sputtering at cruising speed

i have a '78 kz 650 and i got it running and all tuned up and then suddenly it started sputtering at cruising speed and i have readjusted the timing and replaced the spark plugs and i don't know what else it could be any ideas or suggestions would be appreciated thank you

Next time it happens open your gas cap and see if that fixes the problem, if it does then the gas cap vent is plugged up.......worth a try.

1045

maybe check the fuel line for kinks and restricted flow. Clear plastic tubing is a b*gger for getting hard and doing that.

i modified my petcock and put 5/16 fuel line from both sides of the valve and i haven't noticed any kinks in either of the lines but ill look again thanks for the input.

I had a similar problem that I couldn't get rid of until I clipped up one notch on my carbs. This leaned out the carbs. You also might want to check the carb boots to see if you have any leaks, simply spray some WD-40 around the rubber carb manifolds when the engine is running, if the idle drops then you have WD-40 entering the intake runners due to a leak.

Cheers-Colin Firth-Ontario Canada