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Brhaap!
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Discussion Starter · #1 ·
I'm looking for some help from people who know their way around jetting. 2015 Beta 500RS which has a FCR39. I've been getting a lot of stuttering/stumbling while cruising lately. Bike is hard to start with choke when cold. Starts up instantly with no choke. When I pull away from idle, it feels very lackluster. Idle bounces up and down as well. All I've done so far is move the needle clip down to the fourth notch and adjust the float level. Any help would be appreciated.

Stock jet settings for my Beta.
Main - 180
Idling - 45
Starter - 85
Needle - OBDVR
Needle Position - 3
Main air - 200
Idling air - 100
Mixture screw - 1 1/2 turns out
Intake jet - 40

And the float level is set to a little above parallel with the carb body.
 

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The choke thing says perhaps the pilot is too rich. Wont fire up on the choke (way too much fuel) but fires right up without the choke (receiving plenty of fuel as if it's choked even though it's not"

That indicates too rich on the lower circuits (idling jet aka pilot jet). And that being as it is you also might have the needle a bit high. The needle lifts when you open the throttle. If its too high and lifts too soon before the engine is turning fast enough to gobble it down. What happens is you whack the throttle and your engine says "whoa what am i supposed to do with all this fuel at 2000 rpm all of a sudden?". So you get just like you said lackluster performance. So much fuel it's taking up some necessary air space in the combustion chamber. The engine isn't drawing in quite enough air to accompany. But you may be able to lower the needle and help the problem.

You may have actually taken the needle the wrong way. try the clip at center or above. 2nd groove from top

I'm not a whiz on the subject. Ive only had my stock bandit carbs apart a bunch of times now. Starting to learn what works and what doesn't. Admittedly though It looks like your carbs have more jets and adjustments to be made.

The easiest thing to check for quick results is the mixture screws. take them half a turn one way. problem better or worse? try them the other way then. you can always set them back to 1 1/2
 

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Brhaap!
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Discussion Starter · #4 ·
No worries. Thanks for the info. I think I've found a big reason why the bike has been running poorly lately. Checked my valves the other day and both exhaust were out of spec and the intakes were at the bottom of the spec. Need to shim them first then I'll tackle the jetting.
 

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sorry. I'm sure you're looking for more than that. dont mind me. Someone else feel free to jump in.
All accurate and helpful by my account.

No worries. Thanks for the info. I think I've found a big reason why the bike has been running poorly lately. Checked my valves the other day and both exhaust were out of spec and the intakes were at the bottom of the spec. Need to shim them first then I'll tackle the jetting.
Good on you to dig deeper, you know as well as I, you can chase your tail forever with valve issues.
 
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Another thing I noticed. If the bike is a tad on the lean side it will have a quieter muffled exhaust note (and hesitation). You might have a racing exhaust on there and it might be just as quiet as stock if your jetting is lean. More of just airy rushy sound. Engine will run like shit cold until absolutely warmed up. Then it maybe might do ok.

If you're jetting is on the rich side. the bike Will have a more obnoxious loud juicy sparky pissed off wake the neighbors exhaust note. also hesitation. Engine will run better cold and like shit once it warms up. Might run great in the first 10-15 minutes but after it gets fully warmed up the pull just isnt there. Especially on a hot day. But on a cool night It might run ok. Thats too rich.

get it somewhere in between with a healthy pull and you're getting there. Ive got mine just a tad on the lean side. It's super quiet with my 2 brothers exhaust and it doesn't quite pull like it should on a cool night. That's when it should pull it's best but it's a bit much on the lean side. So I need to go the opposite of you. Raise my needles maybe just one more shim. I may also need smaller pilots. Which may sound weird but there is a balance between it all.

I also need new intake boots and a sync. bandit stuff.
 

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Brhaap!
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Discussion Starter · #7 ·
Shimmed both exhaust valves and that seemed to have made a big difference. I received my JD Jet Kit as well and they recommend a 172 main and 42 pilot/idling jet plus their red needle on the fourth notch. Will be interesting to see how this plays out.
 

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Brhaap!
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Discussion Starter · #8 ·
Threw in the 42 idling, 172 main, and red needle (fourth clip). Well the bike still starts up without choke so I don't know if that's necessarily bad or not. Before I put in the kit, I thought the 172 main might be too small and I think it is. Before with the 180 main, 3/4-WOT pulled hard and now it feels kind of flat. I'm going to raise the needle one notch and see if that richens things up a little.
 

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Maybe like you said throw the 180 back in there. Try to stick with one change at a time. As tempting as it is to make several changes while you have the carb off. It can lead to confusion about whats working and what's not and which direction to go with which thingy.

granted you were starting at their recommended default. Now that seems a bit lean on the main. You could be right on the money. So try just the 42 pilot now. 180 main back in there. needle wherever they said still. is that 4th notch from the bottom or top? I would assume clip at the next notch down from the top of the needle. If the default clip setting is below center that would be weird... like "why dont you just make a shorter needle ya fuckheads"
 

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Brhaap!
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Discussion Starter · #10 ·
Correct. Fourth notch from the top is what they recommended. I was thinking move down to the fifth first before swapping the 180 main back in but I think I'll just do the main and leave the needle as is.
 

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you shouldn't have to lift the needle all the way away from the jet. Just try the bigger main back in there. Clip in the middle or one next to it.
 

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Brhaap!
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Discussion Starter · #12 ·
I went back to the settings that JD recommends and readjusted the float to Keihin's spec which is 9mm instead of Beta's which was parallel to the carb body. Initial impressions were this cured the sputtering issue I was having and pulls hard but I spoke too soon because it still does it. Happens at part throttle and goes away as soon as I give it more gas.
 
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