How to derestrict a stock Tomos A55 airbox

LanceCampeau /
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Sorry, no photos/video for this one as I wrote this tutorial a long time ago... just follow the steps to derestrict you stock Tomos A55 airbox and get your engine breathing a bit better (untill you can do some _real_ upgrades ;)

It's not hard to modify the stock airbox for an A55 engine...

#1 - remove the airbox from your ped

#2 - open up the airbox by removing the 3 retaining screws.

#3 - remove the internal foam filter and the plastic frame that holds it in place.

#4 - Inside one half of the airbox, you will see a 90 degree metal nozzle attached to a small rubber pipe. This is 1 of 2 items you will be modifying.

#5 - Remove the whole rubber pipe/metal nozzle/flange assembly from the airbox. It's all one piece at this point.

#6 - cut the hose/nozzle away from the flange that connects to the airbox.

#7 - At this point, you should have 2 pieces. a rubber pipe with the metal nozzle... and the flange that attaches the airbox to the carb.

#8 - you won't need the pipe anymore or metal nozzle anymore, put it aside.

#9 - now use an exacto knife to remove bits of rubber from the hole in the rubber flange. You want to widen this as much as possible... but be careful not to overdo it. After you widen the hole, re-attach the flange to the airbox. At this point, you are finished with this half of the airbox, you can put it aside.

#10 - the next part involves the other half of the airbox... You will want to drill some holes to increase air flow. It's important to drill them on the back or the bottom of the airbox to prevent rainwater from entering. I drilled 14 holes, each are 1/4" in diameter. This has proved to be enough to get the Engine breathing freely.


#11 - put the airbox back together and then put it aside while you upjet your carb. After upjetting, put the airbox back on the bike. Your done.

You will have to experiment with the jets... I have the following... 56,58,60,62,64,66,68

56 is too small (run the risk of damaging engine)

68 is way to big (poor performance)

60 worked okay, it was fast but 62 provides the best balance for my 50cc setup. You will have to experiment.

I'm 250 LBS and I carry 20 LBS of gear. The bike also weighs 145 LBS... That's a lot of weight to haul around (hills aren't so fun). Your needs may be very different... try a smaller rear sprocket for more top end if your overall load is lighter...

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