High Speed misfire
 

This is driving me crazy, cars been running fun for months and has suddenly decided to throw it's toy's out of the pram. Once the engine is warm when I hit around 80 - (who me officer? oh no I couldn't have) motor starts to misfire, back off and it stutters for a while and then clears if I cruise at 60 ish. It struggles under load so hills make it miss as well. I did have this a couple of years ago and it was the crank sensor wiring. So I've replaced the crank sensor, plug and wiring but problem persists, I've done plugs and leads and coil is about 18 months old.
Interesting in that the crank sensor wiring I took off had no shielding but worked no problem

Carbs have neen stripped and cleaned but I'm still inclined to think it's electrickery related Current set up is blacktop Zetec running GSXR600 carbs, and megajolt on base map. As I say the motor has been sweet as a nut for the last 6 months and I haven't tinkered with any settings so I know there's summat up! Ideas?:?

Bike carbs are not well suited to a car engine, you need an expert to map it.

Thanks but the carbs are set up well - been running them for the last 4 years with no problems, doing between 10 and 15k a year on them, the problem has only just raised it's head so I know something has failed.
I've found the carbs reliable (once we'd sorted the mixture) and they fit in a very limited space where I couldn't get either standard injectors, throttle bodies or Webers to fit

the thing is with bike carbs they are proned to water i no you said you stripped and cleaned them unless you blow through every piece wit an air line when you give it the gun the water gets sucked up the jets but cant go through when you back of water being heavier than petrol drops back down only takes a bit or missed a bit with the air line i got a zzr 1100 had to clean them twice try new plugs as well they dont like loads a fuel ray

Yep water is always a problem especially as it can condensate in the alloy tank but the've been stripped sonic bath and blown through - I have had a thought though, couple of years back my Triumph was misbehaving - ok when cold but would start spitting at higher speeds, then clear - tried loads of things to sort - plugs - leads- ecu and even had the head off and skimmed as a local dealer advised the head was blowing slightly. None of it made a difference - finally traced the problem to worn needle seats, two out of the three had worn oval so were screwing the mixture - So current set up has probably done 50k miles and I'm running very short filters and lots of vacumn so this may be the problem.
Not allowed to play with it tomorrow but got the all clear for 26th - so carbs off and have a look at the seats - I'll update once I've had a peak!
Cheers

check the diaphrams as well you can get some pellat type things to go in the tank they stop the water there very good im told

Been a bit of a delay as been in for urgent op - but back out now! So yep needles out and all the seats are worn egg shaped, to cap it all the carbs I use are one of the few you can't replace the seats in! So I found a new(old) set of similar carbs with no wear - and will bang these on - only problem I'm having at the moment is that the new needles are much thicker than the old ones - I'm guessing someone has tweaked the old ones with a dynojet kit - so looks like I'm going to be using a bit of fuel while I run up and down the road sorting the jetting........again! Beginning to think next move may be back to a single carb!