Qt50 adjustable airbox

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want to adjust your jetting while you ride? well, here you go..


what you will need:

1. stock carb to airbox rubber grommet

2. k&n rc-2540

3. k&n aerosol recharge filter care kit

4. 1" pvc shutoff valve as pictured below, you can get them at ace hardware or most any hardware store. it should be the slip type and not threaded. the k&n filter will magically pop right in and hold tight.. perfect!

5. extra jets (larger) for tuning this thing in perfectly, i will explain later... if you know you want a 75 main jet in your carb when you are done, maybe get an 77.5, 80, 85, 90. jets


Ball valve 207 medium.jpg

slip type 1" pvc ball valve. you can paint it to your color of choice.


ok, so, now what do you do with all this stuff?

1. take your ball valve and close it all the way. drill out one side of the ball valve, so only one side of the actual ball will be controlling the air flow. you may have to dremel it out or get creative, but you get the idea. make sure you debur any flaky edges.

2. put the rubber grommet on your carb, hold the pvc valve up to the grommet, you will see we need to trim just a bit of the fat off of the grommet for the valve to push on. take this part slow as you don't want to remove too much rubber or the valve will be a loose fit and that would = order another grommet. once you have it trimmed, the valve should push on and hold snug, how fun.

3. now you have to decide what jet you would like in the carb when you're done tuning this thing in. I like to shoot for a 72.5 jet in mine as i am stock and it gives a bit more umph than a stock 70 and keeps the gas mileage high. point is, choose the jet YOU want to end up with in your carb, knowing if it's too rich or lean, you will be able to control that.

4. now that you have your jet picked out, we need to get oil on your filter. pull your carb off and throw a large jet in you carb, lets start say 1-1/2 jet sizes larger. so, if you want a 72.5 jet when you are done, throw a 87.5 jet in the carb and reassemble. put it all together, carb, ball valve and filter.

5. set your ball valve closed half way. get out your k&n oil aerosol spray. lightly mist your filter until your 1-1/2 size larger jet is 4-stoking on the top end while riding or on the stand. leave the ball valve closed half way. do not move until we are done.

6. pop the filter out, pop the pvc valve off the carb, pay attention to not bumping the valve close or open. throw an 82.5 jet in the carb or a jet that is 1 full size larger than your jet you decided on..

7. reassemble carb, ride, does it 4 stroke? is it lean? if it's lean, "baby steps" lightly mist-spray the filter until you just get it to bog on the top end.. if it is rich, continue down jetting a 1/4 size at a time. the key here is to slowly inch towards your correct jet by lightly misting the filter.. once you work your way down your jets, stop at the jet that is 1/2 size up from your selected jet. you will figure out what is going on here and how you can tune it in... trust me, this is a great addition to any moped, makes life grand.. its a little finiky to tune in, but makes life super easy when your work is done. you might not make it exactly to your jet you want, but you will get close.. dont cry.

8. once you get it right around the jet range you want, you are going to want to play with the valve setting and see what is going on, be careful of adding oil to the filter at this point (too much oil and you gotta clean the filter and start over). figure out where you need to go. i like to have it jetted perfectly when the valve is 3/4 open, but tuning it to where it is closed half way errors on the side of caution. the valve at 3/4 open is smooth and easy to work with and at 3/4 open it allows you to lean it up or richen the mix with ease while riding.

9. it's trial and error.. you want to get your jetting right when the valve is 3/4 open. baby steps oiling the filter and down jetting until you get to the correct jet size is how it is done. MIST the filter, do not SPRAY. focus.. patience

10. that was a lot of explaining for something that looks so simple. i probably confused you.

11. you will get it.


Qt50 adjustable airbox.jpg

Picture of the setup before oiling a freshly cleaned filter

MATT BODA1NZ