Carb tuning help (yes, I've searched)

[THE BIG SITT]

My bike is still acting up after all of the tinkering I have done. After installing a pod filter, I went through and did all of the steps in tuning carbs that I thought were necessary. I changed the jets, shimmed the needles, adjusted the idle mixture screws, adjusted the idle with that knob on a cord thing, and synced the carbs (so I think).

With all of these things being done, my bike still has some power loss at the low RPMs (idle to >3000).

Here are my carb settings:

YEAR:2008

INTAKE MODIFICATIONS: K&N pod filter

EXHAUST MODIFICATIONS: DanMoto slip on

JET KIT OR STOCK? Jet kit

BRAND OF JET KIT? DynoJet

MAIN JET:110

NEEDLE AND CLIP POSITION: 4th

MIXTURE SCREW SETTINGS: ~2.5-2.75

ELEVATION: 800ft


What do you guys think could be the cause of my loss of power?

[alex.s]

have you seen this graph?

http://www.3cyl.com/mraxl/manuals/carbtune/carbtune.htm

[THE BIG SITT]

I have. What would you infer from that chart? Because I'm still clueless...

[alex.s]

dont get me wrong im a total noob when it comes to carb tuning... is the low power spot at any throttle position? are you testing this on a dyno or butt-dyno? 3k is pretty low... someone once mentioned the higher flow you optimize for, the more you lose at low-flow... maybe this is what you are seeing? you said yoou had pod filters. does that mean you removed the venturies or are they larger pods with venturies built in?

[THE BIG SITT]

I notice the power loss when accelerating from a stop. There is a distinct sputter at loss RPMs, but I don't know the difference between running too rich/lean...

[Jinx250]

Define "power loss" as you see it. FYI - the 250 has zero "power" in that RPM range. Also, saying you have a jet kit and listing the number for your main jet are meaningless unless you provide the brand name of the kit.

[THE BIG SITT]

Loss of power means that there is a very significant hesitation in that RPM range. I have to use more clutch to get the bike moving. As far as my jets, I had a DynoJet stage two kit, but it didn't have the right mains, so I replaced the mains with Keihin jets.

[94fiveohvert]

Originally Posted by THE BIG SITT

NEEDLE AND CLIP POSITION: 4th

You said you had shimmed the needles. does this mean you have 4 shims under each needle or what?

[94fiveohvert]

Also helps to know what air temps we are talking about.

[choneofakind]

if it's sputtering at low RPM's and you don't know if it's rich or lean, do an experiment. adjust it 1/4 turn out and test it again by getting it fully warmed up and going for a cruise at a low RPM in 5th or 6th, and see how it feels by just keeping a steady speed with a small throttle opening. if it surges, it's lean. If it bogs, it's rich. repeat this until you have a nice smooth low rpm cruise. only diagnose the idle mix when the bike is fully warmed up.

Jetting is trial and error. make sure to only change one variable at a time and go with what works best. Without riding it and tinkering with it, none of us can really give a definite answer.

however, using the jetting database to find someone with a similar setup and elevation as you, 2.75 turns out might be a good place to start at.

[Nemesis]

I don't have Dynojet needles in mine but know of others who do and I believe 110 is way too high.

[ForceofWill]

Originally Posted by Nemesis

I don't have Dynojet needles in mine but know of others who do and I believe 110 is way too high.

Yeah, going off what I've read, just a slip on and filter 110 dyno seems really high. I'm at a 108 with a full exhaust, filter and kleen air removed.

[THE BIG SITT]

Originally Posted by 94fiveohvert

You said you had shimmed the needles. does this mean you have 4 shims under each needle or what?

I have those "e-clip" things, so the clip is in the 4th position with three washers on top

Originally Posted by 94fiveohvert

Also helps to know what air temps we are talking about.

Roughly 50F

Originally Posted by ForceofWill

Yeah, going off what I've read, just a slip on and filter 110 dyno seems really high. I'm at a 108 with a full exhaust, filter and kleen air removed.

Hmmm… but would the main jet even have anything to do with this issue?

[ForceofWill]

I'm not sure just how rich it's making it. Normally I wouldn't think so, but if it's a lot bigger than you need making it that rich

[94fiveohvert]

pull those washers out... you don't need them with a jet kit, that's why the needle has a e clip. so you can adjust it.

[94fiveohvert]

nvm apparently it's to weight the needle? never heard of that with any of my offroad stuff. but anyways, have you checked out this thread? http://www.ninjette.org/forums/showt...eedle+position

[Boosted139]

Originally Posted by 94fiveohvert

nvm apparently it's to weight the needle? never heard of that with any of my offroad stuff. but anyways, have you checked out this thread? http://www.ninjette.org/forums/showt...eedle+position

I've had no problems with my needles without washers, although I'm on the third clip.

[94fiveohvert]

Originally Posted by Boosted139

I've had no problems with my needles without washers, although I'm on the third clip.

okay, didn't sound right to me. Though i haven't messed with any of the carb settings on my 250 yet. had multiple 4 wheelers and dirtbikes and none of them had to have weighted needles.

[THE BIG SITT]

I didn't mention this earlier, but I tried running the needle in the third position before trying the 4th position...

[94fiveohvert]

personally i think without having a full system your'e going to have problems. i'm still confused as to why you went with a stage 2 dynojet kit with only pod filters. Do you still have the factory pilot jet installed?

[choneofakind]

only difference between the stages is the range of the jets that come in the kits.

[Felipe the Ant]

Dynojet 110s!?! That's huge. I run 106s haha, or maybe they're 108s O.o

Anywho, you removed the airbox I'm assuming, that's why you're gutless below 3k. Try 106 jets or even 104s, clip in the 3rd position. Personally I have a clip with 2 washers on top and then another clip for a little more weight and easy washer storage but you can do whatever. If the low end still feels gutless put a washer under the clip leaving it in the 3rd position or move the clip itself down a notch. If you put a washer under the clip it's like moving it half a notch

[THE BIG SITT]

Originally Posted by 94fiveohvert

personally i think without having a full system your'e going to have problems. i'm still confused as to why you went with a stage 2 dynojet kit with only pod filters. Do you still have the factory pilot jet installed?

I went with the stage two kit because the guy who sold me the bike threw it in for free. When I realized the jets in the kit weren't big enough, I went to the shop and bought some bigger jets. So the needles are DynoJet, but nothing else it.

Its probably worth noting that I plan on purchasing and installing an full exhaust before next season… should I just wait till then and see how the bike runs then?

[THE BIG SITT]

Originally Posted by Felipe the Ant

Dynojet 110s!?! That's huge. I run 106s haha, or maybe they're 108s O.o

Anywho, you removed the airbox I'm assuming, that's why you're gutless below 3k. Try 106 jets or even 104s, clip in the 3rd position. Personally I have a clip with 2 washers on top and then another clip for a little more weight and easy washer storage but you can do whatever. If the low end still feels gutless put a washer under the clip leaving it in the 3rd position or move the clip itself down a notch. If you put a washer under the clip it's like moving it half a notch

But I thought the mains had nothing to do with the power down low...

[Felipe the Ant]

Originally Posted by THE BIG SITT

But I thought the mains had nothing to do with the power down low...

Only slightly but the ones you have in there are huge, you must get some serious bogging at WOT

[choneofakind]

Originally Posted by THE BIG SITT

But I thought the mains had nothing to do with the power down low...

for all intents and purposes, that is correct, but seriously how does that thing ride at WOT above 10k?? DJ 110's are GIGANTIC! I've seen guys running OEM 110's, and those are like 3 sizes smaller than DJ110's

[Boosted139]

What brand are your jets? I'm so lost

[THE BIG SITT]

Now I'm lost too… I have KEIHIN 110s. I have the DJ needles in and KEIHIN jets. But you guys are telling me that 110s from different brands may be different sizes???

[Boosted139]

Yes. So a Keihin #110 is equal to a Dynojet #106. So for your main jet size that should be fine. Could you drop one size? Perhaps, but I don't think that's your problem. Now when you say you are losing power down low, are you cruising at low rpms and then going WOT? You should really tune your top end, then middle then low for best results.

The main jet doesn't really do anything until you have the throttle open 1/8th or more. Before then it uses the pilot jets which are changing with the idle mixture screw on the carb.

[THE BIG SITT]

Originally Posted by Boosted139

Yes. So a Keihin #110 is equal to a Dynojet #106. So for your main jet size that should be fine. Could you drop one size? Perhaps, but I don't think that's your problem. Now when you say you are losing power down low, are you cruising at low rpms and then going WOT? You should really tune your top end, then middle then low for best results.

The main jet doesn't really do anything until you have the throttle open 1/8th or more. Before then it uses the pilot jets which are changing with the idle mixture screw on the carb.

By a loss of power, I mean the bike is completely stopped and when I start moving, there is a significant loss of power until i hit a certain point, when the bike takes off as it should. I have ridden it quite a few times with it acting like this, and I simply use more clutch and throttle to get past the dead zone (idle-roughly 3000RMPs).

[greg737]

By a loss of power, I mean the bike is completely stopped and when I start moving, there is a significant loss of power until i hit a certain point, when the bike takes off as it should. I have ridden it quite a few times with it acting like this, and I simply use more clutch and throttle to get past the dead zone (idle-roughly 3000RMPs).

This description sounds like it's too rich. Is it stinky? Have a friend stand on the side of your street and do a couple of ride-by idle to 4000 rpm accelerations. If the exhaust smells strongly of unburnt gas, you're too rich. It'll be pretty obvious.

Here's a reference for the Jet sizes: http://faq.ninja250.org/wiki/Dynojet...zes_conversion

[Boosted139]

I'm rarely under 3k RPMs, but you could try lowering the needle to lean it out a bit.

[THE BIG SITT]

Yeah I started at clip position 3, rode it, changed to 4, then never did anything else… I'm gonna try position two and see how that works.

[Felipe the Ant]

Originally Posted by THE BIG SITT

Now I'm lost too… I have KEIHIN 110s. I have the DJ needles in and KEIHIN jets. But you guys are telling me that 110s from different brands may be different sizes???

Oh sorry, I read through quick.

Another thing before you jump into the needles, a quick blip of the throttle at idle can usually help tell you if you got the idle mix right or not. If you blip it and it the needle hangs above idle on the tach and then falls to idle you're lean, and if it sinks like a rock and falls below idle and then back up it's rich.

Also if the sync is off it could cause issues

[alex.s]

have you checked your exhaust bearing fluid?

[THE BIG SITT]

Originally Posted by alex.s

have you checked your exhaust bearing fluid?

Is that simular to blinker fluid?

blinkerfluid.jpg

[zzrguy]

You loose low range because you don't have the airbox to create pressure.
I know this is a old post just thought I'd inform you why

[alex.s]

Originally Posted by zzrguy

You loose low range because you don't have the airbox to create pressure.
I know this is a old post just thought I'd inform you why

can you explain that please? why? is it the lack of venturis? if you had straight venturis with no filters, would you still get a low-end loss? seems to me like its more likely caused by not changing the pilot system.

[zzrguy]

changing the pilots will help! alot of people upgrade from the 38 to the 40. but youll still get a little loss from the airbox. I dont have an exact reason why all i know is something to do with the pressure of the airbox. Ill get back to you on that.