When i crank my bike it runs but when i hit the gas it bogs down and dies nless i let off of it. why does it do that?

check to make sure the catalytic converters or muffler is not restricted

If you have any rubber fuel lines in the fuel system, I would replace them. Over a period of time the insides of the hoses swell up and stop the fuel flow to the engine.

'03 400 backfiring/bogging under throttle - ArcticChat.com ...

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Apr 3, 2007 - 7 posts - ‎7 authors The engine would only sputter and bog down, kinda like the choke was hung. ... I didn't remember the fan running, so I checked the fan fuse, but it was ... of the windings and cause a misfire, so bad that it would kill the bike. '07 F8 intermittent start and bog issue - ArcticChat.com
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try a new batt--or hav it tested for holdn 12.6v

Well there are more questions to be asked. Is your bike all stock? What ratio of gas are you running? And have you made sure your carb is clean

I have two ttr 125's and my son has another, all 05's but i ran into this with a friends 02 as well. All ttr 125's are cold blooded bikes to say the least. the cold starting procedure that works is to first lean the bike over to the left till it dribbles a little gas on the floor. hit the electric start for a few seconds only, wait 20 to 30 seconds and do it again. holding the starter button down and cranking will do nothing but flood the bike out. short busts only, dont give it any gas ever, this will also do nothing. first it will start for a brief moment then die, hit the button for about 3 to 4 revelutions and wait, the next time it will start again, most likely only for a few seconds again, repeat this and each time it will run a little longer till it keeps running on it own. the best way to get your ttr to start easier is to cut the top of the airbox off, this will give the bike more power (youll see why when you look at the tiny opening) and allow you to spray starting fluid under the back of the seat right into the airbox. it makes starting a cold bike 5 times faster. usually only 2 repeats of the starting procedure.

Hey pal, i got a feeling it's nothing like you think it is...the tank shouldn't lift without removing the bolt or bolts that hold it down...also many bikes have wires that run down the frame under the tank and here i where i think the problem lies....remove your tank completely, fuel lines, fuel guage wires etc... and set tank aside....now carefully inspect where your tank has been vibrating and rubbing on the wires, coils etc that are located there....take your time here as you will undoubtedly find a wire or connection that the tank has been rubbing on and now causing a short circuit......mend,repair, and insulate anything that has been damaged..then carefully reassemble and enjoy your ride....Good Luck to you friend.....Tim

Bogging down may indicate debris or old gas in the carb. Try doing a carb cleaning, and add a small amount of Seafoam gas additive to your gas.

If this is a gas engine, check the ignition coil or plug wires. A simple test...

Start the truck at night, then look under the hood while it's running. Don't use a flashlight or your headlights; it should be dark !

If you see sparks anywhere around the engine, you've found the problem. Now you can turn on a light to see where they're coming from - probably from a cracked ignition coil.

Good luck !

Marco

ase mechanic here, check for timing belt slippage, maybe clogged fuel filter, or low fuel pressure, mass air flow sensor dirysome common fixes for that year car.