stuttering on hard acceleration

fenj66

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2004 gs in devon
hi all,
when i floor my gs1200, 54 reg, i get a stutter or hiccup from the engine as the revs start to climb.
its fine on normal/moderate acceleration but just does it overtaking when you snap the throttle full blast.
ive changed the plugs recently, the old and new were ngk irridiums, with no difference. ive filled up with premium fuel and no difference.
im getting 55mpg so happy with that.
when the bike idles its always felt like a four cylinder firing on three if that makes sense? but ive put that down to just being a trait of the boxer twin? but it pulls away cleanly evertime.
any thoughts on what could be the problem?

cheers.
 
so, just to tidy this thread up.
i gave each coil a visual check and couldnt see any problems like evidence of burning on the coil bodies.
i gave each one a good clean up and squirt of wd40 and replaced. no problems since!
hopefully the problem was a slight tracking under load from one.
a nice cheap fix for once!! ;)
 
I had this problem a couple of years back and was eventually traced to a hair line crack on one of the spark plugs. Only visible on very close inspection. Change all 4 plugs and has been fine ever since.
 
Had this problem with fuel pressure dropping to 30psi under hard acceleration from 45 psi at cruise. It should be 58 psi on a TC ( worn fuel pump bike done 42K ).
Your pre - TC should be 51psi 3.5 bar
Worth dropping a fuel pressure gauge on it and taking it for a run.
The worrying thing was that in closed loop the air fuel ratio was good the BMSK was adapting to the low pressure,but under full throttle (open loop) it was as lean than 18 to 1 soon be burnt valves !!
I see your problem is solved , just posted this for anyone with a similar problem that is not coils.
 
Also worth checking the external wiring connector for the fuel pump controller. Just checked mine this week and noticed the yellow rubber grommet missing, water had got into the 3-wire connector and corroded the pins. I managed to clean it with a fibreglass pencil and some contact cleaner then replace the sealing grommet with one from motorworks.

If the FPC can't run the fuel pump properly due to the above, its an easy fix.
 
If you suspect the fuel pump is weak, connect an FPC bypass cable. If the stutter goes away you'll know its a pump issue.

Caveats -
If your fuel strip is broken (indicating empty tank) the pump will be running at full power anyway
If the fuel strip is disconnected the pump will run at reduced power regardless of the tank fuel level.
 
With an FPC bypass cable connected the pump still would not make the 4 bar which the regulator on a TC is set at.
Just a couple of points that are probably stating the obvious.
when the mixture goes lean in open loop this puts a lot more strain on the coils which might have performed ok with a normal AFR.
When fitting a pattern pump to the original assembly revers flush the "sealed for life " fuel filter after the pump. I used a liter of petrol alternating between 100ml of fuel and compressed air.
Very surprised at how much black dust was in the filter it must of all come from the worn pump as the tank was clean and the sock on the bottom of the pump was clean.
Does anyone know the purpose of the green & blue wire that runs from the pump brown / -ve feed to the single terminal on the bottom of the "sealed for life " filter.?
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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