ZR-7 misfire

[jjdugen]

Hi
Got this one in the workshop at the moment. Guy has just boght it so has no believable history. Showing a believable 5500 miles.
Its been fitted with a pair of Viper type cans, not straight throgh but not exactly quiet.
Ticks over and revs fine off load, misses like mad on acceleration and cruise at 30 -40 mph.
It had a dynojet kit fitted bu the plugs showed very weak mixture. Replaced the standard needles and jets with an extra washer under the needle to richen the off throttle response. No change to the misfire, but, cyls 1 -2 are a good mixture, 3-4 weak as Hell.
Carbs thoroughly cleaned, pilots dead right, carbs perfectly balanced, all hoses, carb boots checked, no diaphram damage. I even went as far as to put extra washers under the weak needles, still no difference, No exhaust purge stuff on this, just the usual rocker vent into the airbox.
I cant believe that the valves will be out at this mileage, so, before I have to go in to eliminate that as the problem, anyone had one of these and can give any insight?
Cheers

[0l0dom0l0]

Is it okay after the misfire? Ie does it rev up to the redline or just sort of stop?

If it won't accelerate past that I'd put my money on fuel starvation to the two weak mixture carbs. Have you checked the float height and that all carbs are getting good fuel?

Might be the hoses is blocked or something.
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