Try taking out the emulsion tube/needle jet & checking if there is any build up on the outside of it or in it's bore, quite possible that the evaporated fuel has clogged up the fine holes

The needle jet is normally pretty easy to get out, remove the jet & washer that is screwed into the bottom of it & lightly tap it into the bore of the carb. Reassembly is easy, line up the groove on the outside needle jet with the pin inside the carb & slide it back into place

Does it wind up slowly or does it only rev to a certain point and no more? Rev slowly is normal,only rev to certain point could be clogged exhaust or air filter

Carb floats may be saturated if it sat with alcohol fuel for several months.

http://northover.com/Bike/YamahaTYManual.htm

Found this free 350 manual download awhile ago. Hope it helps.

Thanks Bird!

You're welcome.

I completely disassembled the carb again and soaked it all in SeaFoam overnight and then hit it all with the air compressor to blow out all the ports, passages, and jets. Both jets are clean, needle and seat are clean, float height is set to factory specs.

I did notice that my header exhaust pipe is cracked in the first bend after it leaves the cylinder head, but that shouldn't cause this issue I wouldn't think.

Air filter is new, and airbox is clean and unrestricted.

Carb has been cleaned and needle clip is in the 3rd slot, factory jets, emulsion tube is clean, and idle mixture screw set at 1 turn out from seated

Exhaust is not plugged up and it runs the same with or without the muffler on it

Compression test is 120 # on a cold motor

Spark is a healthy blue color when grounding the plug on the head

I sprayed carb clean while I had the bike running to find an air leak, but nothing evident happened to change the rpm of the motor while it was idling fine

It starts on the first or second kick with the choke on.

While it is idling, if I pull the choke to full choke, it will kill the motor.

My Dad said this bike had lots of power when he test rode it once before I bought it from him.

The only thing I can think of now is checking the crank seals behind the stator?

Any other ideas? I could really use the help to get this bike running great before the fall weather kicks in and it gets too cold for my wife to practice on this bike.

Thanks.

I talked with my brother who talked with my step brother that used to ride the TY, and he said that the bike runs crappy when you sit on the seat, but it runs normal when you stand up and ride. So with that said, it seems as though the seat pan when compressed is blocking all the air flow coming to the air filter. I did notice that it seemed to rev up better when I had it in the shop, and I was not sitting on it, but I thought that it was my imagination.

The air box is on the bike and the new air filter is in the proper position. Is there supposed to be something on the bottom of the seat pan that will keep it from squishing down and suffocating the air filter's air flow?

Edited September 3, 201213 yr by shooter308

No the only thing to do is to lower the brackets that hold the filter box from over the frame to under the frame. ( Mick Andrews's advise )

Guy