Carb jetting?

[sephia]

i have a newbie question...if i get a new slip on can, will i need to get a jet kit?

[Super Sneaky Steve]

Ask the manufacturer of the can. Most do not require a rejet but I would at least adjust the pilot screw.

Do you know how to do this?

[MotoGPFan26]

I for one don't even know what a pilot screw is....and now I'm interested.

Steve...you need to go make another video...

[Super Sneaky Steve]

I have pictures from my last bike of my carbs, but my current bike has none.

I think the hardest part will be reaching the inner carbs and getting them all even. I believe Honda makes a tool to reach them.

Anyway, I'll post up after work.

[rndthought]

i have a newbie question...if i get a new slip on can, will i need to get a jet kit?
Think general consensus is that, just the slip-on no re-jet needed. If you also go to a free flow air filter like a K&N then you'll need to re-jet as she will start to run too far on the lean side.

[Super Sneaky Steve]

Here is a picture of the carbs on my EX500. As you can see they are easy to get to. Not so much on the 599.

The blue arrow is pointing to my idle adjustment knob. With a warm motor you can twist this to be within spec of your owners manual. For my little ninja that was 1,300 RPM.

The red arrows point to the pilot screws. Mine were capped from the factory to keep kids like me from messing with it. They can be removed a few ways. You can use a dremel tool, or you can poke a hole in it with a nail and hammer, then screw a wood screw into it, then pull the screw which will pull out the cap with it.

Once the caps are removed now you can adjust them. It's very easy to do. First tighten the screws in gently untill they seat (clockwise) Then back them out 2 full turns. This is a good place to start. Be sure to turn each screw on each carb equally.

To help me count turns I put a piece of tape on my little screw driver, then drew a dot on it. This let me count a rotation every time I saw the dot. Using a small mirror helps see what you're doing as well.

Back to the screwing! Now that you have a starting point you must find the lean and rich threshold. Add the two and divide by two to find your optimum spot.

To find the lean threshold start to turn the screws in 1/2 turn at a time. When the motor starts to idle rough you know that you've found the lean lean limit. Lets say it's 1 turn out.

Now go back to your starting point, which was 2 turns out and find the rich limit. Start to back the screws out 1/2 turn at a time untill it idles rough. This is your rich limit. Lets say that it's 5 turns out.

Now, take the lean limit (1 turn) add it to the rich limit (5 turns) which equals 6 turns and divide by two which is 3 turns out. This would be the best for my twin, but! you have a 4 cyl motor! This means that the inner two cylinders should be about 1/2 turn richer than the outer two.

The reason is that the inner two cylinders get hotter than the outer two. Fuel not only provides power, but it also helps to cool the motor.


http://i4.photobucket.com/albums/y123/ex500/SSS/carbwitharrows.jpg

[rndthought]

Steve, is there any way to tell if you've reached the limit of the "rich" side of the adjustment screw?

Cause if the breathing gets opened up enough, you'll be beyond the range of the standard jets/needles. Not sure if this is possible with just a slip-on and an air filter but there are jet kits for the bike so I'm sure it is possible some how... or do the new jets/needles just play with the power curve by profiling the needles different?

[Super Sneaky Steve]

When you reach the rich side of the adjustment you'll have poor ideling. It will stumble around and eventually stall.

The pilot screw will effect the bike mostly from the lower half of the throttle. When you go half way open to WOT (Wide Open Throttle) then you are working mostly with your main jet.

If you want to save some money you can spend $6 on a larger main jet and you'll have 95% of what the jet kit will do. The jet kit is usually tested on the bike that it's made for it, so that $100 you pay is really for the dyno time.

I'm not an expert on this so if anyone else wants to jump in on this subject please do. I've just tinkered around a lot and asked a lot of questions, just like you guys are doing now.

[Super Sneaky Steve]

I think I misunderstood your question. I think what you're saying is can the motor be leaned out so much that you'll need a Jet Kit.

It's possible. What you need to do is look for flat spots in the powerband. Most likely it will be when you're comming on to the main jet somewhere in the middle to high end. For that you'll need a new main jet.

I have a few Jet Kits laying around. I'll make a video showing all the parts and the instructions that come in the box.

[rndthought]

... think what you're saying is can the motor be leaned out so much that you'll need a Jet Kit...
:thumbsup
This is black magic to me... :wink:

[mechanic77]

what i dont get is from the factory the inner two carbs have bigger jets but when you do a DJ kit they insist that you dont need bigger and recommend all the same and also the same adjustment on the screws too?? I dunno who to believe I just adjust till she runs good ,,, ride for a bit then check my plugs and make further adjustments if neaded based off the plug readings

[Super Sneaky Steve]

The jet kit in my ninja looked smaller than the original main jets. I think it's because the needle is thiner with the jet kit.

The needle in the kit is also adjustable with a clip. I'll make a video of this friday. I promise :wink:

[sephia]

WOW thanks for all the post with the quickness... i guess ya just slip on the can and she if she runs well or not
thanks again!

[mechanic77]

yeh mine where also smaller in my kit but plugging the air jets is why this is..... and yeh the needles are adjustable and the profile is supposed to be better then stock thus increasing throttle response

[drew]

I'm a bit of a carburetor guru, so maybe I can shed a little light...The pilot jet only supplies fuel from idle to about 1/4 throttle. The pilot screw (which may adjust air or fuel, depends on the carb, so turning it right may mean rich, or it may mean lean, left, vice versa...) only affects the same idle to 1/4 throttle. After that, fuel is metered by the needle and the needle jet (emulsion tube). The taper of the needle, the emulsion tube orifice diameter, the type of emulsion tube (primary or bleed type), and the angle of cutaway on the slide all play into part throttle fuel metering. The main jet is the last piece of the puzzle, it only affects near to wide open throttle. Often when jetting carbs for custom applications, one will leave the main jet out of the carb entirely while they fine tune the slide/needle/e-tube combo (that way it can't be of any restriction). Once the bike runs good in the midrange (it will fall flat on its face @ WOT with no main jet in there), you start trying different main jets (starting too large and working smaller) until its right. This is for custom apps- the avg. street bike will never need this much tinkering. Usually the biggest improvement will come when the jet kit is done with other mods, and I think its usually the needle that receives the most attention. The pilot shouldn't need to be altered unless you've done other mods, the needle jet or emulsion tube (whichever name you prefer) works together with the needle, so you generally only need to mess with the needle unless you are making major changes, and the slide cutaway is another whole story. Most of our bikes have CV carbs, where the slide rises due to airflow, and the throttle controls a set of butterfly valves. These type of carbs usually dont have different slides available, although I've seen some people mess with the air holes in them to make them rise faster. The other type of carb is a direct control slide carb, where there are no butterflies, and the slide is raised by the throttle cables directly. These carbs aren't as common on street bikes as they are much more "abrupt". The different jetting on the inboard carbs is probably due to those cylinders running hotter, and I'm guessing the affect of staggered jetting like that is less after you've richened the mixture up by jetting, thats why the aftermarket kits don't bother. It also may have to do with the way the factory header scavenges each cylinder, but Honda is known to design efficient exhausts, so ? If I lost anyone in there, maybe i can write up a beginners guide to carbs and start from the beginning, like, what are these infernal things, and how do I make peace with them?....... :D

[rndthought]

So let's see if I'm following you...your saying don't touch 'em. :wink:
Unless you have a reason to and you know generally what you’re doing... :D
Thank you, very nice explanation and will be curious to hear from those who do "adjustments."

Personally I’m fine with the power I have now - the only carb adjusting I’d like to make sure is proper is that the are not running too lean or too rich and are balanced… some of which I can get from the plug probably if I knew what to look for and how to get at them. (black = too rich, brown/damaged = too lean?)

Anyway, thanks again! I feel smarter already and it’s only the second day of 2007!

[drew]

if the plugs are sooty and black, too rich. Too lean and your plugs will be white, like when they were new. Too rich is always safer than too lean, which runs hotter and can burn valves, pistons, melt spark plug electrodes, etc. :shock:

[mechanic77]

LOL I hope you got the rights to be able to copy/paste that info dude :lol:\\just kidding wonderful info dude :thumbsup