I have some Bosch sparkplugs that have WSR6F stamped on them. There is other printing on the insulator that starts with R10 and then three digits. They are all different. Does the printing on the insulator mean anything and are they usable in my 50cc engines? Dan.

The R means its a resistor plug which, given your (I won't say obsessive ) concern for radio interference is a good thing.

its a chain saw plug

Here's the cross reference to other plugs and I don't see the CM6 listed but hey, throw it in there and see if it runs, your motor won't explode.

http://www.sparkplug-crossreference....BOSCH_PN/WSR6F

Make sure to check it's reach length to ensure that it will not contact the piston.

Karol

Thanks you two. It's just what I was looking for. Dan.

The 6 range may be too cold. More likely use a 7 range plug
see bosch catalog http://www.bosch.com.au/content/lang...tralia_Web.pdf
page A14 a15 for type code markings

Been using those plugs on several Brison 3.2 engines for many years now and they work great.

Thanks pe for all that information. Thanks Bass. I'll be using them in Brison 3.2's. Dan.

Bass, I'll be gapping the plugs at .020 and I'm using a CH ignition. Is that what you're doing? Dan.

Dan, Yes exactly. I do have the R10 stamped on the insulator but I don't have the 3 digits on the insulator however I do see 3 tiny digits engraved on the base next to the engraved WSR6F- Brasil . My plugs are quite a few years old though (ancient).

Thanks again. Dan.