78 kz400 running rough, noob needs help!

Hey gang, just signed up HELLO! Glad to join a group that shares knowledge base. So I haven't ridden a bike in some twenty years+ but decided that it was missing from my life. GREAT choice. I acquired a 78 kawa kz400 b1, with 4,000 miles. It ran great at first, no problems other than my lack of skill lol... The first great morning for a ride to work after 3 weeks of rain, i got her up to 90 on the interstate. On the way home I opened her up all the way down the on-ramp. Now began the problems, seemed to run fine all the way down the highway, soon as a dropped to idle it sputtered like the carbs were unsinked and died. So i choke it a bit, to keep idle and get home.

So a friend suggests replacing the carb intake boots, get that done fairly easily. Now it gets interesting... First start and rip around the block ran great again! Took it down the road at about 45, about 4 miles, ran great! Got out with the girlfriend for trial 3, FAIL, back to sputtering. can smell fuel. Tank does have rust inside, and has no inline fuel filter added YET lol. Bit knocky on the right side too, but maybe i just don,t have the ears for the engine yet...

At any rate, if anyone has some pointers, I would love to dig in and fix it myself. I have spent some time helping rebuild my 63 caddy engine and tranny so I do have some skill. THANKS in advance gang:)

UPDATE: Just took her around block and it ran fine, so either a warming up thing or maybe the fuel cap vent is blocked???

It can be rust clogging the main jet that fall out once the bike sits for a bit and vacuum receeds. Or it can be a clogged vent, try opening the fuel tank lid next time you lose power. Or it can be that the fuel petcock is partially clogged and won't flow enough. Or it can be the ignition coil that fails when it gets warm/hot, causing sparks to break up.

Another possibility is too tight valve clearances.
Would measure and adjust as needed to within specs.

Typical symptoms include running okay while cold, but when warned up, the engine won't idle.

Good Fortune!

Thanks for jumping in quickly gang I'm inclined to think it's passing sea monkeys from the tank, and blocking their way through. i did swish up the tank real good before starting it. Three rides around town today , no problem. Getting an inline filter tommorrow! Found a local tank replacement woohoo. Think I will just give whole whole fuel system a good once over, finding the "step bys" pretty easily...