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
Note:
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