Suppose I have a GS425 and would like to add...

[MidWestCoast442]

...PODS. Yeah. I said it.

More specifically: the K&N single filter. Can it be installed inside the stock airbox? What are my options? What if I just removed or opened-up the lid to the airbox?

The bike uses Mikuni BS34SS carbs, but Dynojet doesn't make a kit for my bike. Is it possible to piece-together a set of jets & needles that will make things work well? Sounds like the trick is to use an appropriate needle.

Not saying that I AM going to do this. I just want to know if it's even possible to make it work right. Seems amazing/ridiculous that so many people have so many issues with these things. I'm probably going to need to do a carb rebuild soon. So if this is going to happen, then why not when the carbs are already off of the bike. Right?

[posplayr]

Just a data point for reference. I had an 1981 gs750ex (16v calif. Smog so already lean) and I replaced the stock filter in stock air box with a k&n filter element. It was a little lean but I never changed it.

[Steve]

OK, which are you going to do? Pods or an insert?

An insert in the stock airbox probably won't need any jetting changes. Maybe up one size on the mains, if anything.

Pods, on the other hand, will open up a can of worms. Not impossible, just not "plug and play".

.

[MidWestCoast442]

So it seems like there are 3 options, K&N insert filter with stock box. K&N insert filter with box that has been "opened-up". And K&N filter pods (I think they make one big pod filter that connects to both carb boots...no?) with no box.

Which one am I going to do? I would like to do whichever option will realize the most performance gains...preferrably with minimal headaches.

I like the the idea of leaving the box in-place and opening it up for better air flow. Seems like it would be the equivalent of pods with a stock look. Right?

[Steve]

I would like to do whichever option will realize the most performance gains...preferrably with minimal headaches.

Well, none of those options is going to transform your bike into a beast that pulls your arms out of their sockets. Even the best of mods might allow the stock 40hp to increase to 42 or 43, but I would not expect even that much without adding a header. Changing cams (if any are available) might get you over 45hp, but that is a lot of effort and expense for minimal gain on a small bike.

I would go with the "minimal headache" route and do the K&N insert in the closed airbox.

.

[MidWestCoast442]

Yeah. I'm aware that it isn't going to gain 10+ HP. Or even 5hp.

Duly noted. I'll get the insert and rebuild the carbs with stock jets...or go up 1-2 sizes on the mains for 2-1 exhaust.

Recommendations for 2-1 exhaust??

[Steve]

Recommendations for 2-1 exhaust??

Someone who knows more about the twins will have to answer that one.

.

[MidWestCoast442]

Okay. Thank you

I actually started a separate thread regarding that issue. No responses yet.

[huntb]

2-1 exhaust and drop in I would up the mains by about three sizes and call it good. You might want to shim the needles a bit too

[MidWestCoast442]

Thanks. What about the pilot?

And how does one go about shimming the needle?

[Steve]

Thanks. What about the pilot?

And how does one go about shimming the needle?

The only reason to change jetting is because you have reduced the restriction imposed by a stock airbox.

At idle (and low-throttle openings), it is the throttle butterflies that cause the restriction, so there is no real change in airflow, therefore no need to change the jetting.

To shim the needles, you need to replace the thicker nylon spacer that is above the clip with a stack of washers that is thinner than the spacer. There is a spring that pushes the needle UP to its seated position. Reducing the thickness of the spacer above the clip allows it to be pushed a bit higher, which richens the mid-range.

.

[MidWestCoast442]

No need to change the jetting at all? Or no need to change the pilot?

[Big Rich]

Steve means the pilot. The stock air filter isn't very restrictive when the bike is just at idle (and using the pilot circuit), so an aftermarket filter provides just as much air flow at idle.

While this is true of older bikes (before EPA requirements) later models can benefit from a larger pilot jet.

[MidWestCoast442]

Thanks, Rich