2005 YZ250 is firing on 5th gear decel

i ride at the dunes all the time and it puts a lot of extra load on the engine even when you think it's not that much it is. my bike did this the first time i went to the sand dunes my bike was a 95 yz250 and it did what your are talking about just kinda wanted to keep going for a while and when i would go o use the kill switch it would kinda diesel for a couple seconds then die. this is because it is really hot and you need to go up a size or two maybe three on your main jet to richen the mixture then your bike will run even better and scream up the hills. worked for me if you have a kehin pwk carb you can just loosen the boot screws securing it and without even having to take it out flip it on it's side so you can see the bottom and there will be a plug just undo it and there is your main jet i change mine back and forth depending on what kinda ridding im doing. but i would for sure go richer so you don't have to worry about the bike burning up on you. also what mix were you running i would say 32:1 is a good one to use at the dunes also check your radiator to make sure it's full mine boiled over one time and my bike ran like crap then i refilled it and it ran awesome. hope this helps.

did you ever see that carb vent kit sold in dennis kirk its almost air tight in your float boal and when you go over big jumps and whoops at fast speeds sometimes the fuel gets pushed to the top of the floatbowl and you spray way more fuel in your reeds.

float bowl sorry

did you ever see that carb vent kit sold in dennis kirk its almost air tight in your float boal and when you go over big jumps and whoops at fast speeds sometimes the fuel gets pushed to the top of the floatbowl and you spray way more fuel in your reeds.

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is that the one made by PC racing?

I had a blazer in high school that would almost die going through woops too fast

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You mean the car? Chevy Blazer? Through the whoops? F'n sweet man!