pash wrote:
You can attack it in two ways, either richen the mixture a tad (as you would increase the size of the slow running jet on a carb) or do what I do and pull the fuelling down by 20% at the TPS corresponding to closed throttle, down to about 2500rpm.
So, all good advice, especially if you have a pre-08 bike, however I had the opportunity to apply this to an 08/09/10 bike with a gutted exhaust belonging to a forum member here. To protect his identity, let's call him Dave...
I have known Dave for a couple of years, actually met him at the UKBEG party at BB a couple of years back. I had previously helped Dave get rid of the popping on an STT he had, dead easy, pull 20% of the fuel out at TPS equal to a closed throttle (and below) and job was a good'un. He had since got rid of his STT, moving on to an XT, and he gave me a call and asked if I could do the same again to get rid of the popping.
No problem I thought, so I took the stock maps:
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pulled 20% of the fuel out:
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then sent him out to test. He came back 20 minutes later telling me it was still popping, I knew he wasn't pulling my leg cos I could hear him coming back...
I thought maybe it needed more fuel taking out... So I took a further 50% out:
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then sent him out to test. He came back 20 minutes later with the same story...
This had me scratching my head as I had no clue why it wasn't responding to the fuel being pulled out. I need to be clear at this point, I don't have an 08/09/10 Buell so I am sure there was something catching me out here, some fuelling correction that was richening the mixture. If it was mine, I probably would have logged some data and looked at the injector pulse width, but I had another call to make to drop some X1 bits off later in the day, so I had another think. If it was a carbed bike popping and banging, I would go up a size on slow running jet to get the mixture to burn quicker, I could have done this on my Firebolt and Uly, but prefer the increased engine braking by pulling fuel out and the beauty of fuel injection is that I can make it lean or rich anywhere in the map, so I can ensure there is enough fuel close to idle...
The other option of course would be to start the combustion earlier on the over-run by advancing the ignition, so I looked at the ignition map and to my surprise I saw this:
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Check out the advance from 4500 to 2000rpm, there isn't very much compared to the cells above, no wonder it was burning late... This retard was probably put in to make the engine less responsive as it approaches idle, but really is overkill...
So, next thing was to give a bit more advance:
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I sent Dave out for a ride, and I must say I was a little concerned when he didn't come back after 30 minutes, but as he rolled in I knew we had cracked it, no popping, no banging and a well happy Dave.
Bottom line, my preferred solution for popping and banging on a DDFI-3 engine is to advance the ignition (on front and rear) at TPS=0
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