Stock airbox vs cone filter

[zummerp]

I’ve seen some passionate opinions on using the stock airbox, removing restrictions, or using a pod filter. I’m installing a 20mm carb with bigger jets on my ATM50-A1 w/ BBK tomorrow and was wondering pros vs cons of swapping the air filter. My biggest problem with the stock airbox is that the carb is harder to remove and reinstall with something on each side

[jeff84]

most of the time easy access to the carb is the biggest pro of a cone filter. they do flow better, but most stock air boxes can be easily modified to allow more flow. plus the stock box will add much more protection in wet conditions

[GrumpyUnk]

One additional feature in favor of the stock airbox is that if the float valve sticks, you won't have fuel flowing directly onto the top of the engine(crankcase). It will flow through the tube, and wander its way through the filter box and fall out at the back. If you were to have a backfire or spark, at least it would be a bit further away.
Once you get things tuned in, you won't generally be having to remove/install the carburetor with any frequency.

If you check the videos 90GTvert has done, removing restrictions don't seem to add performance, and in some cases, reduces it. He even reported less fuel economy with restrictions removed. YMMV surely applies...
In most cases, the difference in performance is very minimal once severe restrictions are lessened. Remember, the air all has to fit through a hole(venturi) that is smaller than a quarter, and closer in diameter to a 5 cent piece. The airbox doesn't do much restricting compared to that.
tom

[artman4life]

i personally like the cone filter just for the more clean look. i also removed the emissions junk too. for me it just makes everything more simple and basic to work on without the clutter. that being said you have to also be willing to tinker and tune to get your setup dialed in. in the end i thinks its more of how much you like to "play" with your tune vs just turning the key and ride.

[zummerp]

Is it worth trying to upjet and get a little more top end without modifying the stock airbox or will I just end up way too rich?

[greginisn]

I'm a fan of a quieter scooter altho some people are of the opinion that louder is safer, and would opt to keep the stock air box. If you can put a light smear of a DC silicon grease on the inside of the manifold and the inside of the air box hose you will find the carb slips out of and back into position very easily. It's not like you will have to be digging into the carb every week anyway. I hope.


Greg

[GrumpyUnk]

If you think the stock box is hard to remove and install, wait until it gets some time in use, heated. They become very inflexible, and difficult to do much of anything with. One was distorted and didn't fit over the carb inlet. I used a heat gun to make it flexible again, and was able to straighten it out enough to fit it over the inlet. It retained the correct shape, but is still very stiff and not the easiest thing to work with. Using some lube on the inner diameter of both rubber fittings makes removal and installation a lot easier.
tom

[zhono]

I just bought a cheap VIP Future Champion(cy50a) that was pretty beat up. Gas was ouring from the carb, and the air box could no longer attach to the carb. Bought a replacement carb and a cone filter on Amazon, popped those in(and new plug & oil) and now it starts right up and runs okay, though it does chug gas big time according to my gas gauge. Anyway, on the air box there were 2 hoses, which are now not attached to anything, and I capped them off. What are those 2 hoses,and what should I actually do with them? Also, is there anything I should be doing/changing now that I removed the air box and installed the cone filter?

[GrumpyUnk]

Yow!@! Don't cap those hoses.

If you had fuel running out the airbox, you very likely have a sticky float valve. You can remove the carburetor, flip it over, and remove the three screws holding the float bowl. If yours is 'tamperproof', then you will have to drill the fasteners and remove using an 'easy out', or left hand drive drill, and replace with normal screws, OR replace your carburetor. You could also have a punctured diaphragm on the vacuum operated fuel petcock. If punctured, the fuel can get pulled into the intake via the tube connecting the petcock to the intake elbow. It may just pull a little, but will make the fuel:air mix over rich.
One hose is to provide ventilation to the crankcase. When the piston goes up on compression or exhaust, there is a slight vacuum formed in the crankcase. When the piston comes back down, a slight pressure is formed. Witout ventilation, you'll likely cause problems with the seals(leak oil) or with condensation forming that mixes with the oil, and forms a slight acid. Not good. It can also form 'pudding', a creamy mixture of water and oil vapors. It eventually will clog things up. Better to not have it form...
The second hose will have to be identified better. It could be the vent to the CVT case, or to one of the emission control items used, or the vent of the fuel tank. Follow it and report.
tom

 ADDED:  When you install a cone filter, you likely reduce some of the airflow limits built into the system, and should monitor your engine for running lean.  (Once you fix your fuel oversupply problem, you may notice it is running lean, hot or even pinging)

[eclark5483]

I advocate airbox, especially if it's a 2 stroke. The reason being, most engines on bikes are tuned to the amount of flow coming in through the venturi. This is what the airbox is helping to regulate. To explain this better, 2 things to cover.. 1, is when you pull back the throttle on the carb, you are not letting in more fuel, you are in fact, letting in more air. And 2, you can think of the air coming in the same way the vacuum cleaner works with a corner attachment. The tighter/smaller the hole, the tighter the suction of gas being sucked down into the piston, then, when you remove the corner attachment and put on the regular one, you still have that suction, but it is not as strong. When you put a cone/pod filter on over an airbox, you are NOT letting more air in, you are changing the atmospheric pressure and suctioning power, reducing the amount of fuel that can get pulled through the venturi. This is why when you change to one you almost always need to upjet to compensate. That's not to say a little bit more air over stock isn't helpful when you do a BBK. With the larger displacement, some usually like to just take off the snorkle. This is what I did on my TaoTao's. I do have pod filters, but for a more precise tune on the dyno, testing showed the airbox was a better choice. With a cone filter, you usually end up having to duct/electrical tape it a bit to get just the right amount of suction. This will affect acceleration as well as top speed.

[zhono]

One of the hoses, now that I think of it, was not attached to the air box and was capped off by the previous owner, though I couldn't tell you at this point which was which. I can tell you, one of the hoses comes off of the intake manifold(between the carb and engine) and the other is a few inches away, coming off of the front of the engine. Pic, they are the top two: ibb.co/bzJpVS

Engine is a 4-stroke, by the way. I'd use the original air box, but as I said the part to connect to the carb is warped(and shrunk?) and I don't have money for a new one. Had to spend everything I had getting the scooter and the parts I got, plus registering the thing. Maybe I can heat up the plastic and for it back on to the carb.

Edit: Okay, so I just used one of those butane torch lighters to heat up the rubber and fit it onto the old carb, then lightened up the clamp. Going to let it sit overnight, and reinstall the air box tomorrow when it's not raining. So now I just need to confirm which hose goes where on the air box. I'm guessing the hose coming from the intake manifold connect up to the tube that runs right back into the carb, and the other hose goes to the little round bit where the air first enters the air box? Also, thanks for the help/advice. This is the first scooter related forum I've found that seems to actually have active users. Hopefully I can get the air box sorted, so I can move on to my lighting/signal mods.

Edit2: Hose on the intake manifold; vaccum line, as I'm sure you guys already know, but I did not. I do now. Neither the old carb or the new one actually have the nipple on the carb to connect up to the vacuum line, so I guess that's why the line was capped ff to start with. So I suppose I should keep that one capped off. Going to reinstall the air box now, but man it's cold out at the moment.

[GrumpyUnk]

The two lines in your picture that branch from the intake elbow(manifold if it were more complex) are used fore 1)emissions control vacuum operated valve and 2)vacuum operated petcock valve.
The left hand wire goes to either a fuel tank vent valve or to an emissions 'canister' valve that stores fuel tank vapors or crankcase vent vapors. At least the ones I have seen have a canister with MULTIPLE connections, and what appears to be a vacuum operated valve at one end.
If you convert to manual petcock, you can plug the vacuum control line, put a cap on it, fold it over and clamp, or leave it connected to the remains of the petcock. If there are no fuel lines connected, the petcock will do nothing harmful.
The emissions vacuum line is subject to more inspection, depending on what it controls. If it involves crankcase ventilation vapors, you will need to make sure the vapors are routed to the intake hose(after the air cleaner) or to atmosphere, protected from blowing vapor all over the rest of the engine/CVT assembly. A 'catch can' is not a bad idea, though a length of tubing clipped to the frame, and routed up will allow vapor flow, and make it hard for any liquid to leak(liquid would slowly drip/drain back down the walls of the tube.)
tom

[zhono]

The tube on the right(the gray one) isn't actually the issue. It was the black one on the left, and the one further up, not connected to the intake at all. I do now know what each of them is/does, at least. I actually just got done situating them. The vacuum line is now capped off, since the carb doesn't use it, and the other line I added a spare/new fuel filter and then secured it up high, in the general area of the gas line. The actual spot on the air box where there's supposed to be a hose, I capped off. Also, during this process, I managed to snap off(what I now know is called) the snorkel. I've seen people discussing removing it anyway, and it seems to not have effected anything, so I guess it's fine. At some point maybe ordering a whole new air box on Amazon Prime for $12 is a good idea. But for now it seems good. Also, my gas gauge seems to be the cause of my gas-guzzling issue(i.e. there was no issue), as actually looking in the tank reveals it's like 3/4 full, while the gauge is between empty and 1/4. Still a pain putting gas in at the pump, with that metal bar blocking me from actually inserting the nozzle.