Twin spark won't idle and rough running

[Purplegerbil]

Hi, I have recently changed the fuel pipes and exhaust silencer on my 2003 twin spark. Checked cables seated at TB end
Started fine and ran well on fast idle.
Took it for a run and all was fine until I stopped for fuel, as I pulled into the garage and revs dropped it just cut out, no idle.
Started again no problem but wouldn't idle. I adjusted the idle screw to get an idle of about 1k, when shut off after revving it dropped to about 500rpm before gradually climbing back to 1k ish
This was intended to be a temporary bodge to stop it cutting out at lights etc
I carried on and it ran great apart from the tickover. On my return journey it started feeling rough at low revs and lost the tickover again, by the time I got home it was sounding rough below about 4k. The engine still felt smooth but sounded like it was stuttering and didn't like low revs at all, it also started backfiring when throttling off even slightly.
I won't get to look at it now until Sunday, I have my suspicions but any advice on what I should be checking will be gratefully received.

 

[sproggy]

Could be an air leak somewhere inboard of the throttle bodies making it run too lean?

 

[sproggy]

Missing bung off one or both of the throttle balancing stubs?

 

[oblertone]

By your right knee, always worth checking.

 

[Purplegerbil]

Thanks for the tips, I have Checked that cable and it's properly seated.
It was running perfectly prior to me removing the tank to change the fuel pipes. The only thing I intentionally disconnected was the r/h injector cable. I'm guessing I've somehow knocked something loose under the tank or it's just coincidence that it started playing around after the tank removal.
I can't put it down to the exhaust, none of the previous silencers I've had on it have made any real difference.

 

[DrFarkoff]

Thanks for the tips, I have Checked that cable and it's properly seated.
It was running perfectly prior to me removing the tank to change the fuel pipes. The only thing I intentionally disconnected was the r/h injector cable. I'm guessing I've somehow knocked something loose under the tank or it's just coincidence that it started playing around after the tank removal.
I can't put it down to the exhaust, none of the previous silencers I've had on it have made any real difference.

Make sure that all 4 ends of those 2 cables are all seated where they should be

If you look at the throttle quadrants that the cables wrap around they should come to a solid stop on the throttle stop screw IF there is an Airgap then the cables are not seated correctly

 

[Purplegerbil]

I will get the tank off again tomorrow for another look. Anything else to check like fuel or electrics ?
Would the throttle cables being unseated cause the symptoms it's displaying ? Would that have gradually worsened over distance ?

 

[oblertone]

I'd check the overflow pipes from the tank neck, and their route down through the bike. A pinched or constricted pipe could get worse as suction or pressure builds. Use a length of strimmer line to probe from the filler neck down, don't be tempted to use an air line as that can blow off a junction.

 

[DrFarkoff]

I adjusted the idle screw to get an idle of about 1k, when shut off after revving

Explain Idle Screw ??

the ones on the throttle stops (OH OH!!!!) or the big brass screws ?

Reading through it the Throttle cable thing was a red herring IF your bike started and ran fine initially?? Then the throttle stops were okay
IF it coughed and farted and messed about? Then the Unseated cables are good candidates

Open pipes do tend to drop the tickover but just a couple of hundred rpm

If you have it all reset back to the original settings??

1) Check the TPS setting is in the the 0.37~0.4 Volts value and if it is not adjust it to that

2) If that doesn't "help" just Unplug the lamda probe I have seen a few just crash and feed incorrect data to the ECU Unplugging it just sets the maps to a default base map

 

[Steptoe]

Twist the throttle full on with one hand, and with the other hand pull the throttle cable at the throttle body reasonably hard a few times, do the same on both sides… if the outer throttle cables have become dislodged at the junction box under the ABS modulator/battery carrier this usually snaps them back into place.

 

[Purplegerbil]

Thanks for the input, by idle screw I do mean the throttle stop, left side. I guess from the comments it's not going to be as simple as just winding it back to where it was.
I have found the problem. It's not the cables but the actual bit on the right TB the cable is fitted into, it's not returning under spring pressure but staying open. I can close it manually and it runs fine but as soon as I turn the throttle it sticks open, I guess this got gradually worse as I was riding. It only returns about half way from a fully open throttle.

 

[Purplegerbil]

Freed it up with some spray, it's now snapping shut as it should and I have adjusted the throttle stop again so it's tickover is at around 1k rpm.
I will have to have the TB off at some point to clean it properly but it's working for now.
Thanks everyone for the advice.