time the plug gets a rich mixture the porous insulator becomes impregnated with carbon and it does not burn off again, other manufacturers may have done this now but NGK started it. Old stock ones would be OK of course.
Another problem is that a good proportion of the 'NGK' plugs in the market place are generic knock-offs from SE Asia, and could be any grade at all, it used to be possible to spot them fairly easily, but no longer.

[DIS295]

Since you're using B8H NGK plugs, if you want to have a little more heat to burn off the carbon, the next hotter B7H is what you should try. B9H is very cold and has a heat range more appropriate for racing rather than street riding. Using a hotter plug will mask the underlying issue, and may get you through a season of casual riding, but it's not a good long term solution.