KZ400 dying when driven 50mph+

Hey guys,

I just bought a kz400 from a guy on craigslist. I am somewhat familiar with motorcycles/ dirt bikes, so I went to take a look at the bike for sale and it ran perfect (other than small oil leak from rocker box which is pretty normal I hear) so I bought the bike. I ran it for 2 days real short distances around town constantly starting and stopping, bike ran great! then this morning I decided to take it to work which is about a 15 mile ride. I stayed on the feeder the whole time and didnt go above 55mph after about 3 miles of straight cruising 55mph it started sputtering like it wasnt getting enough gas, then after about 20 seconds of doing that it just lost all power and started decelerating. I pulled the clutch to shift to neutral, and it died immediately. So i pulled over and got off the bike looked around for a minute to make sure everything looked ok, everything seemed fine, got back on the bike and rode off. about 2-3 miles later same thing again, pulled over tried to start the bike back immediately and it wouldn't start, gave it a couple minutes to cool and started up just fine and I took off again. It did this 4 times on my 15 mile ride to work.

If any one has ANY ideas of what this could be it would be greatly appreciated.
Thanks!

Make sure your gas tank vent isn't clogged up. Does it make a difference if you open the gas cap when it's dying? Also check your fuel filter if you have one

Make sure the battery is good.

I dont have a fuel filter. But ill check the vent and see if the problem stops if the gas cap is open this afternoon.
The battery is a little weak but i didnt think that would matter. Not saying your wrong at all, I'm just curios, but what would the batter being bad or weak do with the bike not running at higher speeds?

I greatly appreciate the input guys. I will let you know if the vent fixes the problem and maybe try to charge the battery and let you know how that went this evening.

The bike needs a good, fully charged battery to run right.
Use a digital multimeter to check it. VC97 = good, inexpensive.

High beam test. Engine off. Charge the battery then disconnect the charger. You should have at least 12.6 VDC but the voltage will probably be higher ~13.1+. Turn on the high beam (engine off). The voltage will drop. A good battery will drop to ~12.2 VDC but ~11.85 is okay. If it drops to 11 VDC, the battery may need replacing. If it drops to 10 VDC, the battery is probably shot. The high beam test removes the surface charge & gives a better indication of the deep charge, or something like that. The voltages are the numbers I use. There may be a more accurate set of voltages on the internet somewhere.

Kink in the gas line between petcock and carbs?

+1 regarding the battery. But I think you may have a fuel supply issue. Start with the vent, like others said, then check for good flow from the tank by removing the fuel line from the carb and drain into a can. If all that is good, you may have a low float setting.

awesome, I hope it is an easy battery or fuel line fix. This has had me very worried, thinking it was going to be a huge problem. I am going in a couple hours to check the bike and charge the battery. I will let y'all know how that goes this evening. thanks again everyone for the input.

I dont know what your petcock looks like but there might be a little catch-cup on it you need to clean too. It just unscrews from under the petcock.

So my battery is a little weak but my charging system is great so I left the battery alone. I found out it was my petcock. I cleaned it out real good and its working now. I want to go ahead and replace the petcock though so it doesn't happen again.
Does anyone know where I can get a 1974-76 kz400 petcock?

No eBay APP ID and/or Cert ID defined in Kunena configurationWill this work? Ed

Chaseklewis wrote: So my battery is a little weak but my charging system is great so I left the battery alone. I found out it was my petcock. I cleaned it out real good and its working now. I want to go ahead and replace the petcock though so it doesn't happen again.
Does anyone know where I can get a 1974-76 kz400 petcock?

Replace the battery if it doesn't fully charge or hold a charge.