Help please..
I have just bought a 954, and it has an issue. when hot and idling it spits back randomly every few (5 to 10) seconds (it also hunts over 200 revs or so). It spits back so badly it stops sometimes.
Revs are currently set around 1200 but even at 1500 rpm it still spits back exactly the same
This only happens when fully warmed up.
I thought it might be the fpr diaphragm issue but disconnecting the vacuum pipe - no petrol came out and it carried on running exactly the same even when i blocked the vac pipe with my finger, and still spat back the same.
Firstly should it continue running with the vac pipe disconnected from the fpr?
secondly any ideas what may be wrong. seller says it was serviced recently with new plugs and was fine before i got it.
(i was thinking an inlet valve too tight or possible air leak somewhere, but haven't gone down those routes yet)
27k miles.
does have a pc111 attached but changing the mixture settings on it makes absolutely no difference to the misfire/spitting back/hunting so i doubt its that. I havent yet worked out if the flapper valve is still there, but it throws no error codes
thanks

Paul

 

I assume that "spitting back" means that the bike blows fuel back into the airbox?
Or do you have backfires?
Backfires most of the time mean that the iginition is off time.
Also a very common mistake with these bike is exchanging the MAP sensor with the TPS. These have the same connector and at idle it runs rough butit works.
Easy check: the injector cables and the TPS cable run in 1 wiring harness.
However you issue sounds different.
If I were you I would check the timing of the ignition.
Also; on the throttle bodies where also the idle screw is leading to, there is an actuator that works on coolant temperature. This is the idle enrichment. When this warms up it should close bypass valves in the throttle bodies.
You might want to check the functionality of that too.

If you dont have backfires, but air and fuel are pushed back through the throttlebodies I would be very worried about the timing of the bike.
This can be checked by removing the valve cover and the black round thing in the clutch housing.
If you are ready for that I can give you the Haynes manual procedure to check timing.

Another thing might be the crank angle sensor. It is mounted next to the alternator as far as I know. You might want to chack that one anyway, because almost all alternators are burnt. Light brown under and darker above. (mine was black and I missed a phase, it was shorted to the chassis)

But I'm quite sure it cannot be a difficult thing. These bikes are very basic in function and design.

 

thank you for a comprehensive reply. it spits back into the airbox. But not v often typically every 5 seconds or so. Sometimes every second but rev it and when it comes back its back to every few seconds... my feeling is fuelling. I have left but at a bike shop to investigate as workingl lots of hours this week and if its not sorted by next week the seller can have it back..

 

So bike shop decided they couldn't help.. I just ran it without the airbox lid and at idle the right hand cylinder certainly doesn't seem to have much vacuum compared to the others....

 

I returned the bike to the seller. Three weeks later the honda dealer still hasn't managed to sort it... looks like it's pretty serious.. not anything obvious...