What is this hole in the intake box for? and a carb question

[marshall]

I've got a 1980 (maybe '81, I always forget) XS1100 midnight special, and there's this funny hole on the bottom of my intake box. I can't figure out whether I ought to plug it up or not. I've had other bikes with what I always believed to be a water condensation drain here, which would make sense, but this hole just seems so large that it would suck up a lot of dust (and be a source of significant vacuum leakage). It's downstream of the filter. The microfiche describes it as a "seal" and "cap" (see #s 50 and 51 below), but my "cap" has a 1/4" hole in the middle. Any thoughts? Thanks!

BTW, I'm devoting the following week, my college spring break, to my bike - so you'll probably be hearing a lot more from me in the next few days. This is what I'm doing while my friends are busy getting black-out drunk in places much warmer than Michigan... but it'll pay off when it starts getting warmer.

Anyways, I'll try to combine questions and keep posts to a minimum. In that spirit, is it possible to perform float height tests on these bikes with the carbs installed on the bike? How would you attach the hose to the float bowl, when the openings are plugged up with bolts? replace the bolts with tube nipples, perhaps?

Thanks again,

Marshall

[marshall]

whoops, here's the photo:

[DGXSER]

Hello

Hey Marshall, Welcome to the board!

The later model carbs on my 81 special have a bit of a different setup on the float bowl drains. The drain screw comes in from the side and the drain itself is vertical. So you could easily attach a hose to the drain and work the drain screw. I think that is the reason they added this test method for the later models.

It soulds like you may have an early 80 model or replacement carbs of the earlier model, either way, not condusive to the on bike float level test.

As to the hole in the air box, I am not sure, I have heard of some members drilling holes in the air box to let the beast breath easier. IIRC, the airflow comes in the middle of the filter and out , so the hole you describe should still be filtered.

[red bandit]

#50-51 it's like a stone screen to drain any gas I believe. If yours has a hole clean through it your either missing the stone part or someone put a hole in it.
If you have a bolt in the bottom of your carb bowl you would have to make a nipple that screws in to do a fuel level test.

[marshall]

Thanks DGXSER,

Your float bowl drain arrangement is what I'm used to; maybe my older setup just isn't meant for on-bike testing (which is fine with me, actually!).

The picture is actually a little deceiving; the hole is in fact in the post-filter part of the air box, so air getting sucked in there is not filtered, and goes straight to the carburettors. I found a different sort of surprise on the filtered side when I was taking it apart - a wasp's nest clogging up nearly the entire intake tube! Second time I've had wasps move into a motorcycle - lots of good hiding places. I wonder how long I was riding the bike with that thing in there...

[marshall]

#50-51 it's like a stone screen to drain any gas I believe. If yours has a hole clean through it your either missing the stone part or someone put a hole in it.
If you have a bolt in the bottom of your carb bowl you would have to make a nipple that screws in to do a fuel level test.

Ah, that makes sense. I pulled my cap (51) off and there's a cube-shaped opening there, perfect for a small filter. I suppose I'm actually missing part #50, which I thought was just the protrusion on the box. I think I can cut a chunk of foam to fill the void and filter the air coming in, but the question is whether the original filter/stone screen was very breathable or not. It could let a fair amount of air in when the engine is running, or it could let very little air in and only drain gas slowly when necessary. Can you give me an idea of how breathable it is? Thanks!

[TopCatGr58]

Hey Marshall,

It's a simple screen type filter, just to keep bugs out and let gas out when the carbs overflow! But you're right, it is on the unfiltered side of the cleaner. As was mentioned, folks have drilled several holes thru the section that coincides with the INSIDE edge of the filter contact area to provide more unrestricted air flow vs. just the SNORKEL. With the OEM airbox, you still get the velocity stack affect of the air going into the carbs, so the holes in the airbox don't affect the tuning very much!

If you go thru the tech tips, the misc. section, you'll find a serial number listing where you can check yours against to verify if you have the 80 or 81, which would be very important with regards to tech suggestions and such, since they use totally different TCI's for example. The 81MNS also has the Swirly spoked rims, linked right front and rear brakes, etc.!
T.C.

[Ken Talbot]

Yes, there should be a bit of foam keeping bugs out of the drain hole in the airbox. Ideally, all they should ever come out of there is a bit of moisture, or a bit of oil if you get a bit over exuberant when oiling the air filter element.

[CatatonicBug]

In mine, that cap was literally melted over by the PO. Mine seems to drain extra air filter oil and condesation just fine out the side of the airbox when the bike is on the side stand.

I too had several wasp nests in mine when I first got it. That encouraged me to get really serious with cleaning all the nooks and crannies!

[Shappers]

The filter on mine just fell apart in my hands when stripping the airbox.

I ended up just snipping a square piece of yellow dishwash sponge and fitting that in there. You should have seen the wifes face the next time she picked her sponge up