should I do intake or just rejet?

[greenmachine]

So I have an 08 and I bought it with a two Bros slip on and I've realized that I'm running lean and I also think I'm due a carb cleaning and new chain. So my main question is, should I also do an intake mod before I rejet? Is it important to do so or is it just more of a jetting hassle?

Any suggestions on jet kits or intake? I know factory pro and dynojet are the 250 favorites.

Should I also synchronize my carbs?

[Ghostt]

A very loaded questions, I'm not familiar with the NewGen airbox set up.

As far as jetting goes I'd go up one size on the mains, adjust the idle mixture screws, maybe shim the main needles if needed.

But first start with a through and meticulous carburetor cleaning, and make sure all is right, make only one change at a time, be sure to set the float height as this is the most crucial and overlooked part.

Here's some how-to guides

Your initial setting should be 3 full turns out from the bottom, remember just slightly tighten them, don't go all Conan on them.



Then warm it up, slowly turn 1 side pilot screw in until the rpms drop, then back out till RPM's peak (and no further)* Twist throttle...see how it reacts...tweak to taste.
Repeat on other side... test ride. You're looking for best throttle response and transition from just cracked to 1/4 throttle opening or so.*

Thats a quickie, 10 cent tutorial on setting pilot screws.**

You can get a reasonable sync with the carbs in hand. Back the idle adjustment off to close that carb then match the second carb to it with the sync screw. You can then turn the idle adjustment up while using a thin feeler gauge (maybe .002") between the throttle plate and the throttle bore, adjust to just fit, and then check the second one and adjust to match. If you have good feel for this it will run fine once installed.*

It would do folks well to take a minute to review and understand what a sync tool does, how it works. And take another minute to look at the carb linkage and sync adjustments available to fix irregularities that might occur. It can help take some of the mystery out of this as well as stop unnecessary carb sync screwups.*

Meaning, that the carbs were right once, the butterflies were matched and it performed well, but then changed. Undecided And the problem somehow occurred in the butterfly direct shafts, or the sync screw turned or wore that pad that it rests on, or the carburetor pairing/ bridging brackets twisted in relation to each other, and enough so that the butterflies no longer operated in sync, such that performance noticeably suffered. And a fix will be accomplished by changing the butterfly position, the only thing the sync adjustment does. Hmmm. Really? Undecided*

Meanwhile, the tool measures vacuum at each individual runner. That's all it does, how it works. And vacuum is effected by a huge list of things, butterfly position being only one of them, and the only one addressed with that tool while turning those sync screws. The rest of that list includes, valve adjustment, jetting, float level, compression differences between cylinders caused by wear as well as factory CC differences in the head, intake runner, as well as flow by port variations, etc. Variations in cams, wear or factory tolerance. Then there's the potential big one, pilot jets and pilot screw mixture settings. All of those effect the vacuum and will be read by the sync tool, accurately identifyng the difference that exists, and with the only adjustment being used to "correct" the problem, move the butterfly relationship, one to the next.*

It's that clear understanding that has me of the opinion and long time practice to not touch the sync screws on a set of carbs that were right once and were never dismantled from the rack. And jet cleaning as well as float needle changing doesn't require that they be dismantled. And further, if I DID dismantle a set of carbs, I just matched the butterflies on the bench at assembly, using a feeler gauge, and then never touched them again, never gave them another thought.*

That method, properly executed, will have THAT portion of the complete equation, balanced flow to each cylinder in a multi-cylinder/ carb application due to butterfly position, satisfied entirely adequately. And in fact, it has worked for me every time I've done it on every bike (as well as individual runner/ butterfly V-8 intakes, all eight) that I've ever owned or any that I've fixed for others. And the times I fixed for others was usually after an attempt by others to sync the carbs, chasing a problem, or sometimes not even chasing a problem, but one they created wth a sync tool, chasing a problem from that list, that was never a butterfly position change problem. Those linkages are so direct and simple that they don't know how to screw themselves up. Not enough to care about.*

I'm sure this will start a lot of controversy so I won't argue it, just offering it for those who understand the whole picture that I outlined and might make good use of it. It is what I've done, on every engine I ever worked on, including blue printed racing engines as well as regular old, high mileage street stuff. I've had at least four, four cylinder bikes with over 100,000 miles that ran quite well, the whole time, and never had a carb sync performed. When they did finally get a total disassembly, this is how I set them up, on the bench. Over the years I've straightened out at least a half dozen messed up ones, probably more, and on the bench, after fixing the original problem which was fouled pilot jets.*

I only posted this because it seems like its coming up fairly often, especially with problems from a sync gone bad. One I would suggest was never a sync problem to begin with. A big or sudden change in performance is NEVER a sync problem. NEVER. Remember that. Cool If there is a problem, and you connect the gauges? YES, there will definitely be an imbalance indicated. But because that hole has a problem that is from the rest of the list. A bad plug, a plugged pilot jet, a screwed up float, a bad valve or setting, etc. Every one of them effecting the vacuum in the intake but NOT from a sudden move of a butterfly position, a sync adjustment.

Any questions please feel free to ask

[greenmachine]

Thanks for all the info! So you think I should do all that with stock intake snorkel and all?

[Ghostt]

Originally Posted by greenmachine

Thanks for all the info! So you think I should do all that with stock intake snorkel and all?

I'm not familiar with the NewGen to know, but I'm an OEM airbox kind of guy, pods are bad IMHO

Here's my 2¢

I would highly recommend that you DO NOT REMOVE THE AIR BOX, the carburetors on the bike are CV type and need to 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.

[greenmachine]

I'm looking for least hassle and least money spent so that the answer I was looking for :P keep the intake stock and clean the carbs sounds like a good first step to me, any idea what size jets I should look into? Stock is 98 and I'm looking to go 100+ correct?

[Ghostt]

One size at a time, I would advise small steps, and be sure to get OEM jets as aftermarket sizes don't follow the same sizing sometimes.

I also recommend getting a K&N drop in Air filter.

[DaBlue1]

Originally Posted by greenmachine

So I have an 08 and I bought it with a two Bros slip on and I've realized that I'm running lean and I also think I'm due a carb cleaning and new chain. So my main question is, should I also do an intake mod before I rejet? Is it important to do so or is it just more of a jetting hassle?

Any suggestions on jet kits or intake? I know factory pro and dynojet are the 250 favorites.

Should I also synchronize my carbs?

Sounds like you need a few easy Performance Tips.

[csmith12]

[alex.s]

pull the snorkel, leave the box. then rejet

[adouglas]

Every time you make a mod you need to deal with fueling to get it right again. So do all the simple mods at once. When I got an AreaP full exhaust I did the following:

- Remove snorkel
- Remove Kleen Air system (didn't get a block-off plate... just put a rubber cap over the breather and plug the remaining hoses)
- K&N filter
- Rejet

This stuff is easy, not expensive and will work great.

By the way... it's a good idea to keep what you take off for when you eventually sell the bike. It's a plus.

[DmbShn41]

Search the forums for the jetting database where other riders have posted their exact setups (exhaust type, jetting settings, etc) so that you have an idea of where to start. It helps because if you buy a Stage 2 kit, but really need a Stage 3 kit, then your the proud owner of some parts you don't need....plus it takes some of the guesswork out. Understand that someone else's exact settings won't copy to your setup and make it perfect, it will get you close. Things to consider are ambient temperature, altitude, etc.

[alex.s]

to be honest just having a slipon isn't going to change anything really

[Ghostt]

Very true Alex.s.

I personally would go up one size on the main jets, tune the idle mixture screws, then if necessary shim the main needles if needed.

The carburetor mains are on the lean side from the factory, personally save your money and don't buy a jet kit IMHO.

[DaBlue1]

Originally Posted by Ghostt

....The carburetor mains are on the lean side from the factory...

A little piece of info...

"Carbureted powersports vehicle manufacturers do not jet their carburetors perfectly, for two reasons. First, there are emissions considerations, mostly affecting the idle and midrange carburetor circuits. Consequently these circuits are jetted leaner than normal, and should be richened slightly for better performance. However, this rarely requires more than an adjustment to the idle mixture screw, and in some cases an adjusted slide needle height. Second, manufacturers ship their product to many different places across the globe. They purposely jet too rich on the main jet, the carburetor circuit that presents the most liability in terms of engine overheating. Therefore, all road-going powersports vehicles are jetted "fat" on the main jet. Contrary to what many people believe, but true nonetheless. Manufacturers do this because they cannot jet individually for each market, so they simply err on the rich side rather than the lean side, because the latter would present more problems. The fact is, engines are much more forgiving of a 3% rich condition than an equal lean condition, and just as importantly, few customers will notice a rich main jet, while nearly all will complain about a lean one."