I've had trouble with my spark plugs fouling a lot on my 641. It does burn some oil, but doesn't smoke much once it gets warmed up and working. But every time I've worked it the spark plugs always had a dry, black carbon crust built up on them. That was using AL437s.
I tried NGK B4L spark plugs and the same thing happened. Not quite as quick as an AL437, but still fouled quickly. I don't have it running too rich. I run it as lean as I can without it stumbling when it gets a sudden load.
Got a set of NGK B2 spark plugs in there now. I've worked it twice and checked the spark plugs after each run and the plugs are definitely getting up to a high enough temperature to keep themselves clean now.
Yes, I probably need to rebuild my engine and intend to some day because it does have a little blow-by (mostly at startup). But if someone else out there has troubles routinely fouling their plugs then I thought I'd put it out there that NGK B2 spark plugs (NGK3110) appear to work well..at least for me. If you do NOT have trouble with 'colder' spark plugs fouling then most definitely don't switch. But if you do have fouling troubles you might want to give it a try.
I tried NGK B4L spark plugs and the same thing happened. Not quite as quick as an AL437, but still fouled quickly. I don't have it running too rich. I run it as lean as I can without it stumbling when it gets a sudden load.
Got a set of NGK B2 spark plugs in there now. I've worked it twice and checked the spark plugs after each run and the plugs are definitely getting up to a high enough temperature to keep themselves clean now.
Yes, I probably need to rebuild my engine and intend to some day because it does have a little blow-by (mostly at startup). But if someone else out there has troubles routinely fouling their plugs then I thought I'd put it out there that NGK B2 spark plugs (NGK3110) appear to work well..at least for me. If you do NOT have trouble with 'colder' spark plugs fouling then most definitely don't switch. But if you do have fouling troubles you might want to give it a try.