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backfiring on over-run

AlanNZ

AlanNZ

Cruisin' Guzzisti
GT Contributor
Joined
Sep 20, 2013
Messages
227
Location
Auckland
I was watching a video of a stelvio on YouTube the other day and noticed it was backfiring on the over run. My bike does the same. It's more popping than banging. I only notice it when riding without ear plugs. Is this normal or does it need a richer mix at idle? Exhaust clamps are tight so it's not sucking in air.
Alan NZ
 
The popping is caused by a combustible mixture existing in the muffler on closed throttle. Like you, exhaust system leaks were the first thing I looked for. A richer mixture at closed throttle might resolve it, though that will require disabling oxygen sensor input. Mine are disabled, and the popping is much less but still present. So I'm not sure how rich you'd have to go to stop it. Probably not worth fooling with. I just spent the weekend up at 7000' elevation, and the popping was still there. I did notice up there that the idle was noticeably smoother, so I'll likely richen the idle fueling a small bit, regardless of the popping. The correct fix for this which other manufacturers use is to install a vacuum operated idle air cutoff valve.

Stu
 
Yamaha uses idle air cut off valves on many of their bikes and the resulting snatchy fueling from closed throttle position is something they have been fighting with for years to try to eliminate with remaps of the Fi particularly on the FZ1. The idle valves are used to cut fuel during off throttle times and reduce exhaust emissions. The aftermarket has come up with solutions to add fuel and eliminate the problem but im sure they are for "off road only" and not a solution Yamaha could use, so I will live with a little popping on my Stelvio to not have another issue to deal with.
 
Age old story. Closed throttle decel pop is easily fixable, just takes a few $'s... via my Re-flash @90% resolution, or add a PC-V on top for 100%. In addition you will get a happier , smoother and cooler running engine, with zero cold start issues and zero detonation. Contact me direct for details, or see the various threads linked from the store on each.
 
there areseveral ways to get rid of this btw if you really care. add fuel to the ilde (on a pcv it is the 0 and 2%coloums like 15-30% to the pulse duration this is a lot of fuel] Or re-mapping the ecu adding a lot of fuel and setting the co to 7%, or on a stock map removing all the fuel below about 3,500rpm in the first three colums of the factory fuel table (the downside of this approach is engine braking gets really aggressive These all work but all have side effects
 
This is probably not relevant to Guzzi's but on my Suzuki 1250 Bandit 99% of decel popping was reduced by blocking the pair valve which is part of the emissions equipment and runs from the airbox to the valve covers. It could be done by using block off plates at the valve covers our by simply plugging the hose with a plug. I see my Stelvio has hoses coming off the head but don't know if its a similar system or just a breather on the Stelvio.
 
up north we just shoot barking dogs LOL - bad valve sets can add to the barking dog issue adding to the confused 02 sensors and at one point it came out of the dealership after the 15000km doing such that it blew out a exhaust gasket on the crossover pipe. Take Todds advice.
 
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