Bonneville America Forums Forums Technical Forums Exhaust Trying to work it out.......

I have posted this thread on another site as well cheers.

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Hello everyone, I bought my Speedmaster late last year it was a demo model with only 10kms on it so it's never been ridden by anyone except the staff at the dealership for a road test.

Now this bike came fitted with TORS but ever since I had it at times it pops a bit on decel. Ok on it's first service I told the mechanic about this and he checked the fuel mapping and said everything was fine and told me these bikes can pop a bit on decel with aftermarket pipes fitted.

So I went to a mates house who does a bit of work on bikes and told him what was happening, he got me to start the bike up and he put his hand under each of the the pipes where the muffler and header pipe join up and exhaust gases were leaking out.

Ok easy fix I thought take it back to the dealership and get them to tighten up the joining clamps, but here comes the surprise when I told the mechanic about this he said if I look under the pipes I will see a small drain hole in the heat sheild so that if any water finds it's way in there it can drain out and thats why I can feel the exhaust gases.

I have had a look at this myself and yes there are a small hole in each pipe or heat sheild now I am not the smartest cookie in the shed but if exhaust gases can escape from these so called drain holes I am also sure that they can be sucking cold air back into hot pipes making the bike pop on decel.

So now I am trying to work it out why these pipes have been made this way, as I said most of us know that cold air been sucked into hot pipes will make the bike backfire and pop so at the moment I just can't see the logic in this cheers.

Bruce - Do you still have the AI installed? Is the O2 sensor operational? If yes to either of those questions then that is the reason for your popping on decel. Nothing to do with the drain in the exhaust. The popping is normal - for an AI operating in closed loop. If it bothers you, then disconnect or remove the AI and turn off the O2 sensors.

Thanks for your reply, yes the AI is still installed so yes come to think of it that would cause the poping with unburnt gases been forced back into hot pipes, I should of thought of that myself it's just that the drain holes had me stumped cheers.

I would also tighten up your exhaust header mounting nuts. I had to snug mine up several times. Did your mechanic state that the bike was set up with the MAP for the TORs? If it wasn't changed when the exhaust was switched, it will run lean and pop excessively.