Re: *Why* aftermarket air filters (UniPods) affect fuel mixtures in CV carbs.

[FJ1100mjk]

Love the exchanges on this recurring subject. Keep them flying.  

I run the OEM air boxes on my FJs and although they're pain, you learn to deal with them and create your own methodology of their removal and install.

I run the ethanol blends, and if your thoughtful of it's use in your bikes, you can run it without problems.

[JMR]

Modern airboxes are very good but they at least double the volume of the ancient FJ design and generally benefit from forced air at speed. Fit a Hayabusa airbox to an FJ.

[movenon]

Mine seems to run fine with the UniPods and set up as follows.  

1990 FJ 1200 stock engine with Cobra F1s
#155 Air Pilot Jet
#42.5 Fuel Pilot Jet
117.5 main Jets
Adjustable needle clip in the center position.
Fuel/Air screws out 2 3/4 turns
Home altitude 2605 feet.  Local rides up into the 8000 foot level.
George

[FJ_Hooligan]

"sport" air filters are less restrictive for air flow - well know fact.
That mean when engine sucks in air, it is easier to do that.

With OEM filter while air is sucked in to engine, MORE vacuum is created in air box.
More restrictive air filter (or dirty) mean more vacuum. So engine must use more energy to take in enough air in to cylinder and because air is "thin" cylinder will be not full in 100%.
And vacuum works in carburettors as well. More petrol will be suck out from jets due to difference in air pressure.
After installation "sport" air filter we have less vacuum in air box. Engine loose less energy, can take more air with every cycle, air velocity is reduced and that mean better cylinder filling.
Vacuum is the reason why we need adjust carburetors after fit new filter. No extra fuel will be sucked out from jets - we got leaner mixture.

Also that is the reason why many "normal" users describe engine work as ,,smooth" after filter replacement.
Quick change in throttle position don't create big difference in vacuum in air box. Those changes due easier airflow are smoother..

Absolutely NONE of this applies to a Constant Velocity carb.  The only vacuum that affects a CV carb is the vacuum created by the VELOCITY of the air flowing through the carb throat.  Put in a less restrictive filter and the velocity slows down.  At a slower velocity there is LESS vacuum in the carb which makes the slide move to a lower position to speed the air back up.  Now the needle is in a lower (leaner) position.  Engine vacuum stops at the throttle plate.

[Mark Olson]

Well geez guys , I bet you all could argue a ham sandwich . 

How bout this ..... If you wanna haul ass with the throttle pinned get a set of uni-pods and a jet kit .  K&N filters flow air too but don't filter as well.

                    .......If you stay below 6k rpm most of the time there is no benefit in power adding the aftermarket filters , only ease of filter cleaning.

Adding the free flow filters and jetting the carbs will increase max power just enough to make your clutch slip ..

[Country Joe]

Don't forget to run only motorcycle oil to make maximum power as well 

[FJ_Hooligan]

Well geez guys , I bet you all could argue a ham sandwich . 

Really?

Once again, you (not you Mark) can't put crap info out there and not expect to get called on it.

The freakin moon is made of cheese and if you use the front brake it will throw you over the handlebars.

[Mark Olson]

Well geez guys , I bet you all could argue a ham sandwich . 

Really?

Once again, you (not you Mark) can't put crap info out there and not expect to get called on it.

The freakin moon is made of cheese and if you use the front brake it will throw you over the handlebars.

Just having some fun with this topic ... velocity vs. volume and its effects on jetting .. 

Yes you are correct with your post about velocity  .. not the cheese though 

[FJ_Hooligan]

Does that mean you don't use the front brake?  :-)

[JPaganel]

Well geez guys , I bet you all could argue a ham sandwich . 

What kind of ham we talking about?

[Bones]

Baked with a marmalade coating on it..

[Mark Olson]

Does that mean you don't use the front brake?  :-)

Try not to , I don't wanna fly over handle bars..

[FJmonkey]

Baked with a marmalade coating on it..

What kind of marmalade?

[rlucas]

Baked with a marmalade coating on it..

What kind of marmalade?

Synthetic.

[FJmonkey]

Baked with a marmalade coating on it..

What kind of marmalade?

Synthetic.

Synthetic.