classic motorcycle forum

I've just colected my wife's heirloom. A 1937 Triumph 3/1 fitted with a 3HW engine. I know it has the wrong carb on it, and it's been fitted with Matchless forks and had BSA rear shocks welded into the rigid frame so it's not exactly concourse! In the 11 years it has been under a rolled up carpet it seems to have lost all it's sparks. I can srtrip and rebuild engines and major work doesn't faze me but if anyone has any info on this 3hw engine it would be helpful please. I have downloaded the original owner's manual but some good techno-detail would help.