TOPIC:

this is what I was talking about when I said to modify the airbox
Written by philcsand
Wednesday, 23 November 2005

If you decide that the idea of pods is too scary, then you are stuck with your factory airbox, and it's constricted intake... or are you...?






As some people have heard, I have developed a modification to the stock airbox that greatly increases it's ability to pass air, while eliminating the turbulence that pods introduce.






This method was designed an airbox for a 750, that uses a round filter. (like a large soda can shape), but can probably be modified to work with other styles.






First, it is important to pull the airbox out, and take stock of what you have. On the airbox, you have 3 main parts that we will be dealing with. 1st is the retaining ring that you unscrew to access the air filter. The modification to this part is easy, just use a hacksaw to cut the perforated tube off even with the threaded section of the retainer. (You want about ½ to 1 inch of the tube still there, this will keep the filter in it's proper place.)






The second part we are going to deal with is what I call the pedestal. This is the part of the airbox that the filter element actually sits on. It will pull straight out of the airbox without much trouble. All you need to do with the pedestal is throw it away. Lastly, you are left with the airbox. Place it aside for the time being, and go to the hardware store. You want to go to the plumbing section, and look at the black PVC pipe section. What you want is a step-down adapter that has an ID on the smaller side of 2 inches, and an ID on the larger side slightly smaller than the OD of the filter. It should also be taller than the pedestal you removed. When you get it home, you will need to do a few fun things. First, use a 2” hole saw to cut a hole in the bottom of the airbox. Use the hole that the pedestal was mounted in as your center point. Next, use a sanding drum, or cutting tool on a dremel to route out the inside of the larger part of the PVC adapter so that the air filter can fit snugly into the adapter. You will want to trim it down to the point where it comes up about a half inch on the outside of the filter. Next, take the filter, while it is stuck in the adapter, and place it into the airbox. Measure how far above the top of the threaded section, and take note. Pull the filter and adapter out, and then cut that amount off of the small side of the adapter. Re-fit the adapter and filter, and make sure the filter is flush with the top of the airbox. Pull the adapter and filter out again, and then snag some contact cement. I used one that was billed as oil and gasoline resistant. (Important on an engine) Use the contact cement to glue the adapter in place directly over the hole you cut in the bottom of the airbox. (It is a good idea to use heavy grit sandpaper to rough up the airbox plastic to ensure a good bond.) I used the filter and retaining ring to hold the adapter in place while it was curing. The final step is to use a rasp to blend the airbox plastic into the adapter, so there is a smooth transition.






To top it all off, buy a foam / oil filter and slap it in place. With this setup your engine will be able to pull in all of the air that it can possibly want.

Scott

Post edited by: 77KZ650, at: 2006/10/21 19:12

Have those of you who've modified the stock airbox noticed any definite improvement in power? Needed to rejet?

Post edited by: glenncarpenter, at: 2006/10/21 20:54

Rubberlips,

Revs staying up like you're describing is a dead giveaway of leanness on the bottom. You need to go up a pilot jet size or turn the fuel screws out. If the fuel screws are more than three or four turns out, they're basically maxed and you need a bigger pilot jet.

The pilot jet and fuel screws both affect the low end jetting, but the idle screw has the largest effect right at idle, whereas the pilot jet continues to have a significant effect up to 1/8 throttle or so. Having the mixture screws between 1 turn out and 4 turns out or so is a good indication as to whether you are running the right pilot jet.

My guess is you'll end up with a larger pilot jet, but try the idle mixture screws first as that will give you an easy indication as to whether you're on the right track.

thanks alot .ill try these suggestions and see what happens.

I have had pod filters on by KZ650 for over 20 years and never experienced any of the problems I read here. My bike starts esily, idles great pull shard and I never noticed any bogging on windy days. I have ridden it in hard rain and never experienced wet filters.
As far as jetting goes I have a 118 main, 17.5 pilot with the mixture screw 1 1/2 turns out, needle in the second slot from bottom.

I should say I've run pod filters in the past with no problems as well. I suspect it's mainly in the case of leanness that sidewinds will cause a problem. I imagine they have a small affect on intake pressure, enough to give an already-lean carb problems but not one that is jetted properly.

I should also say that I've never known rain to be a problem with any pod setup at all.

My real problems with pod setups are the noise, and the fact that an airbox is indeed part of the intake tuning, so that you are almost guaranteed to lose power with pods at some point in the rpm range. It may not be enough to matter, and the resulting extra progressiveness of the powerband may actually make the bike feel faster, but the dyno will always show there to be a tradeoff with pods.

thanks,i dont know whats wrong iguess ill have to change the pilot and needle cause i just cant get these carbs right ,i thought i had it ,ideling great,seemed to be running good,carbs all reading 20 to 22.then it would just rev right up.i gotta walk away from it for a while.thanks again.

thanks guys ,it's definitely the pilot jets.i remembered i had a second set of the same size pilot jets that are in the carbs.so being impatient i drilled a o.80mm hole through the second set just to see what happened. well it idled allright and no problem with throttle id rev it up and it came right back to idle good.so ill be sending away for new pilot jets.thanks for advice.

The motorcycle company's in the 60's and all through the 70's did not design the airbox to be part of the tuning of the bikes. This practice did not start until the early 80's. Ever notice all the race bikes in the 70's had pod filters? If removing the stock airbox lost power then I am sure all the pro tuners for the race bikes would have left them on.
The air boxes on most early Jap bikes were simply to filter the air nothing else.

baldy110 wrote:

I have had pod filters on by KZ650 for over 20 years and never experienced any of the problems I read here. My bike starts esily, idles great pull shard and I never noticed any bogging on windy days. I have ridden it in hard rain and never experienced wet filters.
As far as jetting goes I have a 118 main, 17.5 pilot with the mixture screw 1 1/2 turns out, needle in the second slot from bottom.

i have sent away for the jet's you mentioned above and a couple of other size's too while i was at it .i am very confused as to why the bike is running lean the only modification's i made were to add the dyna s ignition and green coils but since they went on i cant seem to sync the carbs ,now the bike wont even start no spark from coils.anyway ive decided if for no other reason other than removing and installing the carb's im putting on the pod's.thank's again

Hi rubberlips, hope you get the bike going. I inherited K&N pods on my bike and like baldy have never had a problem with them and they are great for easy removal of the carbs. However I just cant see them working long term in Irish weather.

Good Luck.

hi,i dont usually ride when it's raining, at least not on purpose anyway.but these carb's have been on and off more times than a whore's knickers in the last 2 week's.so i will give the pod's a shot anyway.thank's.