Airbox vs. no airbox

[fxnteeth]

What would be an average difference with airbox no lid vs. no airbox in main jet? 10, 20, 40. I know there are other factors but someone please give me a ball park. I am having hell with my 38mm airstriker going straight to a unifilter with outerwear. Sputters at top end no matter how I jet my 85 250R. A mechanic told me they run better with the box and no lid. I have an airbox coming, just wondering where I should start my main jet. I am at 170 now. Where should I start with the airbox installed.
thx
Jarrod

[Chazz of Blades]

Depending on riding conditions it's normally iffy running without a lid, or especially a box.

Unless you enjoy cleaning your carb after every ride, alot of trash can get in riding open.

[Xpress]

Do a plug chop to determine if you are running rich or lean, and then you can determine if you need to go up in your jetting, or down in it.

[RubberSalt]

It really depends on the air box setup.

On my YT175, it ran extremely rich(before tuning) with the air box. I stuck a clamp on filter and it ran somewhat lean.

The difference was about 80 on my main jet(28mm carb) and porting ect...

The filter was getting dirty extremely fast, so i added a pre filter. It didn't effect the jetting at all.

[pantera1975]

Could be a bad coil. Thats what I had happen

[Red Rider]

What would be an average difference with airbox no lid vs. no airbox in main jet? 10, 20, 40. I know there are other factors but someone please give me a ball park. I am having hell with my 38mm airstriker going straight to a unifilter with outerwear. Sputters at top end no matter how I jet my 85 250R. A mechanic told me they run better with the box and no lid. I have an airbox coming, just wondering where I should start my main jet. I am at 170 now. Where should I start with the airbox installed.
thx
JarrodJarrod, Ive been using a K&N airfilter for the majority of my 250R's life (24+ years), along with a heavily ventilated airbox lid. A few years back it was finally time for a new K&N airfilter, so I picked one up along with one of those outerwears, that I'd been hearing so many people talk about on the boards. So, I put on the new airfilter/outerwear combo, and damned if I couldn't get my bike to run cleanly. It ran fine before, but now it's sputtering on top-end no matter what I do with the carburetor jetting, and the only thing that changed was the airfilter/outerwear combo. I finally removed the outerwear, and that solved my sputtering problem.

My brother was having a similar top-end sputtering issue with his 250R, and he has cut away so much of his airbox, that it is basically an open airfilter now. Because his airfilter was so exposed, he thought he'd use an outerwear on it. Result: Top-end sputtering that jetting wouldn't cure. After I got mine running cleanly again, I suggested he remove his outerwear also, just to see if it would help. So, he removes it, and problem solved. I think these outerwears are a little more restrictive than everyone thinks they are.

Also, if your bike was jetted properly before with the Keihin Airstryker, removing the lid should only require an increase in main jet size of 10 at the most. More than likely, you'll find you needed to increase it around 5-7. Sorry, but I have no guestimate for a no airbox setup.

[fxnteeth]

Thank you very much for that info and time it took to write it. That makes me feel much better. I just ordered an airbox off ebay. I will ditch the outerwear

[Bretmd94]

Thank you very much for that info and time it took to write it. That makes me feel much better. I just ordered an airbox off ebay. I will ditch the outerwear

I can't help but notice that your in Louisiana, where are you going to be riding? I wont run a K&N in the dust. K&N has bigger holes for air and hp, but you also get dust though. If you need proof just test it out and look inside the carb after.

I do run K&N's in the sand though. I run outerwears as well to keep from clogging the filter with sand. My bike runs great. The outerwear will restrict flow and make a bike that ran well with out it run crappy. Just needs to be re-jetted.

I really feel its just something that you need to learn for your own riding situations.

In heavy dust, I suggest a foam filter that is well oiled and cleaned EVERY ride.

Sand, K&N with an outerwear for okay protection with out box lid off.

If you run no airbox.... well... I would avoid any water... Too much water in the oregon dunes for me to pull off the no airbox, I like to go fast over water.

[fxnteeth]

My plug chop is perfect at 170 main. Me and a honda mechanic have run the gambit on jetting this damn thing. It never seems to run very different after the jetting. I tested the resistance of the entire electrical system. coil, plug, stator. It all tested great as far as I could. I dont know if there are issues under load. It pulls like a champ until 3quarter throttle. It idles great. Starts on first kick (if it doesnt kick back and break my foot). I am going to try the air box when it comes in.
thanks