Pod Filter VS Airbox

[trbig]

I've been running pod filters on my XJ for years and love them. The ease of removal/installation of the carbs is a dream come true and I LOVE the growl I get from them.. BUT... I remember T.C. making a movie like this once, but I don't remember him getting on it like this.

I've had a stumble between 2-3k rpm that I can't seem to track down. I mounted my GoPro camara to the battery to watch my carb slides to see if I could see one dropping or something. I got out to the highway and shifted into 4th at @ 15mph, then slowly eased into the throttle until WOT and held it to redline. If you set the video setting on this to 480, or even 720, then you'll see what I am getting at.




http://youtu.be/MLRejaVHc3M



After riding the XJ, I could always smell fuel on me and wondered how. I figured it was just blowing back on me from the exhaust somehow. You can see that at higher speeds, the wind is sucking out more fuel than the engine seems to be. With as much as is spewing out, it makes me wonder how it runs so well at upper rpm? It doesn't look like any is even going into the carb?? You can see it get all over the camara, and really see it towards the end spewing from #3 and #4.. probably just because of better lighting on that side.

So, even though I still love the pod filters, there is definately something to be said about velocity stacks or the stock air breather for these bikes. With just pods, there has got to be wind sucking the fuel out still, and I'm sure a person could get better fuel mileage with one of the other setups. I may have to try this again with the pod filters on and see if I can still see fuel escaping.

Just thought this was intersting and worth posting about.

[motoman]

Interesting.........to bad the XJ had to be a bit of a PITA to deal with the removal of the stock intake.

[crazy steve]

Entirely typical for a individual and/or short runner intake....

The problem isn't the wind sucking it out, it's the column of moving mixture rebounding off the closed intake valve. If you strapped the bike to a dyno, you'd see the same thing. Velocity stacks help with this, the longer the better generally. A common-plenum airbox would help some, even two 'paired' filters although effectiveness would be quite a bit less.

Harley's do this too; the short intake runner has enough reversion that I never need to oil my K&N filter as it's always a bit 'wet'...

[WMarshy]

I recently read some of Dan Hodges posts about his dyno results and he said his bike made more power with less restriction on the intake. Even short velocity stacks had a negative impack on power output... That being said, I dont think it's practical to run no stacks or filters and if/when I ever use pod filters I'm going to cut the face (facing the engine) out of the air box so the pods are recessed in the box and shielded from the cross wind. I cant remember what member did this first...

[jwhughes3]

K&n

Isnt it just easier to KEEP the stock airbox, drill it for extra airflow and drop a K&N filter inside?

I run a K&N on Great Ranger and it runs fine.

John

[GARTHXS]

Holy crap that is a lot of gas

[skids]

After riding the XJ, I could always smell fuel on me and wondered how. (Snip)

I have heard that some members used pods within the protection od the airbox upper. They reported improvements. (for example Lanny Marsh?)

[trbig]

Isnt it just easier to KEEP the stock airbox, drill it for extra airflow and drop a K&N filter inside?

I run a K&N on Great Ranger and it runs fine.

John

No K&N for the XJ without modifying one and making one. The stock airbox on the XJ makes putting the carbs back in a major PITA, so many go to pods.

[jetmechmarty]

I don't think you're looking at fuel. The air moving into a jet engine sometimes looks similar. I think you're seeing condensation from the air moving rapidly into the carburetors.

[trbig]

Well, I was sure looking at a lot of fuel all over my camara afterwards. lol.

[ddragon63]

why do you wanna take your carbs off alot? Once they are tuned and set you should just leave them on and ride the thing... Just saying

[CaptonZap]

I don't think you're looking at fuel. The air moving into a jet engine sometimes looks similar. I think you're seeing condensation from the air moving rapidly into the carburetors.

I think what they saw was fuel droplets, and what the racers call standoff. It is caused by the reversion of air when the intake valves are open and the piston is starting up. It seems to be a function of cam timing verses RPM.
On downdraft carbs, it isn't a problem, since it will fall, or get sucked, back into the carb mouth. Side draft, it's a different story. Some of the heavier droplets will fall out of the intake airstream.
As has been mentioned, velocity stacks long enough to contain it are the best answer. CZ

[T99Ford]

No, fuel injection with a tuned airbox is the best answer, ha ha! Tod, are you running a 4-1 pipe?

[TopCatGr58]

Hey Tod,

Wow, nice panoramic view of all 4 carbs! In my video I did get on it several times taking it up to Redline and such, but just short bursts. But during those bursts, I can see small spritzs of fuel around the inlet bell ports as well. Mine had a stuck/broken float post and so my #2 carb was flooding at times, and in my video you can see me fiddling with the fuel hose trying to see if I can tell where the fuel is coming from....but I thought it was mostly due to the stuck float/flooding #2 carb as to why I was getting fuel spraying around while the filters were off! I'm pretty sure I was already running the richer 117.5 mains because I didn't film this until after I rebuilt my topend, and when I went to pods, I put the larger jets in to prevent burning holes in my new Wiseco pistons! On my after breakin dyno run, the readout showed that I could have possibly gone up 1 more jet size to 120. My plugs have a decent light tan color, so I'm not running too lean, but I'm not rich either.

Perhaps yours is jetted a little too rich? Or your floats a little too high/rich?
Are those XJ carbs, I can see the 4 inlet ports, but can't see the enrichener. Mine are also the later carbs, 81Sh, so they shouldn't be that different....still don't think they should be spewing that much fuel?

T.C.

[trbig]

We finally got my carbs figured out. (Yes, they are XJ carbs, and as I said, have the Dynojet kit.) As you assemble the carb slide, you drop the needle down and get that tab into it's hole, then on top goes a small washer, then the spring, then the metal cap and two screws to hold down on the spring. In my case, the small washer that goes on top of the circlip sitting in the groove was so small that it fit up inside the center of the spring. So, the spring was actually pushing down on the plastic donut thing with the tab that goes underneath the circlip. Over time, this was pushing that donut down the needle, thereby raising the needle and giving me a rediculously rich mix. It would idle OK and run WOT OK, but anything in between, it sputtered and popped. BAD.

So, the reason so much fuel was spewing out is because the needles were getting raised up so high. When I would take the top of the carbs off, the diaphrams would be SOAKED with fuel.

Thanks for the input, guys.