Low profile air filter

[weefek]

Welcome back to myself after a long and uneventful winter. The weather has finally changed around here so I pulled the bike out last week.

I've been browsing the forum on and off all winter but haven't posted at all.

Surprisingly, the bike fired up immediately and runs exactly like it did when i put it away in November. Zero issues...

Now I'm returning to something I tried to do last summer but didn't have time to mess around with it.

I bought a low profile air filter (I forget where from, might have been Sick before they closed). See the picture (not exact one but similar).

Anyways the issue is this: When running said low profile filter, the engine doesn't like it. Less power, Less torque, More 4 stroking, and it won't top out at nearly the same speed as when I run the stock filter (Bofeng carb). To me (a 2-stroke layman) less restriction would mean more air and leaner burn = more power. But what do I know?

The engine doesn't get any warmer than normal and the spark plug gives me no information (this from last year, I don't have any spare plugs at the moment to run a new plug to get with).

Anyone know what's going on?

Thanks guys.

 

[Whitewill1412]

I would think you need to go richer on the needle to accommodate the added air flow

 

[weefek]

I would think you need to go richer on the needle to accommodate the added air flow

I don't think it's that simple. @DAMIEN1307 @ImpulseRocket please help me out here guys. Damien I know you're not a genius 2 stroke tuner or anything but you've been in this game for awhile and I think you use one of these

 

[Nickt919]

Hey bud...I've been wondering where you've been. Glad to see you back.
It does not take much of a change to throw a tune out of whack. This is the exact reason the veterans here tell people to try one change at a time when tuning so you know how it affects the tune. Sometimes one small change make big a difference in how it will run.

I would try no filter to compare to the stock filter performance. Then the low profile filter with adding some choke after its warm to see how it affects the tune. These different things can help you try to determine if you're new filter is actually letting in more air or more restrictive than the stock filter.
Something else to consider...the stock filter cover will have a much different affect on how the air enters the carb venturi than the low profile. This is separate from the volume of air.

I know this is not what you're looking to hear...but...., If it was mine...depending on how well it runs with the stock filter...like if it ran perfect....I'd leave the stock filter on instead of spending time chasing a tune.

 

[ImpulseRocket]

Welcome back to myself after a long and uneventful winter. The weather has finally changed around here so I pulled the bike out last week.

I've been browsing the forum on and off all winter but haven't posted at all.

Surprisingly, the bike fired up immediately and runs exactly like it did when i put it away in November. Zero issues...

Now I'm returning to something I tried to do last summer but didn't have time to mess around with it.

I bought a low profile air filter (I forget where from, might have been Sick before they closed). See the picture (not exact one but similar).

Anyways the issue is this: When running said low profile filter, the engine doesn't like it. Less power, Less torque, More 4 stroking, and it won't top out at nearly the same speed as when I run the stock filter (Bofeng carb). To me (a 2-stroke layman) less restriction would mean more air and leaner burn = more power. But what do I know?

The engine doesn't get any warmer than normal and the spark plug gives me no information (this from last year, I don't have any spare plugs at the moment to run a new plug to get with).

Anyone know what's going on?

Thanks guys.

For starters, the trick to getting a spark plug to tell you exactly what is going on during a run issue is to cut the ignition during that run issue. That is the entire idea behind a "plug chop" in order to read the plug for specific circumstances. As the conditions change while the engine runs, the plug self cleans and can change visual condition once you enter a different throttle position.

The Layman's explanation for carb tuning is, more air = leaner = more fuel. The dynamics between airflow volume, manifold vacuum, intake velocity, and the level of turbulence in the intake path will all determine the jetting needed. Adding that filter vs. the stock style may have balanced out some of those factors in opposition to others.

The suggestion to adjust the needle is a good one. The tune could just be slighly out of wack and just needs a small change. It's also the easiest thing to try and see if you observe a change.

 

[GW's Motorized]

I had to adjust the needle height when I added a sbp air filter to my bike. It's not the lo pro, but it still changed the tune due to the higher air flow.

 

[LewieBike]

You ever looked at the small 50 to 80 cc motorbikes from Japan back in the 1960's? They, as a rule had an ample sized either pleated paper element or a foam in a metal cover with a rubber snorkel to the carb. Some these bikes has rather elaborate shapes like the step-through Hondas and rotary valve 2 cycles. The airfilter you're showing is what is frequently called in the motorcycle modding world as a "pod filter" And they're kinda crappy to use with bikes whose carbs were tuned to run with either an airbox or remote filter/airtube. Carb intake tuning is a science that the motorcycle industry spends a lot of time, money and design on.

Now frankly our little, primitive 14mm carbed bikes don't have much in the way of velocity throught their engines or carbs, but if you look at similar power level engines on 50cc mopeds and small Nopeds and little kid's 50cc bikes, the manufacturers do spend a bit of design effort on their airfilters. The Yamaha PeeWee 50 for instance; look up the replacement airbox of that bike. I would think trying to fit somethng like the PW50 airbox to our engines would be problematic because of the seat-tube..

 

[GW's Motorized]

You ever looked at the small 50 to 80 cc motorbikes from Japan back in the 1960's? They, as a rule had an ample sized either pleated paper element or a foam in a metal cover with a rubber snorkel to the carb. Some these bikes has rather elaborate shapes like the step-through Hondas and rotary valve 2 cycles. The airfilter you're showing is what is frequently called in the motorcycle modding world as a "pod filter" And they're kinda crappy to use with bikes whose carbs were tuned to run with either an airbox or remote filter/airtube. Carb intake tuning is a science that the motorcycle industry spends a lot of time, money and design on.

Now frankly our little, primitive 14mm carbed bikes don't have much in the way of velocity throught their engines or carbs, but if you look at similar power level engines on 50cc mopeds and small Nopeds and little kid's 50cc bikes, the manufacturers do spend a bit of design effort on their airfilters. The Yamaha PeeWee 50 for instance; look up the replacement airbox of that bike. I would think trying to fit somethng like the PW50 airbox to our engines would be problematic because of the seat-tube..

By 50 to 80cc Japanese bikes do you mean the trail line up (trail 90,trail 70, z50)?

 

[ImpulseRocket]

You ever looked at the small 50 to 80 cc motorbikes from Japan back in the 1960's? They, as a rule had an ample sized either pleated paper element or a foam in a metal cover with a rubber snorkel to the carb. Some these bikes has rather elaborate shapes like the step-through Hondas and rotary valve 2 cycles. The airfilter you're showing is what is frequently called in the motorcycle modding world as a "pod filter" And they're kinda crappy to use with bikes whose carbs were tuned to run with either an airbox or remote filter/airtube. Carb intake tuning is a science that the motorcycle industry spends a lot of time, money and design on.

Now frankly our little, primitive 14mm carbed bikes don't have much in the way of velocity throught their engines or carbs, but if you look at similar power level engines on 50cc mopeds and small Nopeds and little kid's 50cc bikes, the manufacturers do spend a bit of design effort on their airfilters. The Yamaha PeeWee 50 for instance; look up the replacement airbox of that bike. I would think trying to fit somethng like the PW50 airbox to our engines would be problematic because of the seat-tube..

I am aware of the filter he is running because I run the same one on my Phantom 85's Bofeng carburetor. It's better than the stock open cell foam block for filtering, and in terms of useable area, it has more than the stock filter too. The element is a washable and reusable cotton element that can also be oiled if desired. That engine has zero issues with kissing 9000rpm and doing 50mph through a skinny little 14mm carburetor and OZ Reed block that came with the engine.

They flow more than enough air, and the performance of the bike changed not at all. Well, other than not ingesting sand and grit through a bit of sponge with holes you can see through.

 

[LewieBike]

By 50 to 80cc Japanese bikes do you mean the trail line up (trail 90,trail 70, z50)?

I've owned a lot of small Japanese trail bikes, many Trail 50's and Trail 90's, even one '71 Trail 90 that had a Powroll 125cc stroker kit, that one was scary and had to be run on 110 octane aviation fuel. Edited: The Honda 50's I'm talking about are the early 'adult size' step throughs like the C-100 and C-105 Trail 55.

Also a few Yamaha 50's, 80's and 100's, their step-throughs and Trailmasters, a couple TS90 Suzukis and a Hodaka RoadToad. Every one of these bikes ran better with the stock intake and exhaust systems, and it's not like I didn't try. Having the air from the filter enter the carb as undisturbed state as possible, ( no turbulence..) helps. I believe the pod filters create too much turbulence.

If you have seen an older pushrod OHV Honda 50 they have this slightly "S" shaped rubber tube intake from the filter's airbox to the carb, if you take that off and put a pod filter on, you will lose the ability to rev the engine fast enough to break 25 mph. Those early Hondas made 4.4 HP at 8500 rpm and could return nearly 140 mpg if you didn't pin the throttle 90% of the time. More HP per cc than most HD's and British twins.

And they were all cast iron cylinder and heads with pushrods, not overhead cams, and their intakes and exhausts were best left alone.