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My Mototrans Owner's Manual lists a Firestone F20 EF-S spark plug. Now defunct, I can't find a cross-ref for an equivalent.
The bike came with a new/good Champion L86C but shows rich running wherever I have the carb needle height - UB24 with spec needle/jets as originally fitted.
I am wondering if its a hotter plug needed. Its a '61 engine with big valve head and '1' cam. I don't intend high revs operation.

Any plug equivalent or suggestions gratefully received.

I think that a B6HS or B7HS is recommended.

Thanks for that. I have looked for a reference,before asking here but didn't find one. As the current plug is hotter than those two, i'll have to weaken the mixture and try that.

The spanish parts catalog for the Mototrans 200 lists a BOSCH 225 (or equivalent Champion, no grade quoted).
The italian catalog recommends a 240 grade for the 200.

cheers Hans

EDIT: I found a spanish user manual on one of my harddrives. It says "F 20 EF-S (240 on BOSCH scale)".

Aye Geordie,

According to this online cross-reference, linked to below; the Bosch 225 plug, NGK equivalant plug is the B7HS and the Bosch 240 plug, NGK equivalent plug is the B8HS.

Spark_plug_cross_reference_link

At present I am running a B7HS in my '72 450 MKIII, rather than the often recommended B6HS that appeared too hot.

I believe Nigel Lacey runs either B7HS or when possible B8HS plugs in the race engines. He may care to comment?

Good health, Bill

Hi George,

Mine has a NGK B7 HS, you know the rest lol

Wow, what a response. Thank you to all. I'll get a new plug and start from there.

themoudie wrote:
At present I am running a B7HS in my '72 450 MKIII, rather than the often recommended B6HS that appeared too hot

Confusingly, I now find, NGK temperature reference numbers reduce for hotter while other manufacturer's increase!

That was my problem as well Geordie. Nigel suggested that I should be running B7HS or B8HS, rather than the B6HS that I had gravitated to, as this latter heat range plug was the type recommended in the Champion to NGK conversion tables. I too thought that I was using a cooler plug, whereas in fact I was using a hotter plug and starting to get blistering on the central electrode ceramic insulator.

Good health, Bill