Why would you cover half the intake?

[Guest]

I'm going through an old GS850G and came across this; a plate riveted over the intake covering approximately half of it. I pulled it off, but cant figure out for the life of me why someone would do such a thing. Any ideas?

Do I need to get a new rubber intake snorkel? Or can I just run it through the hole on the back of the intake box?

PICS:

https://imgur.com/a/P2uRL6b

[Rob S.]

When I switched to pods from the stock air box on my Suzi, I had to cover about 90% of each pod with tape to get it to run well until I had it jetted.

[Redman]

Welcome to the GSR.

I cant explain it entirely, but have seen many comments here that the 850 in particular is sensitive to any changes in the in the air intake.
I suspect that plate was trying to restrict the airflow (to create the vacuum needed to operate the diaphragm on the CV carbs) about the same as the snorkel would.

[Steve]

There is no way to "create the vacuum needed to operate the diaphragm"* by obstructing the intake. Somebody has attempted a bodge to fix the problem of a missing snorkel. You would be MUCH better off with a snorkel. The problem is that they are hard to find by themselves, without another airbox.

*That vacuum is created by air rushing through the venturi. If you block off the intake (to "create vacuum"), there won't be any air to rush through the venturi.

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[stlstl]

You would be MUCH better off with a snorkel.

So I have to have that, eh? I'm finding a few on ebay, but they all look pretty ratted out.

[bwringer]

Yep, you gotta have the snorkel.

There's a strong chance (but I can't confirm... Steve may have some insight) that the shaftie snorkels are all the pretty much the same, so you may be able to scare up a ratty airbox with a snorkel from another GS shaftie and perform a transplant. Hard to say, since it's not listed as a separate part number.

In any case, if you could find a snorkel-adorned airbox from any other GS850 model, G or GL, any year, you should be able to transplant. If I faced this problem, I'd head downtown to ye olde motorbike boneyard and I bet I could scare up something pretty quick. You could also post in parts wanted; there are some folks parting out bikes. I don't know that a lot of shaftie airboxes get listed on fleaBay, but they are certainly available.

Back in the ignorant '80s, it was depressingly common for people to just remove airbox lids, snorkels, and such in search of increased airflow without bothering to do the requisite testing and rejetting. Or they'd interpret the resulting flat spots and leanness as increased performance somehow.

I guess it's not really an '80s problem; people still do similar dumb stuff with modern fuel-injected motorcycles, too. Over on the V-Strom forum, people commonly remove the secondary throttle plates and interpret the resulting increase in throttle jerkiness and abruptness as more power.

[Gorminrider]

I'm going through an old GS850G and came across this; a plate riveted over the intake covering approximately half of it. I pulled it off, but cant figure out for the life of me why someone would do such a thing. Any ideas?

I can't see that as having much effect except at highest rpm...it looks like an attempt to enrich the engine. ..Air is compressible(but air compression is "work") so the effect is not simple (the stock airbox is also somewhat "restricted" comparing the surface area of the intake to the possible demands of the engine seen as an airpump...) ...At low rpm (and less air demand from the engine) it'd likely have no effect...all in all a bit like a dirty airfilter?

[Steve]

Besides restricting the intake to a specific size, the snorkel also directs the air inside the airbox to minimize turbulence. Having a rectangular opening with sharp edges is a somewhat ideal formula for turbulence.

Brian, as much as I delve into trivial minutiae (that's directly from the Department of Redundancy Department ), I can not guarantee that all the snorkels are the same.

I do know that the 650s are out, your search will have to be restricted to 850, 1000 and 1100 shafties.

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[Danie.e]

Careful study of airflow and the phenomenon of pressure waves led to the design of the air boxes. It is possible to get more airflow per cycle than the actual capacity of the engine and I have seen figures like 110% in various articles.

It would seem that to remove the air box one actually reduces the output of the engine and mess with the smooth transition from idle to WOT. People tend to "falsely" believe that to remove the "restriction" of airflow ( the air box ) they actually increase performance whereas the air box actually acts as a stationery (Item without moving parts) super charger.

My exposure to small IC engines in the model aircraft industry led to a lot of experimentation with in and outlet systems to increase power. By just adding a venturi to the inlet of a 10cc nitro engine carb, one could for instance increase RPM with anything from 400 to 1600rpm depending of the diameter of the venturi opening. I found in numerous occasions a engine performing better inside a cowl of the model than when the cowl was removed. The harmonics in a tuned pipe on a two stroke maybe explains it best. Just as optimal wavelength in the exhaust increase power, so will optimal flow of air into the carb also increase engine power.

[Burque73]

In regards to turbulent air flow in the airbox, wouldn't a K&N filter create turbulence? A stock foam filter lets air come up from underneath while the plastic body of the K&N has a solid bottom.

Seems to me that would foul things up a bit if they're that temperamental.

[bwringer]

In regards to turbulent air flow in the airbox, wouldn't a K&N filter create turbulence? A stock foam filter lets air come up from underneath while the plastic body of the K&N has a solid bottom.

Seems to me that would foul things up a bit if they're that temperamental.

That does happen with K&N filters in some bikes (the KLR650's K&N, for example, is well-known to flow less than the stock foam because it has a solid "lid" and a large part of the surface area is blocked) but for whatever reasons, the K&N does seem to work fine in the GS shafties.

I'm not a K&N fan at all in any vehicle because I don't think they offer consistent filtration, and they don't seal well in many bikes. No one has really ever beaten a simple oiled foam filter element for high flow with excellent filtration. A stock foam element or a Uni element is best in a GS shaftie, and they last a long time.

That said, I've seen stock GS foam elements that have deteriorated over the years, so if yours isn't nice and springy any more, order up a new one. Foam crumbles aren't good for your engine.

[Burque73]

Good to know, Brian, thanks.

My foam filter is pretty new and I plan to keep using it. I have a k&n on the shelf that the P.O. used, but never really warmed up to the idea of using it myself.

[Steve]

If you look inside some (not all) pod-type filters, there is a bit of a radiused edge to help smooth the airflow a bit around the edge. Not quite as nicely as the stock intake boots or even velocity stacks, but it's enough to be effective.

Just for fun, next time you have the airbox off, start the bike, let it idle. It will idle all day long with no problems. Blip the throttle, you will wonder what happened. It acts like an accelerator pump has been disconnected. You will have a hard time getting the engine to respond to the throttle. Now, without changing anything else, take a shop rag, fold it in half, cover the inlets of the carbs. Waste a couple of zip-ties, hold the rag to the outer carbs with the zip-ties. Not only will the engine respond better, it's actually good enough to go for a test ride.

Regarding K&N filters: I have heard all the stories about lack of filtration. Especially those who say that the increased airflow is because there is less filtration. Regardless, all three of our bikes here have K&N inserts in the stock airbox with no problems noted. My son also has a K&N on his diesel dually truck. He hauls a heavy load, so there is a LOT of airflow involved. No problems there, either. One key is proper maintenance, which many either don't know how to do, or simply don't do.

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[stlstl]

Well fellas, this place saves another. This bike is a whole new machine, I cant believe it!

So I sealed the rivet holes and put on a snorkel and it made all the difference in the world, you all were right. Surging issues it had before are completely gone and it feels like it gained a bunch of power. Its so smooth now and pulls like a train. Fixing the intake on top of going through the valve shims (not a one would let me even fit a 0.04mm feeler gauge) and going through the carbs all using the BikeCliff guides have completely transformed this bike. Thanks again!!

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[Steve]

Thanks for the follow-up, it's nice to know that we still guess correctly, ... occasionally.

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