JAPs traditionally breathe only through the oilbox ......if you put breathers anywhere else ,you upset the lubrication system,and may even cut off the big end feed
That's pretty much my understanding too.
This bike "has" run well in the past, but was parked up for a few years (my Dad's health deteriorated and he died in '21, it took me a year or two to be ready for looking after the bike).
Last Friday I Took the JAPton out for a spin round the block:
It might run ok at less than 1/4 throttle, but any more than that and it starts bogging down, won't fire at all, then after 2 or 3 deafening explosions from the exhaust it'll pick up and run well for about 10 seconds or so before it starts bogging down again.
Rinse and repeat again and again if I try to ride it anything more than 1/4 throttle (ish).
I've been pouring over the literature I've got (the JAP books, and the AMAL tuning leaflet) and I still can't get my head around whether these symptoms are the carb set too rich, too weak, or something else completely.
The Amal booklet seems to suggest that issues with firing in the exhaust are ignition related.... But that doesn't balance with the fact that the engine WILL run properly for a few seconds before it bogs again, so I'm somewhat confused.
As I say, it'll run ok for a bit, then it seems as if something "builds up" and it stops firing, until the fuel in the exhaust detonates, and it clears up and runs again.... Until the "blockage" builds up again. That's what makes me think it's not ignition or timing - because presumably it wouldn't run at all at lower throttle openings etc if the timing had shifted?
Next thing I'm going to do is go over the inlet manifold and exhaust joins and check there's not gaps or holes in the system.
