99cc Predator air filter mod

I recently picked up a 99cc Predator engine from Harbor Freight in anticipation of an upgrade to my 1950 Schwinn Panther, which currently is running a 50cc Hua Sheng mated to a Qmatic transmission. The anemic HS is a nice engine, starts well, runs smoothly and is simply not enough Hsp to suit my needs. I'm 200 pounds, have hills to climb and a dog in tow. And I don't want to pedal which is why I have a motor bike in the first place.

So, I'm preparing the engine now and will purchase pulley and belt next month as money permits. Always on a budget, I'm now making up a do it yourself throttle control and some changes to the stock air box. The air box is the subject of this thread.

A couple of years ago I did a similar modification to a 79cc Greyhound engine which has pretty much the same footprint as the 99 Predator. The air box is also by all appearances the same. I don't like plastic and it is really the only thing I don't like about the appearance of the engine. A big plastic box. Gotta go.

I've seen others here use some cool looking round air filters, one of them from a Whizzer. I made my own for that Greyhound out of a double size tuna fish can and loved how it looked. I felt so clever.

Until I rode the bike. These engines are wide, so anything sticking out more than the original air box is an issue, in my opinion, based on my own experience with my build. A different bike might not be a problem, but for mine it was. My leg kept running into the air cleaner I had made.

So I went back to the stock plastic box, still not liking it, but at least my leg wasn't running into it. Then I modified the cover with one I made from tin, which was the prototype for the one I made today for the Predator which is the subject of these photos. Form follows function... I wanted it to tuck in close to the engine and get a good gulp of air while protecting the engine... and it does.

If you look at the stock plastic cover you can see there is a lot of wasted space, it being larger than it needs to be. While it is big, there isn't all that much air intake as you will see in the photos. My modification uses the original air box and doesn't need to be removed from the engine while doing so.

There are two tabs, one above and one below which received bolts holding the plastic cover in place. I cut these off with a cutoff wheel on a Dremel type rotary tool. This cuts down the size of the needed cover quite a bit, as you can see.
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SB

Now for the tin cover. Using tin snips I cut out a piece of tin with an extra 1/2" at each edge to give me something to fold over. But before folding the edges I marked out a grid to locate breather holes, first punching each one with an awl and small hammer. Then I drilled each pilot hole out to size with a 1/4" bit. I saw that I had room for more holes, so added a center hole to each "square". I cut the corners so that the edges could be bent in.

There are any number of ways to do the bend as this is not thick metal, pretty much the gauge of a tin can. I used a couple pieces of steel clamped together for the first two bends and did them by hand. I used to small wooden blocks for the other two bends. Whatever you have. After the edges were folded I soldered each corner so there wouldn't be any sharp edges.
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SB

I use the plastic piece inside the cover which is there to keep the foam filter from pressing up against the carburetor intake. So that spacer is left in place. I did some experimenting with filter materials with the Greyhound a couple of years ago and found that the stock foam filter is pretty restrictive. I tried using a cut down 3M scotch pad (I think that's what it's called) and it works great with an immediate improvement in power.

So that's what this Predator air box is getting. You can see in the second photo the stock foam filter, and the green colored 3M pad. Then the tin cover goes on and is held securely with two sheet metal screws above and two below.

I don't know that it looks as cool as the round air cleaners, but this tucks in even closer to the engine than the stock one did and I think it looks pretty good. It also helps to disguise what this engine is, along with the 49cc decal (thank you Cannonball2). I will probably paint the tin cover black to protect it from rusting and to make it blend into the engine more. And that's it.
SB

Bill and Andrew,
Glad you found the thread of interest.
I'm sure looking forward to fitting that engine into the Panther frame... going to be a tight squeeze. I think the power is going to be just right.
SB

Bill and Andrew,
Glad you found the thread of interest.
I'm sure looking forward to fitting that engine into the Panther frame... going to be a tight squeeze. I think the power is going to be just right.
SB