Have you checked your sub air cleaner lately?

Have you checked your sub air cleaner lately (4th Gen.)?

I had what I suspected was a stuck float - gas leaking under the bike when parked overnight, a big backfire and a terrible "rich" condition when it started. It wouldn't turn over until I put it in 6th gear and rocked the engine backwards a little (hydraulic lock possibly). After 20 minutes of running a little rough, it seems to be OK.

Anyways, I had the panels and tank off and came across this little filter - from what I can find out it's a vent for the floats or carb diagrams. Mine was totally disintegrated, maybe 10% of the foam element left. Not sure if this caused my problems but it may be something people should check next time you have your tank off..

Cheers

 

That looks an awful lot like a PCV Filter.
(Positive Crankcase Ventilation - vents the blow-by gases from the crankcase, but traps suspended oil and other particulate matter).
After the filter element, the gases are supposed to go back into the air-cleaner to be recycled back into the engine to minimize pollutants/smog.

All modern motorcycle & auto engines have had PCV systems since the early 1970's, or earlier.

Whether it's a PCV vent filter, or some sort of carb/float-bowl vent (not unheard, esp. knowing Honda), you can probably just leave the large hose open to vent to the atmosphere

I bought my bike Used/Salvage, and immediately found that hose open - The filter was AWOL.
I've left mine open until the next chance I get to buy a PCV filter and feel like taking the tank off again.

Any automotive parts store will sell a variety of PCV filters that would work, or you can get a fancy little K&N-type filter for more $$.

To address your issue - I'd be surprised if that would have any adverse affect on running quality/carburetion.
If anything, an engine would run better and make (slightly) more power ingesting only clean air without also having to breathe the blow-by gases.

I suspect your issue is not related, just coincidental.

 

Thanks Rat.

I did some more research and I'm thinking diaphram vent. It is to supply atmospheric pressure. It enters the top of the carbs. The tube has it's own horizonal filter and not connected to the air box so it's not affected by changes in vacuum. Anyways, I ordered one of the filters($4) and we will go from there. You can see from my pictures it looks like my float vent has spewed a little gas lately.

I had it running for awhile last night - sounds good, no leaks or gas smell. I think I had a little piece of shit holding up a float valve.

 

You're welcome, although I don't think I really helped much, other than "don't worry about it"!

I had my tank off briefly just to replace the air filter and change the rear spark plugs.
I noticed the hose, but didn't really pay much attention, as my mind simply registered "PCV hose - don't worry about it", and buttoned it back up when I was done.
I don't recall seeing a 'Sub Air Filter', but I'll look again.

By your excellent photos, it does indeed appear to be a carb vent, as the PCV clearly goes directly into the airbox (at least I had that much right!).

Now I think I'll take things apart again and run cheapo PCV filters on both the carb vent and PCV hose so the blowby gases vent to atmosphere.
I've done that (PCV filter) with practically every bike I've owned - who wants their engine breathing other than pure air & fresh fuel?

The diagram pic does not seem to show any vacuum source or even outlet for the fuel fumes downstream from the filter element.
Is there an Outlet to the little box?

I was thinking to just run the carb vent into the airbox PCV inlet, but I'd be worried about high-RPM airbox/intake vacuum robbing the float-bowls, exactly what you DON'T want!

Thanks for bringing this to everyone's attention!
Cheap and necessary Mod, as far as I'm concerned.

 

The box is open at the bottom, when my filter arrives, I'll take a picture of it and post.

Most of the info I could find on carb diaphram venting was in aircraft. The point seemed to be you don't want it facing forward or aft because of the effects of airspeed. (or land speed in the case of our viffers!)

 

OK, I wasn't getting it.
(I was enjoying a fine Single Malt last night...)

It appears the "Sub Air" filter/hose is an Intake for something - why else would it need its filter to be cleaned & oiled?
But what?
Would the diaphragm chambers need filtered air?
I don't believe I've ever heard of that.

My curiosity is killing me - Now I need to go out and tear everything apart to finger it out!

Clearly the Sub Air hose can simply be left open, if not "optimum" without a filter.

So, where does the end of the Float Vent hose connect?
Anything?
It looks like it's simply resting against the valve cover.

Aargh!
I can't just leave this stuff alone!
I gotta get out there tomorrow and tear into it, and make it 'perfect'! :biggrin:
I have a long ride planned for Sunday, and this would haunt me if I knew it wasn't set up right...

 

I hope I didn't ruin your weekend, buddy (by opening "a can of worms")!

The tube I'm calling the float vent is open. I think it would only "blow". I'm thinking the diaphram vent would ebb and flow a little one way then the other - hence the filter. I'm no mechanic - so please correct me if I've got it ass-backwards.

Hoping the weather clears up later today for a test ride.:smile:

 

Just to close this thread out and draw attention to "something to keep an eye on"...I found my tank vent was blocked. This must have caused the expanded fuel pressure from the engine heat to force its way into the carbs after it was shut down. It only happened after I was stuck in traffic on a hot day for an hour and shut it off right afterward. I had noticed some pressure / vacuum in the tank when I opened it before. I managed to blow the vent pipe in the tank clear with compressed air (took about 60 PSI). I changed the oil just in case it was gas contaminated. Seems fine now.