2004 RSV Tuono backfiring after fuel pump line replacement

Hey folks,

My 04 RSV Tuono blew out its high pressure fuel line recently and I replaced it with the OEM part, and did the fuel filter and line to the outside with the parts from AF1 Racing. Since I've done that, it's taken to backfiring loudly on a slight bit of throttle opening.

In trying to resolve this, I've checked all the fuel lines and checked all the vacuum lines for leaks. None visible. I've replaced the air filter with a K&N (it was due), and pulled out the bung from the intake (ram air ducts side). I replaced the airbo gasket in case there was an air leak (it was a bit worn anyway).

The bike is definitely running richer... you really notice it at idle where it smells rich. I checked the idle air bleed screws and they were both a half turn out from fully tightened, which didn't seem enough, so I've pulled them both out to 1 1/2 turns - its smoothed out the bike a bit in the lower range but the idle still varies a bit and occasionally at idle (especially when cold) you'll get this hiccup from the engine, and a little "puff" sound fropm the exhaust - too much fuel I reckon.

Fuel consumption is up a bit - 180kms to warning light, when I used to get about 205 - 210kms.

I've thrown it into diagnostic mode and there's no codes. Throttle position 0 when throttle closed and 1 when you open it.

Any thoughts here? I'm leaning towards either:

a) the O2 sensor isn't reporting right; or
b) the problem with the fuel line had been around for a while and the previous owner has tuned the bike by tweaking the two potentiometer screws in the ECU to compensate and now the fuel pump is working fine it's too rich.

The performance of the bike when off idle is astounding - it will easily loft the front wheel in third gear at speed limit (its geared 15F 44R) - so this issue is only affecting the idle and when decelerating - the backfires are pretty loud - if it was just popping loudly I'd have no issue.

Obviously my throttle bodies aren't sync'd, and that is having an effect on the ropey idle, but I can't see how that could be causing the backfiring, and besides, it did that before I changed anything anyway.

Cheers guys.

Okay...

after two months of trying all sorts of things, testing all the lines, playing about with the idle air mix, and feeling like I was gonna have to give in and give it to the shop I've finally found the problem...

The giveaway was the vacuum lines on the gear lever side of the bike. If you squeezed the vacuum line for the rear cylinder the bike would die. But the front cylinder line... nothing. So there had to be some air getting in to the front cylinder injector somehow. And then I found it.

The fuel/air sensor for the front injector was sticking out just a little bit more than the one for the rear cylinder injector. Now, whether that was something that I did when I removed the fuel lines, or whether there's an O-ring that's perished that's let it come out I don't know, but it has had the effect of making the ECU think that front cylinder is running lean, which made it richen up the mixture in the front cylinder. End result - popping and backfiring on over-run and off-throttle, and higher fuel consumption. Not to mention a wandering idle that I had to sit at 2000 rpm because I'd wound up the idle air mixture to compensate. Now, the idle is back to 1200rpm, the idle air mixture screws are wound back to where they were, and it's purring like a kitten again.

To say I'm pleased would be an understatement.

Now I'm going to have to find out if these fuel/air sensors are supposed to be a soft fit or if there's some kind of O-ring that I need to replace.