Topic: 1973 CB500: mysterious water vapor

[keelhaul]

My bike is actually missing both the crankcase breather and the airbox breather, but the airbox breather is still stocked on Bikebandit, etc so I'm okay there. The crankcase breather hose is discontinued, however. What can I use as a replacement? UNI makes a breather filter, is that something I can attach directly to the crankcase nipple or should I get a hose and route it under the bike?

A secondary, possibly related question- after running it around the neighborhood for about a half hour I get a moderate volume of white vapor that appears to be coming from the top of the carbs. Is this related to the missing breathers? I don't think it's anything to worry about but I figure it's best to ask the experts. I live in a dry climate (desert north of Los Angeles) and it hasn't rained here in forever, this seems like a lot of vapor. I read that there are supposed to be vents on the mufflers to help manage condensation in the exhaust, if those were clogged could the vapor gas out of the carbs instead? I think I've located the vents on the exhaust, the tiny holes on the bottom- can I just ream them out with a piece of wire or will I damage something if I go rooting around in there with a paper clip?

EDIT: retitled the thread since now I know the (lack of) breather tubes aren't causing me any trouble.

[Deltarider]

Originally the 500 came without a connection between the breather tube and the airfilterbox. There wasn't even a breather filter. Don't be tempted to fit one as these devices, even on the 550, are known to foul and wetten the paper airfilter element. TT will argue that people should service the breather filters and tubes more regularly, but I know dealers and riders here simply disconnected the breather filter and rerouted the breather tube as shown on p 170 of the Honda Shop Manual. By doing this they could continue to use the genuine paper Honda filter element and did not have to turn to foam filters that are inferior in filtering particles. It's your choice.

[keelhaul]

I'll stick to the stock setup, then. Got any suggestions on what I can use as a crankcase breather hose? I'm sure my stock of Lowes brand vinyl tubing is not up to the task.

Is this causing the volume of water vapor I've been seeing?

[Duanob]

NAPA has rubber vaccum line that works perfect. I forgot what diameter it takes but it should be too hard to figure out. Measure the crank breather tube that comes out of the cover. Where it's connected to the airbox is below the filter so moisture shoudl get trapped there instead of inside the paper element, ulless you have a big blow-by problem. I rebuilt my airbox element filter the fits in the bottom with steel wool. The inside of the paper element looks like new but the outside needs cleaning. They way it should be if everything is working properly.

[keelhaul]

Looks like I'll be swinging by NAPA on the way home for some 3/16 vacuum line and a cable clamp, thanks for the tip!

I'll have to inspect my filter when I get home, I know the outside looks dirtier than the inside but I figure I have to be pulling air in through the breather nipple without that breather assembly, correct? Is there a valve or something on the OEM breather tube that prevents the airbox from sucking air in since it's not connected to the crankcase breather like on the CB550s?

[keelhaul]

Quick update: I plugged up the airbox breather temporarily with duct tape and took the bike around the block to see if that was the source of the water vapor- it's not. It's definitely coming from somewhere on the right side of the gas tank up near the seat (it blows down right on top of the carbs). Is there another breather hose up there that's just not plumbed correctly (like all the other breather hoses on my bike) or is something more serious going on?

Working long hours means I only get about a half hour a day to tinker with the bike before I have to shut it down so the wife can go to sleep. Tonight's job: testing the front stop switch with a multimeter to figure out why my brake light only goes on when I hit the rear brake. Taking the tank off the bike to track down the source of the water vapor is going to have to wait until I have the hoses and stuff I need to drain the gas tank.

[spot45]

Just out of curiousity what is your bike's history?  Did it sit for a number of years before you found it?  How often is this white vapor coming out?  After reading some of the updates in the CB500 Tech manuals I may have an idea as to what that white vapor is.  It is not water vapor, it is fuel.  The CB500K has a history of having valves that will stick.  They did say how to fix it in the dealer set up manual, additions.  I believe the same problem is happening with your bike, as I had a similiar problem that happened with mine.  The only solution would be to do what they tell you to do in the dealer supplement.  But I will add this bit of advice spray them with Marvel Mystery oil, Seafoam doesn't work as well.

[keelhaul]

I bought the bike off a garage that restores them, mine originally came from Michigan. They replaced the fuel lines, brake lines, throttle cable, cleaned up the carbs, replaced the brake pads/shoes/fluid, etc. I'm not sure if it had been sitting before they bought it and fixed it up but it definitely hasn't been sitting since then.

The white vapor only starts flowing after I've ridden the bike for 20 minutes or so. It comes out from under the gas tank on the right side of the bike near the seat. It doesn't smell like fuel, I stuck my face in there and got a good whiff (and almost a good burn!). It's quite light and fluffy and disperses easily, which is why it was so tricky to track down. It sort of "puffs" out in jets (as opposed to leaking out in a diffuse fashion), like it's being run through a nozzle that I can't quite see.

[domer]

so here is where the breather hose goes. this pic is from the carb side of the motor. Mine just routes down  in front of the back tire. i blow steam on hot days puttin around the city. Never really looked into why, as its only happened 2-3 times over the past 3 years. now I'm curious 
 

[keelhaul]

I'm reasonably sure the steam isn't venting from the crankcase breather, I spent a good 10 minutes yesterday tracing the source with a piece of cardboard and a flashlight, it's definitely coming from under the tank towards the seat. I'm going to pull the tank off tomorrow and have a look, I spent all my bike-tinkering time tonight tracking down a bad front stop switch connection.

But hey, I fixed an intermittent problem with my right front turn signal while I was poking around the rat's nest inside the headlight bowl, so it was time well spent

[dave500]

if you do a lot of short runs around town and dont really get it hot or into the power for extended periods water can accumulate as a normal by product of combustion and settle in the oil,the steam you see out of the breather is most likely oil mist with a little water vapour,,youll see more water vapour from the actual exhaust outlets when your warming the bike up,hold you palm over the exhaust a few inches away within the first minute or two of starting the bike and water will settle on it,try it after the bike has been fully run and well hot,itll be dry, it has turned to steam and you cant see it.

[Duanob]

Just curious if you've taken the tank off the bike yet? At least you will know what's underneath it. Not sure where steam could be coming from under the tank except for the breather tube.

[keelhaul]

I lifted the tank off a bit on my way out the door this morning to see if maybe there's a mystery tube down there, but no. When I was tracking the source of the vapor I put a piece of cardboard over the crankcase breather to block it, but it didn't affect the flow of vapor. I'm going to double-check tonight, if it's not coming from the crankcase breather then I'm stumped.

Could it be coming from where the fuel lines meet the tank? Seems farfetched to me but I've been wrong about this bike before (plenty of times!).

Extra thanks to dave500, I didn't catch any moisture with his hold-your-hand-behind-the-exhaust-outlet trick but I did find a pretty big hole in one of the mufflers when I noticed it wasn't "pushing" as hard as the other 3!

[domer]

there shouldn't be anywhere that vapor could come from besides the crankcase breather. maybe the breather is clogged (slightly common) and its forcing out a weak spot in a gasket? i think id expect oil with that though. same would go with a crack in something... or maybe they put the cover that the crankcase breather attaches to on with out a gasket, i don't remember how much oil gets up there... i think its little to none though, could be wrong.

there are also 2 hoses that attach to the carbs and and route down to the wheel also. don't know what the hell they are for but i don't think that's your problem.

on a side note i figured out the vapor from mine is gas  kind of expected that since the carbs will spew a whole tank in a matter of hours when i forget to turn it off.

[Danno]

those two hoses are the float bowl breather tubes the side you describe is the battery side check to see if you have a tube on the battery if it is fumes from the battery because it is over full or because you are in the desert get it fixed quick those fume can be ignited if it is the battery

[dave500]

if was battery fumes that bad youd smell rotten eggs,that hydrogen gas is explosive,,not just ignite and burn it does explode.

[strynboen]

if not use the air filter brether...close the hole in filter element in bottom...then no air goes between the filter and housing..mine are a 550..not shure ab 500 are same