Crazy KZ750 Twin - Cannot Figure Out This Fuel/Stall/Surging problem

1977KZ750 B1 Twin

1 month ago the bike started surging and cutting off during riding. Not electrical, but more like fuel starvation
Carbs had never been rebuild since I bought it from the PO 3 years ago
Had the carbs rebuilt by a pro oldtimer in my area. His rep is golden and he works on only japanese vintage bikes.
Tank was clean, no rust, but I noticed when on RESERVE fuel would only come out of one tap constantly, and the other not constantly
Tank cap vent is unblocked. Fuel lines are clear.
Cleaned the petcock. Blew air into the openings and it came out through the bowl.
Put the rebuild carbs on yesterday and the bike ran like a champ. Let it sit overnight
Today, started out good, but started popping on decel, then sounding boggy, and surging like a damn racehorse.
Only by turning the petcock on and off did it stay alive.
There is no issue with the carbs. They were properly rebuilt.
Can a petcock flow fuel in the ON and RESERVE position and STILL be messed up?

Im fed up!

IF! it is a fuel supply issue i would check the fuel cap vent and the fuel tap filter and internal seals for blockages or damage and also for kinks in the fuel pipe.

wrote:

IF! it is a fuel supply issue i would check the fuel cap vent and the fuel tap filter and internal seals for blockages or damage and also for kinks in the fuel pipe.
 

Already checked all of that. I neglected to mention, Fuel cap vent is unblocked. Fuel tap doesnt have a filter. PO took it out. There is NO WAY to get into the petcock. I tried. Only the lever comes loose and the bottom bowl unscrews. I cant get inside the petcock. Looks like this the photo below.

There are no kinks in the fuel line. everything was changed to brand new when the rebuilt carbs were put in. Im thinking its the petcock but if its flowing fuel can it still NOT be working?

Both outlets should flow evenly.
The fact that one is intermittent shows that there's an internal problem which is starving one carb.
If you can't split the tap to fully inspect it or find a replacement then try fitting a fuel tee to the free flowing sides pipe to feed both carbs and see if that helps.

 

Thanks for this! I dont want to get one of the cheap China knockoffs. I have heard they are terrible
 

When you are checking the tap flow are you checking directly at the tap? If you are checking by disconnecting at the carb end of the fuel line then the filter being fitted with the flow direction in the wrong way will cause all your symptoms. 

None of this has to do with the filters or their direction
There were no filters on this bike at the time the test was being done.
The filters went on AFTER the rebuild. When I first suspected the petcock, I took the tank off, took the fuel lines off and turned the tap ON and watched the fuel come directly out of the tees. no filter, no fuel lines, just directly from the petcock taps