need help guys

[justripit]

hey guys this is my first post and i am hoping im in the right place. first off ill let you guys know i have a 05 yfz 450 with a hmf slip on, uni filter, and no lid on the airbox. i got all that stuff about a month ago and had it rejetted and it was running fine. now just two days ago it started acting up by wanting to bog down. if i leave it over night i can get on it in the morning and ride for about 5 mins then it starts to bog. the only time it bogs is when the throttle is held in the same spot. if im in neutral i can hit the throttle and it will rev up fine but if i try to take off or hold it in the same spot it will die. i took the carb off and cleaned it good and cleaned all the jets. i checked my plug and it was fine also. i need some help guys i want to do it myself so i learn and it dont cost me an arm and a leg!! thanks guys

[Caseys 300ex]

If not that great in the engine department but it kinda sounds like its getting to much gas.

[GPracer2500]

Sounds suspiciously like vaccum lock in the gas tank. Check for a blocked fuel cap vent line. Also, when the rough running is happening, quickly stop and slowly open your gas cap. Listen for any air rushing into the tank.

If the tank isn't venting properly than the vaccum in there won't allow the gas to drain into the carb as it should. It's fine after it sits for a while because the vaccum in the tank slowly releases. Then it takes a little bit of running to build up that vaccum again.

Hope that's it! Should be an easy fix...

[justripit]

hey guys i checked out the gas cap and when i slowly took it off i didnt hear any air or anything like that. someone told me it may be my timing chain??

[GPracer2500]

If it had anything to do with the timing chain then I'd think it would happen all the time.

Did you check that the gas cap is venting properly? Listening for rushing air doesn't always work. The fact that the problem only happens after five minutes and only while being ridden really makes a fuel delivery problem the first thing to eliminate. I'd be SURE that's not the problem before I moved on to other causes.

Luckily it's easy to confirm that the carb is getting it's fuel supply normally. One good way would be to unscrew the float bowl drain screw. Let a bunch of fuel runnout. If it never slows down it's rate of flow then you know that's not the problem. If it eventually slows to a trickle then open the gas cap--if it flows again then tank vaccum is the problem.

[slvrlakerdr08]

ride it without the gas cap on once and see what it does then that will tell u whether its the cap or not

[justripit]

i tried running it with the lights on but still kills it at a steady throttle. i have checked all the jets, cleaned the carb twice, cleaned air filter, checked spark plug, checked gas cap vaccum, drained all the gas and tried newer gas but nothing has worked!?!?! i dont know what else to look for guys

[kfx400isdashiz]

i was givin a blaster that did that by a good friend of mine who moved away. i changed the petcock, put in a slightly smaller jet put a new free flow adapter on gas cap and higher octane fuel. the bogging stopped. so one thing was right.