Jump to content
Sign in to follow this  

Jetting, Farts and dies coming off idle.

Recommended Posts

I have an '06 250x that was factory stock until this spring. I had the valves checked, then put on a FMF megabomb/4.1 exhaust system, cut the air box open, removed the fire screen, and installed an aftermarket filter. I decided against the pink wire mod, since I rarely come close to the limiter. I typically ride woods and trails in Michigan's Manistee National Forrest. A friend with decades of carburetor experience stripped, cleaned, and did initial set up for the mods, but he's a busy man and is difficult to get in contact with.

 

Initial Setup;

OE Keihin FCR

150 main jet

OE Needle 5th position

42 pilot jet

40 leak jet

 

After some testing, I went to a 45 pilot jet and installed a Merge Racing accelerator pump spring. I'm not interested in o-ring or wire tie mods to the AP system because I want it to be right, not rigged.

 

Today was my first chance to ride on the newest setting. It was stalling a lot just as I'd touch the throttle to come off idle and release the clutch to take off. Fart (backfire) and die. I've searched google and TT, but I've come up empty handed on a solution to the issue. With the 42 pilot it died occationally and seemed to lessen as i richened the fuel screw, I got to 2.5 turns and it mostly stopped which is why I went to the 45 pilot. Then today it was terrible. I tried it at 1.5 - 2.5 turns on the screw and it didn't seem to matter much. I'll be riding my usual trails tomorrow and will probably try leaning the fuel screw just to see how it reacts. I don't think its the AP circuit because above 1/4 throttle it ran very cleanly no matter how hard I jumped on it. That's why I'm thinking it is a Pilot circuit issue. Also, it was being a PITA about starting. Thank god for the magic button!

 

Any suggestions? Thoughts, comments, helpful insight? I'm certain I'm missing something, and I feel lost on which way to take it next.

Share this post


Link to post
Share on other sites

It sounds just like the bog that was so common on alot of the early 250's and was easily fixed by using the oring mod on the ap links.

 

Without a small shot of fuel at the right time from the ap it was to lean and would bog or stall out like you described.

Share this post


Link to post
Share on other sites

I agree with TDW. There is a fix for the off-idle bog, its a wired or o-ring AP arm, but the rest of the jetting has to be right for it to work right.

 

Here is what worked on our two:

 

55 LJ

AP link wired (I had an o-ring break early on when we only had one 250X and tried countless combinations and tracked em via an excel spreadsheet and nothing worked right until FINALLY I looked at the AP arm and found the o-ring was broken. I was like dang!!). Then I hit on the rest of this as golden for us:

 

45 PJ

Stock needle, clip on 3

148 MJ

Snorkel removed from airbox

Stock exhaust (we've since pulled out the baffle and its still fine)

05 R cam

 

That should be a good starting point. I'm at 6250' and jetted for up to 8500 or so. You are lower and have more free flowing exhaust but no R cam.. Perhaps the ticket will be raise needle 1 vs my specs. Perhaps it will be next size up MJ. Again, I think you'll be real close with my settings. I can run them down to 4200' or so and all still fine.

 

Needle on 5 is too rich. Trying to compensate for something....which is lack of AP squirt.

Share this post


Link to post
Share on other sites

All this sounds way more complicated than just riding around. It sounds like modding is very problematic, marriage is problematic but I wouldnt change it for the world so I guess I can relate.

Share this post


Link to post
Share on other sites

Check your hotstart cable isn't seized or your plunger raised. Sounds too lean to me.Hotstart cable can easily be guilty.

Share this post


Link to post
Share on other sites

Pilot jet is for idle only!!! You select the pilot based on the fuel screw response. Then fine adjsut the fuel screw and leave the pilot alone.

 

Assuming you did not screw something up that you are not telling us (like you removed the AP timing screw when you piut the Merge spring on and failed to reset it to factory (not a guess) specs.))

 

if you are off of idle, you are on the needle. The changes you made (removal of the air box screen, sort of pointless in your case to of done it) air filter and exhaust will not have any (or at least negligable) effect below 1/4 throttle, probably even 1/2. So for now, put the needle back.

Share this post


Link to post
Share on other sites

I would agree, needle at 5th way to rich. I've seen more bogging issues because of being too rich. I would try position 3 on the needle that will definitely lean up the mid and when you hit the throttle. I think most guys at your elevation probably run at 4, but going to 3 will give you better idea. I can change my needle on my 06 by loosening the carb boots and removing the the seat and some thin needle nose pliers and going from the top. No need to raise sub frame etc.

Share this post


Link to post
Share on other sites

I hit send on accident. .....42pj....155mj. ..Needle on 5th slot. I have tried the fuel screw at 2 1/2 out all the way to 4. Tends to want to idle.....but I have noticed that that the bike idles high and low on its own....not sure what that's about. Any ideas of what could help......thanks

Share this post


Link to post
Share on other sites

My 05 had a similar problem and based on AFR readings it is a lean condition in the transition for the low speed circuit to the needle circuit.  Two fixes that will help: Turn out the idle mixture screw 1/4-1/2 turn will reduce the leanness.  Add the O ring and the transition to the needle will be smoother.  JD provides two O rings in their kit, I'm using the smaller one.

Share this post


Link to post
Share on other sites

My JD kit had two different size O rings; a large #78 (7/16" OD x 3/32" thick), and a small (7/16" OD x 1/16" thick).

 

I bought some of the large rings at my local ACE hardware, but auto part stores usually have a selection of single rings behind the counter, just ask.  

Share this post


Link to post
Share on other sites

Chuck........so I some how fixed the issue but I dont know what did it.

 

1) when I removed the pilot jet it kind of "fell out". I barely turned it maybe 2 times and it fell out. Took me by surprise. (the jet was clean)

 

2) When I removed the fuel screw I noticed that the o ring was dangling at the tip. Is it supposed to be slid on the shaft somewhat? I ended up sliding it on some.

 

Shes idling great. I have a feeiing it was the o ring on the fuel screw.....any thoughts?

Share this post


Link to post
Share on other sites

Chuck........so I some how fixed the issue but I dont know what did it.

1) when I removed the pilot jet it kind of "fell out". I barely turned it maybe 2 times and it fell out. Took me by surprise. (the jet was clean)

2) When I removed the fuel screw I noticed that the o ring was dangling at the tip. Is it supposed to be slid on the shaft somewhat? I ended up sliding it on some.

Shes idling great. I have a feeiing it was the o ring on the fuel screw.....any thoughts?

I'd say it was most likely that your pilot jet was loose. The o ring on the fuel screw can sometimes stick in the hole when you take the screw out, which it probably tried to do when it came loose on the tip.

I still need some fine tuning, but the ballpark is that my pilot was way rich when I started the thread.

Share this post


Link to post
Share on other sites

Harleyd.....what elevation are you at in michigan?

~900 ft.

Right now I have. 45 pilot with the fuel screw at one turn out but I'm thinking I probably should have stayed with the 42 that was in it.

Harleyd.....what elevation are you at in michigan?

~900 ft.

Right now I have. 45 pilot with the fuel screw at one turn out but I'm thinking I probably should have stayed with the 42 that was in it.

Share this post


Link to post
Share on other sites

Harley....stay with the 42pj. Then try different positions on the needle.

My air box is opened up....cut the hole on the defuse inside the bike......I have 42pj....155mj....jd needle in the 4th position......I ride 0 to 4k feet. .....and she Flys through all the gears. ...no hesitation or bog.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...