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Xr650r jetting (sorry)

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Alright I'm hoping someone has maybe had a similar problem. Have an 02 Xr650r that I just put a mikuni tm40 pumper carb on yesterday. I can't seem to get it right, and I have a big ride coming up in a week and need to get it sorted out. After I got the carb I called sudco to get a ballpark on jetting, they said a 25 pilot and 145 main. Right now I have a 27.5 pilot and 140 main. Setup like this it runs okay but is a little lean at high rpm. If I run the needle in the middle clip I have a dead spot coming off idle. If I raise the clip one slot I lose the flat spot off idle but my high rpm lean spot gets worse. The accelerator pump is adjusted so that it hits the needle, and stops pumping right around half throttle. If I adjust the start of the accel pump at the the very start of opening the slide I get a bad bog. It gets better and better the more I delay the start, currently I am running it at the maximum delay and does great off idle, but only with the clip in the second position. I think the pilot circuit is about right, runs right at about 2 turns out on mixture screw. Think I just need a bigger main? The fact that I have to delay the accel pump so much has me all twisted up.(I've never dealt with an accel pump before) Everything I've read online says a 27.5 pilot should be fine. I'm in Southern California about 200ft elevation. On my ride in a week I'll be at around 8k feet, but I need to get it sorted st sea level before I know what I'll need at 8k feet. I don't have any other pilot jets on hand. I tried a 155 main that came in the carb and it was way too fat. Thats the only jets I have to fit this carb. I spent all day running around to different shops looking for jets and couldn't find anything, I'm going to have to order some on monday. Not sure what I'll order, just s 145 main like sudco recommends?Any help will be much appreciated 

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Are you near Huntington Beach?

Call them ask the parts dept. They wont have mikuni jets IN the shop...but will get you anything.

HB Honda

714-842-5533

If youre close, go through me at purchase Ill get you my discount. I wont even need to be there, I just have to give a parts guy a heads up that Im allowing someone to use my profile for the discount. 

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But I thought; main and/or needle. Whats the plug look like? 

You dont want the squirt to hit anything. Its supposed to get sucked in and burnt. 

Id say buy a few plugs, buy a few mains. Leave needle center clip. And see how different upping the main size is. 

Doing this all over again at elevation wont be fun either! 

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No I'm down in San Diego, i appreciate it though. I got all the jets I need today though through a shop down here. But I'm still getting conflicting results. My first test was with a 25 pilot and a 145 main in middle clip. Setup like this I can turn the air screw in all the way and it will have no effect on the bike. But my off idle flat spot is better than with the 27.5 and still having a higher rpm lean spot(not lean at full wide open, it's in the upper middle, at wide open itwould clear up and run great.. if I raise the clip one spot I can get rid of my off idle flat spot but my upper rpm flat spot gets worse. So, according to my train of thought, as I lean the pilot circuit my off idle flat spot gets better (Telling me I'm rich at the bottom) I also still have to delay the accel pump as much as possible telling me it can't handle that much fuel at the bottom(also sounds like maybe running rich at idle).but my upper mid rpm flat spot gets worse, (telling me I'm lean). After this I moved back to middle clip and decided to put 27.5 pilot back in because my upper rpm flat spot got worse with the 25. I also threw in a 147.5 main (just to see if it liked it) and boy did it, pulled like a train WOT. But my off idle bog was back. Raised the clip one more time to second position to lean it out and got rid of my off idle bog but my mid upper rpm flat spot was back again. I called it a night after that. I'm not sure where I'm gunna go from here. I think my off idle bog is the accel pump giving too much fuel and bogging me down. I think tomorrow I'll try the middle clip again and remove the rod for accel pump completely and see what happens. Unless someone has some input. During all this my plug was still on the lean side. I also haven't tracked down a 1.2 air jet yet which I've seen some people recommend. But it has a 1.1 in it now so I can't see that making a huge difference but maybe I'm wrong 

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Word.

I live in SD in Serra Mesa by Qualcomm. Holler if I can help.

Im unfamiliar with your carb specifically, but if it was an fcrmx, the leak jet being bigger would make less squirt. So maybe you need to work on whatever circuit that controls the amount/length of squirt. Lessen it. 

But thats a very minute amount of throttle opening, so if youre rich after 1/8th throttle, then its jetting.

JoeRC51, dont you have this carb?

And youre gonna have to redo ish up in elevation huh?  Grrr

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I'm going to play with it tomorrow, I may have to live with the occasional bog off idle for this weekend. I just ordered a different needle jet and jet needle that I've seen recommended a few times in different forums, along with the 1.2 air jet but I doubt they will be here in time for the big bear run this weekend. Yeah I'm going to have to re jet when I get to big bear around 8k feet. I found a chart that says, with some slight variation, that basically every thousand feet you go up you go down one size. So if I'm running a 147.5 right now at sea level then at 1k feet I would need a 146.5. And so on as you go higher. I've asked a few guys I know that have dealt with altitude jetting before and they all said that's a decent rule of thumb to start with 

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19 hours ago, notoriousE-R-I-C said:

Word.

I live in SD in Serra Mesa by Qualcomm. Holler if I can help.

Im unfamiliar with your carb specifically, but if it was an fcrmx, the leak jet being bigger would make less squirt. So maybe you need to work on whatever circuit that controls the amount/length of squirt. Lessen it. 

But thats a very minute amount of throttle opening, so if youre rich after 1/8th throttle, then its jetting.

JoeRC51, dont you have this carb?

And youre gonna have to redo ish up in elevation huh?  Grrr

I'm at 160/17.5 , 1.1 air jet at sea level. The accelerator pump linkage is adjustable for length and tip in point.

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Wow that small on the pilot? Mine was lean with just a 25. And wouldn't run at all WOT with a 155 main. Crazy how different it is. I finally got mine running pretty dang good today. Ended up with 27.5 pilot and 147.5 main in middle clip on needle and a 1.1 air jet. I disabled the accelerator pump completely and got rid of almost all of my off idle stumble. It would only do it at the very bottom of a gear lugging the bike around then grab a handful of throttle. But it changed from a bog to a cough like it wasn't getting enough fuel. So I gave it just the smallest amount of fuel from the accel pump I could and it runs beautifully now. No hesitation anywhere off the bottom and runs great wide open. I think I may need one size bigger on my main jet, but I don't have one on hand to try it, but it's on the way. I've ordered the 1.2 air jet, y1 needle, and y4 needle jet. So I'm probably going to be doing this all over again when that stuff gets in 

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When I received mine I had a similar issue although yours sounds not as extreme as mine was but after messing around for awhile I found a post from someone about accelerator pump nozzle size which prompted me to look into that and lo and behold the company the Power Barn had sent me a carb with a #70 I believe it was AP ( accelerator pump ) nozzle in it. they were nice enough to send me the one that should have been in there which was a #45.   I had disabled my AP to get the jetting right but then as soon as I would enable it would cough and bog, had it so it barely would engage and it would run alright but I knew that just was not right. now I have it set to squirt basically as soon as the throttle is moved and stay squirting for the max duration that it can. 

These are the final settings that I came up with and seems to be strong. Y 1 needle with the clip in the third position from top Y6 needle jet 142.5 main 27.5 pilot 45 AP nozzle set to actuate as soon as the throttle is moved and stay on as long as possible 1.2 air jet is what I was told is in the carb from the supplier                

Edited by C-M
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