Wednesday, November 26, 2014

DIY Air Cleaner

This generally doesn't happen often, but its happening to me so I decided to document it. ever get a large sized carb that is so big you can’t get an air filter/cleaner for it? well, if you are in US, maybe not, but here in Malaysia, getting a Harley carb conversion isn’t as simple as running to the store to buy an air filter.

My bike is in the process of being converted to a single carb (trust me.. not easy with a dragstar), and the carb I am using is not a Harley carb but a 39mm racing carb. Here’s where the problem comes. I did  not expect a large bell mouth so there is no motorcycle shop that sells aftermarket air cleaners for it. the only ones available is from a Harley which in this case costs more than the carb I bought. So I decided to buy an air filter for a carburetted car.

What you need:
1.       Air filter kit for a carb car (preferably something small)
2.       Scrap metal strips about a foot long
3.       Screws, nuts and bolts
4.       Larger piece of scrap metal.
5.       MIG/TIG/Stick/a friend that can weld.
6.       Grinder
7.       Hose Clamp that fits your carb
8.       Drill and bits
9.       Paint

Step 1:
Know what your air filter does and what you need to do
The air filter is designed for car carbs. This means that there is an off centre hole roughly in the middle and the top cover is held down by a bolt that bolts to the inside of the carb. This means that the carb can’t hold itself and you will need to fabricate several things
1.       A mounting point for bolting it to the carb
2.       A mount bracket to screw down the top of the filter to the bottom
3.       A plate to cover the existing hole and cut a new one

Step 2:
Mock up everything.
Plate for hole:
1.       Put the part of the filter that has the hole on it on a piece of paper
2.       Trace the hole out on the paper
3.       Cut it out and draw the outline of it on the scrap metal.
4.       Using a grinder/metal sheers, cut out the design and make sure it fits as closely as possible to the shape of the hole

Bracket for top of filter:
1.       Measure the estimated distance from the top of the filter to the bottom (easiest way to do this is to measure the filter element)
2.       Its ok to measure 1 or 2mm shorter as it will be a tighter fit.
3.       Bend the metal strip accordingly to fit the height.
4.       Drill a hole that fits the screw and nut.
5.       Mark where to weld the base of the bracket.

Mounting points for the carb:
1.       The carb uses a “socket” type bell mouth where you need to connect the filter to and tighten down with a hose clip. This won’t work with the filter so we need to make tie downs.
2.       Make little L shapes out of the scrap metal strips you have.
3.       Mark where you want to weld the bolts
4.       Drill a hole on the L shapes and put the bolt through then tighten the nuts to hold the bolts down.

Step 3:
Weld everything
You weld everything all at once to reduce the cost (if you are not doing it yourself) of the welding and the trips to the shop you will be visiting.

1.       Weld the back of the bolt to the L bracket (DO NOT WELD THE NUTS)
2.       Weld the metal filler plate you made to the back of the filter
3.       Weld the nut to the top of the top mount.
4.       Weld the bracket for the top mount where you marked it.

Step 4:
New hole for the air filter
1.       Place the carb on the bike.
2.       Put the assembled air filter on the bike at the carb to see if it hits anything.
3.       Once you know it won’t hit, mark at least 4 points on the back of the filter with a marker pen of where the bell mouth will be.
4.       Take off the filter and the carb
5.       Put the carb on the back of the filter again and place draw a circle where you had marked earlier

Mounting point for the air filter
1.       Clamp down the L shapes with the hose clamp onto the bell mouth of the carb
2.       Put the carb to where you drew the hole.
3.       Mark the points where the bolts are touching the filter
Note: putting marks on the L shape and the carb is good so you can remember the position of the L shapes in case you need to remove the hose clamp for any reason.

Step  5.
Cut ‘er up!

Intake Hole
1.       Using a grinder with a small cutting disk, slowly cut the hole you had marked
2.       It doesn’t have to be perfect and it is preferable if the carb can actually fit in the hole (which it won’t but it’s good to have that size)
3.       Once the hole is cut, deburr it with a grinding disk to make sure you don’t cut yourself.
Note: this is easier achieved if you use a used cutting and grinding disk (because it is smaller so easier to cut). If you don’t have them, to go a garage or metal shop and just ask for them. They will give it to you for free.

Air Filter Mount
1.       Measure the diameter of the bolt
2.       Use a drill bit that is 1mm larger than the bolt.
3.       Drill out the hole and clean it.

Step 6:
Paint the back
1.       Paint the back (inside and out) with some paint
2.       This needs to be done because after welding, the metal rusts easily. This will stop it.

Step 7:
Mount it all up and have a look.

Completed Air Filter Side

Completed Air Filter Front

Completed Air Filter Side

Went old school to make the patch as it was late at night. Didn't wanna wake the neighbors 

Almost Perfect Fit

Mocking Up

Test Fit

Welded Nut To The Mount

Another Test Fit

Welded Up The Patch And Cut The Hole

Mockup Of The Mount Points

Prepping For Weld

Second Mockup

All Welded Up And Connected To Carb

Side View

Yes I did announce that I won’t be posting guides for a while because my bike was in the shop. But I thought this would be useful for those who might have the same issues I have as I am encountering this while they are doing up my bike.

By Vy


  1. This comment has been removed by the author.

  2. Wow, that’s one wicked DIY. It’s amazing how those scrap metals can be used for projects such as these. Thanks for sharing this, it’s a good point of reference. Anyway, how’s your bike? Is the air filter performing well?

    Rosemary Bailey @ WabiCorp

    1. Thank you for the compliment, yes the bike is working great now.. Had to replace the carb with a tried and true Harley carb tho

  3. You did an awesome job there. And it seems quite easy, as long as you have the tools for it. Doing it themselves could save people a lot of money. It may not have the same quality as the branded ones, but still a good way to go. Anyway, thanks for sharing this post with us. Have a great day!

    Bernice Parsons @ Badger Anodising

    1. Hey there.. Thanks for that... I generally use of tools that one can buy from a hardware store.. Nothing special so others can try this out too... I agree.. May not be as great but it works well Haha..