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#89043
@stinkwheel

I think this could well be the problem as you said in the other thread retarding the inlet cam could help if there's enough clearance

Hopefully he will get it sorted Dai
#89044
Retarding the cam should help with clearance as the valve head doesn't arrive any where near where the piston crown was for another 18° at the crank.

But I think we've missed something else, NGK 6 plugs are recommended for the EFI/UCE models, but for a 612 classic Bullet engine we need a colder plug, try a B8ES or B9ES depending on the compression, or Champion N3C.

A.
#89056
Missed that with the plug

Also over thought the cam timing too used to one cam running both followers

For the price of a oil change and plug.
Retard inlet cam Bullet Wisperer's video shows exactly how to do it
Lift carb needle
Use high octane fuel
Fit colder plug

That lot won't take long to do and will help the bike run cooler and that should in turn help the clutch
Not forgetting the performance gain at higher revs

The valves would only be in danger with a higher lift inlet cam and that would be reduced by retarding the inlet cam

Has everyone seen Bullet Wisperer's latest video of the 1939 250 AJS thats impressive that is
Great to see you cracked that one Paul great job
#89062
Hope it stays together as well as the one I rebuilt back in the late 70s

They were a nice bike one of those where the Japanese didn't just chase speed

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