This is not mine, but my buddies. We have a huge ride planned for tomorrow and his Z is running like crap. Here is the lowdown on what happened. First off, my buddy has the full Yosh exhaust system, smaller 12 tooth front sprocket, K&N filter & Outerwears cover. He never rejetted from stock and it ran pretty good, but he finally wanted to put a 170 in it, so 2 days ago he came over and we installed it. At first it was backfiring like crazy, he pulled his airbox lid off and it took off like a bat out of hell for about 5 minutes. Then it just started dying out like it was running out of gas. He got it home, and we messed with it but even during idle it felt like it was starving for fuel. So he replaced the the OEM jet and it still feels the same. Any clue on the problem. We are tearing it all apart today and he has the money to replace anything so please and advice would be very helpful!!! He does have a modified airbox lid to install with the vents when he went riding, didn't bring it to my house. Also, anyone know what size jet we should use if the 170 does not work???? Thanks again

 

Anyone??? I really need some advice on this is possible. We got a huge ride tomorrow and want to try to fix it by then. Thanks again for any help at all

 

Is the tank full, if not fill it. I would try runing with it on prime. The petcock is vaccume operated, there might be a leak or other problem.
You could try puting the old jets back in to check if its a jetting problem or something else.
The 170 might be a little big.

With a pipe/airfilter/no lid I was runing a 160 mikuni main, stock needle, stock pilot, screw ~3 turns out.