bottom end bog, jetting help

[j-bo]

Bike ran good for a long time... just happened to start running badly.. found a ripped reed...

Now I have a bog on the bottom end, and the top end seems to not pull as far.

Im wondering if I should increase the main jet to a 172 from a 170 to help the top end rev out.

Also.. the bottom end.. no clue... I would suppose to make it leaner.. so backed out air screw 2 turns, which helped, but still have to clutch it to get bottom to "come on".

Bike is 99' yz250.... STOCK everything, except boyeson reeds.
Main 170
Air screw. started at 1 out, now 3 out.
power jet.. stock
needle.. stock.. 2nd position from top.

Bike has awesome mid range, just have to clutch it to come on. I need instant throttle response as much of our tracks jumps are right outta turns.

Thanx for any help. j-bo

 

[hunter1]

Try leaning the pilot jet, take it down a size. Then set air screw.

 

[j-bo]

How silly is this..
I found the problem to all my ills. The plug on the bottom of the carb. somehow got worn through on the edge. What it wore on I have no clue. But, it wore so bad, that the oring was exposed, which of course let air in and fuel out. All fixed now.

 

[Mike's 2003 YZ250]

:cool: Did you have to change any jets or mess with the air screw again after fixing the problem to get it to run right again?? Glad you got it fixed. :cool: Mike

 

[j-bo]

I put everything back to what it was originally when it was runnin like a champ. However, I did buy the bike used, and am thinking that the reeds were a lil bit bad from the get go, which was 2 years ago.
Now that I have new reeds in it, the top seems to be wanting more fuel. I will up the main jet to a 172 and ride wed. or thurs.
However, the bottom end bog is gone. I put back the stock pilot jet, which is spot on, and have the air screw 1 1/4 out, stock being 1 out.
So settings right now.
Stock needle, clip position.
Stock pilot and power jets.
One size leaner on the main (170) and gonna try a 172.
I am hoping that's what it is needing as I am now topping out on the topend a bit too soon.
I did look at the FMF specs, and it calls for everything I have, and even the 172 main which I will be going too.
I am using pump 93, 40:1 Silkolene PRO 2 sx.
Way down sealevel though, and of course, hot as blazes, with humidity to match. This should call for leaner settings, but I'm not finding that the case.
In the 2 years I've owned the bike, it ran pretty darn good on the above setting throughout without changing anything. Still hoping the 172 main is the ticket.
Hope this helps someone else along the road sometime.
Feel kinda silly I didn't notice the plug when changing jets.. Live and learn.