Realise BSA forum but wonder if anyone can help with my 1971 T120R OiF Bonneville since its a very similar bike to the later A65L OiF which I had in 73 and was a brilliant bike in my opinion. Also my 1970 A65 pre OiF doesn't suffer the problem outlined but is very similar to the T120 in terms of maintenance (new coils, new carbs etc. regular service and so on) and goes well under equivalent conditions to those described. T120 has electronic ignition which is about 15 years old. New twin AMALS, new 6 volt coils and spark plugs. Valve clearances fine and cylinder head correct torque to new gasket so should not be sucking in air through gasket joint weakening mixture. Bike starts easily and ticks over fine. Near top of hills it loses power where is a long climb getting steeper and the hill is slightly higher than usually causing the engine to work hard. It accelerates well at bottom and initial climb. My normal test to see if my fettling to solve problem has done any good here is Caerphilly mountain (for those who know it)- it is relatively steep at top and about 889 feet high so not exceptional by any means for some sort of air starvation. Air filters cleaned. Bike accelerates well as said on lower slopes but at top bike just loses power and have to change down to 3rd even 2nd. It might be on one cylinder by this time but can't really tell in the general slowing down and can't really hear with helmet and slightly deafness. When pull into the car park after a short flat section ticks over fine and restarts easily on kicking over and comes back home (down the mountain) with no problems despite a number of short climbs. Hope someone can help as you can imagine its very frustrating and trust you will all excuse a Triumph post on a BSA forum - excuse is do have an A65. Enjoy a safe weekend and hope weather is fine. Cheers, Hugh