I av a 140cc pit bike and when the engine is off the gears work, when the engine is running i can get 1st but then av to force it into 2nd and 3rd any advice plz

Hello. It seems your vehicle's transmission has to be rebuilt/replaced. Any automatic transmission that won't 'shift' from 1st gear into 2nd or 3rd gear has a 'worn' slave cylinder that 'slides' gears one way or another. 1st gear works yet 2nd and 3rd don't. Good luck and keep me informed; if you want to.

2nd and 4th gear band is not applying. Possibly worn out. It comes on in 2nd and Overdrive. If this is the case, transmission will have to be overhauled.

gear selector forks worn. not an easy fix im afraid

Check the linkage firs if it is in the right place then you will need to rebuild the trans or get a new one as the bands are gone in it. Try to change the fluids and filter first. But from the sounds of it i would say the bands are gone and it needs a new trans.

The transmission "neutral" position is located between 2nd and 1st gear. You say you're also getting a "false neutral" between 3rd and 2nd. Since you say you're finding both, it leads me to suspect that you are not being aggressive enough when shifting the gears. The Sportster has the best shifting transmission of all the Harley motorcycles. Since it does shift so easily, riders sometimes "soft shift" the transmission and wind up missing gearshifts. This is the most likely problem, rider error.

Now, there is the possibility that the clutch is dragging but that usually effects the transmission when upshifting, not so much downshifting. With the engine off and switch on, put the transmission in gear, hold the clutch lever in, press the starter button. If the bike tries to move forward, you need to adjust the clutch.

Ride Safe
Steve

the function of the gears are to transfer and convert energy created by the engine into momentum

Sounds like a bent shift fork of broken dog gear. Try cleaning the inside of trans with part light oil and solvent. (not fuel) Rock bike a few times and shift gears, Do not start. Keep doing so untill shifting gets easier. If this does not work. Try starting it one time and shift easy. Do not force. Still no luck - Split cases and repair

STOP Downshifting!
STOP Forcing gear change, watch the Engine RPMs and shift accordingly, HOMBRE's are as good as the operator's. Hombre's have dash shift indicators which illuminate when it's time to 'shift' and not before, This has nothing to do with gear oil either. If you've drained it, you best fill it immediately and make sure it's ample level. The heat these gears sustain in is inceredible, cooling lubricant is essential. Here's a tip, while engine is OFF, ignition key is engaged, dash is illuminated, depress clutch peddle, keep it depressed and walk through all gears with gear shift, shifting should be smooth and unpeded, including reverse. If resistance is experienced at one or more gears, gear alignment is off as a result of inproper gear shifting while driving. Continue to drive vehicle just shift slower until clutch needs replacement then do an entire drive shaft upgrade. It worth it, it's great truck.