Hi BobA I replaced the air cut off valves in my Transalp.The symptoms were popping from the exhaust when slowing down,And sometimes when slowing down through the gears from higher speeds or comming down a steep hill through the gears it was like a shotgun going off.If you check the LINKS at the top of the page and go to service/Repairs and look for N.R.P. you will get the air cut off valves for around Half the price HONDA charge for them.When you take the cover plates off be very careful as there is a very small spring behind the plate WHICH is hard to find when it flys away.Francis:thumb:
Hi BobA not when idling Only when slowing down .Have you checked the rubbers from the airbox to the carbs as these have been known to pop off by themselves .When you check the Air cut off valves the material is very thin and a tiny hole or tear is enough to make the popping/Backfiring start.Francis:thumbright:
I initially cast my eye over the fuel system (aware of the carb rubbers) and didn't find anything untowards, so I started to check the electrics.
A few hours with a multimeter had me suspecting the loom or CDI, so I bought a spare CDi that came up cheap, but it didn't change anything.
Rooting deeper, I found some really bad bodges on the loom with dry solder joints that literally fell apart in my hand. I put all that right and fixed some other bad electrical bodges including replacement of a CDI connector with all new OE connectors from Beaver Trading, and I was 100% convinced this would cure it. IT DIDN'T!!!
Have a few other ideas, but wondered about air cut-off symptoms as I've advised people in the past that the valves may be worth checking and getting replacements from NRP.
I think I need to root around a bit more and possibly try a spare set of carbs on the bike to try and isolate this annoying intermittent popping. Bike idles perfectly other than that.
I replaced mine Bob and it did cure the problem :thumbup:
The valves make the fuel/air mixture leaner below 3000 revs so the symptoms occur below 3000 revs if there is a problem . As has been said, the worst of the popping (back-firing) occurs on the over-run on deceleration due to unburned fuel getting into the exhausts. I also found that the bike would experience a sort of cough every so often if I held a steady speed below 3000 revs. The third symptom was a similar cough if I blipped the throttle while the engine was idling (not every time though). Too much fuel in the fuel/air mix meant the spark wouldn't ignite it I guess.
I believe that RD03 and 04 cut-off valves are rebuildable and bits are quite cheap. 07 and 07A valves are sealed plastic units costing a hefty £75 each I believe.
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