Purchased for granddaughter bike ran so-so had to baby the throttle checked compression 110psi swapped plug bpr7hs put on uni air filter factory crumbled apart added boysen reeds while reed block was out ported it added fuel filter and cut off. Bike seems starved for fuel cleaned carb 3 different times same problem. Swapped carb from good running kfx 80 still same issue, other Kfx ran fine with this bikes carb. Ran with fuel line unattached from gas tank checked vent tube pulled top end to look at cylinder few score marks in cylinder and piston but all below piston ring line at bottom of the stroke sanded score marks out put top end back on took trans cover off while engine plastics still off started bike let warm up with choke on turned choke off bike wants to slowly die hit the throttle it dies. If u pull the choke up about 1/8 to 1/4 choke the bike will idle properly and good throttle response. Let it idle at 1/4 choke to stay running sprayed carb cleaner around total intake area throttle cable entry top end gasket areas behind starter gear and behindflywheel to check crank seals for air leaks. I've exhausted all the info found on here over the years this one has me scratching my head

 

To quote Damonsquad::
"I would pull the petcock off the tank and check the pickup screens, see if they are clogged or missing and the actual port is gunked up"
That helped a guy this weekend.
I've had to blow back thru the lines before.
Plugged pipe?
Motor not grounded?

 

Damonsquad's response is why I took the fuel line loose from the added fuel shut off, fuel filter and line full of fuel,still ran the same. While off turned petcock to prime fuel ran steady. Original pipe that came on bike had the baffle cut out and endcap welded back on,saw where u said usually doesn't do well I thought that might had been problem originally took spare pipe from my lt 80 put it on didn't change anything. As far as motor ground where are all the motor grounds located. While top end was off I noticed the port chamfering was a little excessive mostly on bottom side of windows, especially the window opposite exhaust port, its almost chamfered 1/4 " lower than window bottom just throwing this out there since u do port work

 

On the newer cylinders the chamfering is like that..No problem.
Motor ground is on the right side and is on the top front bolt that holds the fan cover on.
I add a extra ground.

 

have you checked the fuel cap/vent hose, if the hose is clogged, or the cap check valve is hung up with corrosion or rust the tank will get vapor locked and not allow fuel down to the carb in a steady flow. just like trying to pour a gas can without the vent open

 

I tried to eliminate the gas tank completely by pulling fuel line off and running with it disconnected return or pulse line still connected checked to make sure ground was connected

 

is the o'ring between the carb and the plastic spacer? they like to fall out or disappear. im wondering if the tank/carb is good, you may be having vacuum issues not sucking the mix into the cylinder.

 

O-ring is in, carb was swapped from good running Kfx 80 with no change put this bikes carb on good kfx ran fine. What does the secondary tank/carb line do pulse a diaphragm in the petcock when in on/reserve position

 

the petcock is vacuum operated when on run position, prime position will hold the petcock wide open, have you tried running it on prime? other then that i would say you have a spark or timing issue. timing issues arent very common on the lt80 tho, not many keyways breaking

 

Tried in every position if I pull the choke aprox 1/8 to 1/4 open barely pulling the plunger off its seat the bike will idle and rev right with quick throttle chops haven't tried with a weight load too much stuff hanging off it to try actually I tried holding the front brake with throttle w/o holding rear tire with other hand and it snatched it right out of my grip