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Rob's WD16H and Big4 Forum

Dutch army, Johan Herman Fuhler, somewhere between 1945 and 1950

Rob's WD16H and Big4 Forum
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Best modern spark plug

I've been shall we say exploring the outer limits of my vehicle's performance.
Thus far I've established that the petrol tank filters needed cleaning and that the old rebuildable spark plug was breaking down going up hills. I'm still not convinced that the right hand cleaned tap filter is letting quite enough fuel through on it's own, or that the new plug is the correct heat range.
Since the carb seems happy at full throttle on the flat I think the main jet is correct
It may be that the engine just doesn't like lugging close to full throttle in top going 40mph up a long steep hill. It seemed to start pinking and was fine when I changed to third. It also seemed better when on another hill I had both taps open. I'd already sorted the blocked filter.
It's much revier than my M21 with a lot less punch in mid to low revs, but we are talking slugs and snails.
The compression is great and the magneto is new and timing good and it has stopped smoking [it hardly moved for 50 years].
I've cleaned out the float bowl and set the float height so that the revs no longer rise whenever I shut off the fuel taps; a sure sign that the float height was out a touch
I have a Champion D9 in it. Is this correct?
I consulted a pile of comparison charts but there appeared quite a lot of latitude as to which different make plugs were of the same heat range.

Re: Best modern spark plug

I've done some research and found that some specialists say to use a colder plug due to modern fuels burning hotter. The Champion is correct as per book. I've ordered a touch colder Bosch m5sc so we'll see how that goes. I'll report back in ten days

Re: Best modern spark plug

40 up a "long steep hill" sounds about right for a WD16H. Slightly retard the ignition on the advance/retard control to stop the pinking if you are convinced the timing is correct.

Re: Best modern spark plug

Thanks Keith I hadn't thought to do that. All My M21s have been far more sensitive to too much advance at low revs. The Norton seems not to need much retard at really low revs, perhaps it's engine is more sensitive under load. The last time I rode a 16H I was 17.....

Re: Best modern spark plug

Put in a Bosch M5AC. The previous plug showed signs of overheating
Starts fine and went up the same long hill at 45, from halfway up at almost full throttle
No pinking. Did not retard ignition. Engine seems more responsive hence 45 rather than 40. Happy