Help me! (Carbs)

[BlownWideOpen]

Hey all,

Re-jet my bike the other night.

2008 Ninja 250
Factory Pro Stage 3
110 Main jet
40 Pilot
4 washers under each needle

Pod filter
Stock header
Akrapovic slip on

Bike has a tough time starting, will come to life and then quickly die out (can't hold an idle)

After placing the bike on "prime" the bike starts and runs pretty well. If I rev it, the bike will hang a bit, drop under idle and then dies.

Idle screws are out 2 turns, I think.

What's going on? I've read the symptom could be running lean. Not sure where to start.

[alex.s]

do a plug check

[sharky nrk]

Not enough information to say for sure, but I would imagine lean would likely not be the issue with 4 washers under the needle and a 40 pilot. In theory more likely rich than lean.

[alex.s]

check the vacuum line going to the petcock. also check for general vacuum leak.

[csmith12]

Originally Posted by sharky nrk

Not enough information to say for sure, but I would imagine lean would likely not be the issue with 4 washers under the needle and a 40 pilot. In theory more likely rich than lean.

I am thinking the same thing with 110's and 4 washers. Dat's alota gas.

[alex.s]

"After placing the bike on "prime" the bike starts and runs pretty well. If I rev it, the bike will hang a bit, drop under idle and then dies."

this is the part that puzzles me. normally i would think yeah just bad jetting but this isn't right. i think he isnt getting full vacuum to the petcock to open it properly.

[BlownWideOpen]

I will check the vacuum. If it helps, when the bike does hold an idle on prime, I take it off prime and the bike will surge and make a hissing noise (maybe the vac line you mentioned). Also, when I choke the bike, the revs don't increase like it used to. Not sure if that means anything, or not.

[sharky nrk]

Originally Posted by BlownWideOpen

I will check the vacuum. If it helps, when the bike does hold an idle on prime, I take it off prime and the bike will surge and make a hissing noise (maybe the vac line you mentioned). Also, when I choke the bike, the revs don't increase like it used to. Not sure if that means anything, or not.

lack of rev rise would make me think rich still, but that hissing and junk definitely points to something else too

[alex.s]

sounds too rich plus vacuum leak

[subxero]

don't the factory pro needles have clips?

[sharky nrk]

Originally Posted by subxero

don't the factory pro needles have clips?

yes they do, I was confused about that as well.

[subxero]

Other than the needle setting which again I don't quite get because the FP needles have clips you should be fine as far as your jetting setup, nothing stands out as being so far off that it would cause crazy problems.

Like others have said, go over all the various vacuum lines ect... check that you put everything back together correctly in the carb particularly the top of the carb.

there is something else going on.

[alex.s]

could it be possible that with a much more flowing intake (pods) and a stock header still holding up most the flow that simply the configuration itself has screwed your vacuum setup? all the vacuum is escaping from the intake which can't flow any extra through the engine because of the header restriction? spitballing.

[Ghostt]

Where do I start...... Jets, shims, pod filters, petcock....... I'm gonna sit this out, clearly he's listening to the wrong people in the first place

[BlownWideOpen]

Originally Posted by subxero

don't the factory pro needles have clips?

I didn't use the FP needles, I stuck with the stock ones... Is it necessary to use the FP ones? Thanks in advance

[BlownWideOpen]

Originally Posted by Ghostt

Where do I start...... Jets, shims, pod filters, petcock....... I'm gonna sit this out, clearly he's listening to the wrong people in the first place

Pretty unnecessary comment, not sure what you were trying to achieve with that post.

Anyways...

Haven't had time to check on the bike lately, I've been busy and will be for a little while. So I will report back with my findings, once my needle question is answered.

[jkv45]

Originally Posted by BlownWideOpen

I didn't use the FP needles, I stuck with the stock ones... Is it necessary to use the FP ones? Thanks in advance

I would. I'm assuming they have a different taper (maybe length too) which would give improved metering over stock.

Put the clip in the middle and give it a try. 4 shims on the stock needle is probably too much with the main you are using.

[BlownWideOpen]

Originally Posted by jkv45

I would. I'm assuming they have a different taper (maybe length too) which would give improved metering over stock.

Put the clip in the middle and give it a try. 4 shims on the stock needle is probably too much with the main you are using.

I will give that a shot. So, FP needles with the clip in the middle and no shims. Got ya. Thank you!

[subxero]

yeah definitely use the needles, that is pretty much what you are paying for with the kit, you can get jets for $5 a pop if you know what you need.

Like Jkv said, put the clip in the middle to start and go from there.

I typically put some shims on top of the clip to help weigh it down and then another clip above the shims to keep them in place better. just my preference. Also you can use a shim under the clip to raise the needle a little bit when you are fine tuning, it will be less of a change than moving the clip a full position.

My clip is in the middle ish give or take a shim.

Before I got my FP kit, I had the OEM needles shimmed to probably 4 or 5 washers and my bike ran decent enough like that but if your washer/shims are on the thicker side it could be a lot, the stock needles are not very long

check out this post and more posts in the thread.

https://www.ninjette.org/forums/show...&postcount=109

Still kinda think you have other problems.

edit: figured I'd mention that from that linked post I have dropped a main jet size and dropped the needles, clip is more in the middle now.

[BlownWideOpen]

Originally Posted by subxero

yeah definitely use the needles, that is pretty much what you are paying for with the kit, you can get jets for $5 a pop if you know what you need.

Like Jkv said, put the clip in the middle to start and go from there.

I typically put some shims on top of the clip to help weigh it down and then another clip above the shims to keep them in place better. just my preference. Also you can use a shim under the clip to raise the needle a little bit when you are fine tuning, it will be less of a change than moving the clip a full position.

My clip is in the middle ish give or take a shim.

Before I got my FP kit, I had the OEM needles shimmed to probably 4 or 5 washers and my bike ran decent enough like that but if your washer/shims are on the thicker side it could be a lot, the stock needles are not very long

check out this post and more posts in the thread.

https://www.ninjette.org/forums/show...&postcount=109

Still kinda think you have other problems.

The shims I used are the ones that came with the FP kit, so not sure where they fall on the thickness scale. Says #4 if that means anything. I'll do what you suggested.

[alex.s]

Originally Posted by BlownWideOpen

The shims I used are the ones that came with the FP kit, so not sure where they fall on the thickness scale. Says #4 if that means anything. I'll do what you suggested.

the factory pro needle has a clip that you can move up and down on the needle. you do not shim it. some of them have two clips that surround a washer. you do not add extra shims under the clip.

[subxero]

Originally Posted by BlownWideOpen

The shims I used are the ones that came with the FP kit, so not sure where they fall on the thickness scale. Says #4 if that means anything. I'll do what you suggested.

the shims in the kit are very thin, they should be visible in the picture in the post I linked, They would be the shims on the FP needle and then the washer/shims on the OEM needle are more typical #4 washers you get from a hobby shop.

[alex.s]

Originally Posted by Ghostt

Where do I start...... Jets, shims, pod filters, petcock....... I'm gonna sit this out, clearly he's listening to the wrong people in the first place

nobody likes an asshole pointing out problems and offering no help whatsoever. your holier-than-thou attitude suggests you know precisely the problem but your dickish behavior is keeping you from actually helping someone with a problem. nobody likes posts like this and they quickly grow distaste for you as a poster when you post things like this.

[BlownWideOpen]

Originally Posted by subxero

the shims in the kit are very thin, they should be visible in the picture in the post I linked, They would be the shims on the FP needle and then the washer/shims on the OEM needle are more typical #4 washers you get from a hobby shop.

So, I made some time and got in the garage (even though it's -30°C) swapped out the needleswith the shim in the #3 (middle) pposition and sammiched a couple washers on top of it. Needless to say, it runs much better now. I the garage was warm enough to where starting it wouldn't be too bad. The choke is a little sticky now though. I think the fact that it's cold and hasn't been lubed in a while doesn't help. Once it's a bit warmer it will be easier to tell. Had to cut it short 'cause I have to pack for Army training this weekend. But thank you for your help.

[BlownWideOpen]

Originally Posted by alex.s

nobody likes an asshole pointing out problems and offering no help whatsoever. your holier-than-thou attitude suggests you know precisely the problem but your dickish behavior is keeping you from actually helping someone with a problem. nobody likes posts like this and they quickly grow distaste for you as a poster when you post things like this.

I find this post helpful. Thank you as well for all your input so far. I appreciate your help, even if you hate Mustang's.

[Ghostt]

Originally Posted by alex.s

nobody likes an asshole pointing out problems and offering no help whatsoever. your holier-than-thou attitude suggests you know precisely the problem but your dickish behavior is keeping you from actually helping someone with a problem. nobody likes posts like this and they quickly grow distaste for you as a poster when you post things like this.

Yes I'm an asshole, but my point of my post is he has multiple issues, and it would require multiple fixes, he's done too much at one time, instead of one thing at a time. Do I need to point out that pod filters and CV carburetors don't work??? I'm sure you realized this too.

I ment no offense by my post, just trying to be funny, and I ment no disrespect to the O.P., or any other forum members.


So to un-asshole myself,

I personally would go back to the OEM airbox, return the carburetors as well to OEM specifications, get bike running properly, then start making the changes one at a time, tune the idle mixture screws return to OEM jet size a good starting point is 3 turns out, test ride, make adjustments til your happy, try only main jets first, up one size from stock, no shims, test ride note performance, better, same, worse, etc.., try shims start with just 2, test ride note performance, better, same, worse, etc.., tune to the bike's liking.

Tuning carburetors are easy, but it's time consuming, but worth it in the end.

Once again my apologies.

[alex.s]

Originally Posted by Ghostt

Do I need to point out that pod filters and CV carburetors don't work???

forgive my lack of knowledge, but i thought fancy newer pod filters like the one KN makes for this bike have built in venturies/runners. so if its got a runner, why wouldn't it work with a cv carb with correct tuning? its a dohc with a venturi... what difference would the type of filter make?

just a side note, theres probably close to 100 ninja 250s on this website that have pod filters and full exhaust that dyno pretty high. higher than with the stock airbox.

[Ghostt]

Originally Posted by alex.s

forgive my lack of knowledge, but i thought fancy newer pod filters like the one KN makes for this bike have built in venturies/runners. so if its got a runner, why wouldn't it work with a cv carb with correct tuning? its a dohc with a venturi... what difference would the type of filter make?

just a side note, theres probably close to 100 ninja 250s on this website that have pod filters and full exhaust that dyno pretty high. higher than with the stock airbox.

I don't know about the K&N pods, but I know from pods. I'm not saying that they don't work, they can, but requires much tuning, and personally not worth the time, when the OEM airbox and K&N replacement filter will do nicely.

Here I'd my explanation from another posting,

I would highly recommend that you DO NOT REMOVE THE AIR BOX, the carburetors on the bike are CV type and need the box to function properly, buy a K&N that fits the OEM airbox(K&N KA-2508 Kawasaki High Performance Replacement Air Filter by K&N* *Amazon.com: K&N KA-2508 Kawasaki High Performance Replacement Air Filter: Automotive* ) that's the short version.

Long boring but important answer, CV carbs stands for "constant velocity". The function of the carbs is dependent on having a calm reservoir (airbox) from which to intake air at said constant velocity. Pods draw from the turbulent, unpredictable air swirling past them as you ride, which is anything but constant. Other carbs work fine with pods. CV's = no bueno, save yourself the headaches.

Now onto jetting, first you need to tune the idle mixture screws first, I recommend 3 full turns out from bottom as a good starting point, then fine tune them afterwards. As far as buying a jet kit, I personally don't have one on either my 250, or 500 ninjas. I did got up one size on my main jets, due to they are lean from the factory, and shimmed the main needles with a small washer.

[alex.s]

i was trying to find more info, here's what i've found so far.

from wiki:

Fixed-Venturi
in which the varying air velocity in the Venturi alters the fuel flow; this architecture is employed in most carburetors found on cars.
Variable-Venturi
in which the fuel jet opening is varied by the slide (which simultaneously alters air flow). In "constant depression" carburetors, this is done by a vacuum operated piston connected to a tapered needle which slides inside the fuel jet. A simpler version exists, most commonly found on small motorcycles and dirt bikes, where the slide and needle is directly controlled by the throttle position. ... These carburetors are also referred to as "constant velocity" or "constant vacuum" carburetors. An interesting variation was Ford's VV (Variable Venturi) carburetor, which was essentially a fixed Venturi carburetor with one side of the Venturi hinged and movable to give a narrow throat at low rpm and a wider throat at high rpm. This was designed to provide good mixing and airflow over a range of engine speeds, though the VV carburetor proved problematic in service.

here's another wiki article from a weird site:

The CVK40 is technically a bleed type carb, with a variable venturi that's controlled by constant velocity (CV). It's also known as Constant Depression or Constant Vacuum. ... The area of lowest pressure is just past the narrowest point and is called the depression. ... A variable venturi varies the venturi diameter at the depression by raising or lowering an obstruction. This obstruction is called a slide. On a CV the slide is called a piston or diaphragm valve.

[Ghostt]

Originally Posted by alex.s

i was trying to find more info, here's what i've found so far.

from wiki:


here's another wiki article from a weird site:

What kind of air filtration system do you personally run?

[alex.s]

rules say stock airbox

[Ghostt]

Originally Posted by alex.s

rules say stock airbox

Okay, but have you tried pods, on any bike you have owned before?

[alex.s]

yes

[Ghostt]

You know what? never mind
First rounds on me Alex

[subxero]

Originally Posted by Ghostt

I don't know about the K&N pods, but I know from pods. I'm not saying that they don't work, they can, but requires much tuning, and personally not worth the time, when the OEM airbox and K&N replacement filter will do nicely.
Here I'd my explanation from another posting,

clearly you have never done carb tuning on a new gen N250 with air box removed and pods It's like.... walking on sunshine compared to stock
Although getting that pesky air box out can be a chore.

[BlownWideOpen]

Key word there is "personally". So please, don't speak negatively towards others that choose to do something you personally wouldn't do. I had the stock airbox with a K&N replacement, that's one of the first things I did. But I wanted more.

So, it's running great now. Just have to get on the butt dyno.

[jkv45]

Chances are you will need to make fine adjustments to the idle mixture screws to get it to idle evenly and transition to midrange smoothly. Syncing the carbs is also a good idea before doing too much fine-tuning.

As temps drop a carbed engine will run leaner, so the correct adjustments for cold weather won't be the correct adjustments when the temps are 50 degrees warmer or whatever.

Summer-blend gas won't vaporize in cold weather, so make sure the gas is fresh.

Gas with ethanol will also make a carbed engine run leaner than gas without.

Just one of the many reasons to avoid it...

[webfoot]

I went with the dyno jet stage 3 kit as to their specs and it worked perfect. Hope you got yours figured out bro

[webfoot]

I put the K&N filters on, what a diff, but yes, that friggin airbox removal took more time than putting in the stage 3 kit, slip on filters on, sidecovers, seat and tank on. Like to meet and greet the moron that designed the stock airbox. Had to have 2 beer breaks while removing it. HATE that air box. LOL