Twin spark misfiring

hops

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My 2003 GSA has had a slight misfire for ages now but only when on a closed throttle and rolling to a stop or when pulling away from a stop. It would always clear when throttle was applied and therefore was not an issue. However over the last couple of days it's got worse to the extent that riding home last night it would not pull at anything more than a barely open throttle and even pinning the throttle back made no difference and it just bogged down and struggled to rev over 4000 revs.

With Steptoes help last year it was diagnosed with a dodgy secondary coil which was replaced as were both stick coils and the TPS unit. I did add a bottle of injector cleaner the other day which I'm now wondering if this might have been a cause but it revs with no problems when not under load.

I'll try some fresh fuel over the next couple of days but wondered if the problem may have arisen with any if you and diagnosed any differently?

The fast idle lever feels a little stiff but both throttle cables are seated correctly and the stops are both closing properly.
 
I had similar issue last year on 2003 twinspark. In my case after checking all else, the last thing I did was disconnect the return fuel line at the QD which then stops fuel returning to the tank. This virtually cured misfire and powerloss and pointed to failed pressure regulator return valve in fuel line. Once replaced, there was an annoying flat spot at 4000 revs subsequently cured by having injectors reconditioned. Worth trying the disconnect as it only takes a minute to check. If QD not fitted compress pipe with suitable grips. Good luck.
 
I had similar issue last year on 2003 twinspark. In my case after checking all else, the last thing I did was disconnect the return fuel line at the QD which then stops fuel returning to the tank. This virtually cured misfire and powerloss and pointed to failed pressure regulator return valve in fuel line. Once replaced, there was an annoying flat spot at 4000 revs subsequently cured by having injectors reconditioned. Worth trying the disconnect as it only takes a minute to check. If QD not fitted compress pipe with suitable grips. Good luck.

Will give that a bash, thanks.
 
Fuel pressure regulator changed last night, still the feckin same, grrr. Now where's that box of swan vestas?
 
Had a tinker with it tonight & it got steadily worse at it heated up so I'm leaning towards hall sensors, anyone else had similar symptoms and it turned out to be the hall sensors?
 
See if you can borrow a hall sensor plate from someone and test it (an expensive thing to change if you're not sure). Quite a few people have a spare lying around - I'd happily lend you mine (kept my old but working 35k sensor plate when I changed it before a long trip) but it's for an 1100 and has a different plug to yours.
 
See if you can borrow a hall sensor plate from someone and test it (an expensive thing to change if you're not sure). Quite a few people have a spare lying around - I'd happily lend you mine (kept my old but working 35k sensor plate when I changed it before a long trip) but it's for an 1100 and has a different plug to yours.

I've ordered a replacement Matt off eblag, thanks for the kind offer.
 
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Does this help with any diagnosis gents?
 
TPS unit ?
You really need a noide tester to plug into the injectors and see if they're getting a constant signal, you could try wriggling the wiring and plugs to the injectors and see of that makes a difference while it's running. And check the small metal contacts on the injector plugs are tight and haven't opned up.
 
tps was changed last year Neil, I might stick the old one back on just to try it. Thanks
 
Hops...don't know if this is of use to you as I'm in Harwich and from your location, you're Surrey, but if you fancy a ride up here, I have my '04 twin spark and she runs really well........You're welcome to spend a day playing- we can swap parts one by one then you can take yours for a run to see if we can pin down a part that's at the root of it.....I've got a few spares kicking around still as well (coil packs, injectors, primary coil etc)

Might be worth a go :nenau
 
Fanum, fab offer mate, really appreciated. If I could ride the bastard with any confidence I'd get down to Steppers but last time I risked it I broke down and had to get recovery home. I'll have another fiddle when I get a few days off and if need be I'll have to try and borrow a van or something to get it to the guru. Wish you were a bit closer, thanks again.
 
Well I never, after finding the inclination to investigate my poorly bike I've discovered the cause of the poor running I think. The link pipe inside the tank between the fuel filter and pump had a split in it which was not immediately visible with my dodgy eyesight but whilst testing the pump I noticed it squirting out of the split. This clearly reduced the pressure through the system resulting in a much reduced fuel flow.


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Mine did the same thing. Very hard to see but very obvious once dissected. I had a total power loss. I bet there are many Oilhead in-tank hoses ready to fail.

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I had similar issue last year on 2003 twinspark. In my case after checking all else, the last thing I did was disconnect the return fuel line at the QD which then stops fuel returning to the tank. This virtually cured misfire and powerloss and pointed to failed pressure regulator return valve in fuel line. Once replaced, there was an annoying flat spot at 4000 revs subsequently cured by having injectors reconditioned. Worth trying the disconnect as it only takes a minute to check. If QD not fitted compress pipe with suitable grips. Good luck.

Don't disconnect the return QD while the fuel pump is running! It's a great way to blow off or blow open a line in the tank. The pressure can easily reach 2X.
 
Well I never, after finding the inclination to investigate my poorly bike I've discovered the cause of the poor running I think. The link pipe inside the tank between the fuel filter and pump had a split in it which was not immediately visible with my dodgy eyesight but whilst testing the pump I noticed it squirting out of the split. This clearly reduced the pressure through the system resulting in a much reduced fuel flow.

Glad you found it, and hopefully before you'd gone too far down the expensive "Change it all bit by bit" route :D

It would have been a major pisser if you'd finally found it was that 4p's worth of hose after changing everything else :D
 
I seem to recall that U shaped hose being stupidly expensive when I refurbed the innards of my tank...
 


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