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I give in: how does the EVAP work?

sqeeezy

Well travelled
Location
Southern Spain
Not too hot today so I went for a blat up the other mountain and back home again.

Inspired by reading stuff about EVAP on the other forum, and feeling guilty cos I hadn't checked it since I dumped it in red clay mud in Morocco, I dropped the sump guard and had a look at the mess of tubes and stuff, with a view to cleaning it up, removing insect cocoons and generally getting my head round how it works. I'm a tree-hugger and I like this planet (Hell, it's the only one with bacon and chocolate on it! ) so I'm into clean air for my kids and their kids etc., so I'm not going to rip it off just because I can't understand it.

So..no mud found, no insect cocoons,
blew threw tubes and t-piece ok,
blew through petrol tank vent line with tank open and then with tank shut (verifies tank cap seals ok and gives you a funny feeling in your ear),
blew through purge valve from petrol tank vent connector to canister loopback hose connector and got it to open with a slight jokey trumpeting note (the 3rd line on the purge valve reacts to suck and blow as if there's a small diaphragm-like movement inside, but no air flow).

So the charcoal canister is venting to the air of my favourite planet with the short siphon shaped hose stub; what's that about?:
all three lines on the canister freely communicate with each other...odd...
The throttle body line connects to the T-piece, yeah?,
and the T-piece connects to the canister,
so how can the throttle body vacuum open the purge valve if it's able to suck fresh air in via the T-piece/canister/canister air vent.
Isn't that like "short-circuiting" the vacuum?
I'm obviously missing something.

I'll paste the bit from the BS4 Vehicle Service Manual which could profit from a native English-speaking proof reading. Here for what it's worth:

The purge valve is a mechanically controlled one way valve. When the engine is off, the purge valve is closed. When the engine is started, the vacuum created in the suction port is used to open this one way valve and allow the vapors to go into the inlet port.
The Evaporative emission control system EVAP fitted in our motorcycles prevents gasoline vapors from escaping into the atmosphere from the fuel tank.
As soon as the motorcycle is parked after riding or parked under the sun, the hot radiation from the engine / sunlight causes the fuel in the tank to warm up and releases fuel vapors.
The EVAP system prevents these fuel vapors recycled to engine to avoid vapor into the atmosphere and stored in a charcoal canister.
As soon as the engine is started. these vapours are purged from the canister, into the combustion chamber. The system consists of a canister, purge valve, rubber hoses, connectors and a sealed fuel tank cap.

To put it in perspective: I love the bike: it gives me chewing-gum jaw from grinning too much. This EVAP stuff is just me trying to understand it: I'm not whingeing.

Happy Trails, team!
 

CarstenB

Well travelled
Location
h-town tx
i've wondered the same and am no wiser than you. Question is what does that snorkel do? The other two openings are vapor in and vapor out but that snorkel i have no clue. It can't be that it is open to the evap system otherwise the engine would suck unfilter air and indeed would render the entier thing useless. I can only imagine that it is connected to some sort of expansion chamber but not to the charcoal. Or there's an overpressure valve in the canister that allows it to vent if needed. No idea. Someone has to cut the canister open i guess.

Here's a good writeup with photos


Screenshot 2019-08-26 at 5.32.56 PM (1).png
 

sqeeezy

Well travelled
Location
Southern Spain
Question is what does that snorkel do? The other two openings are vapor in and vapor out but that snorkel i have no clue. It can't be that it is open to the evap system otherwise the engine would suck unfilter air and indeed would render the entier thing useless.
Thanks... but I checked mine and all 3 connections to the canister breathe to each other, if you know what I mean. No resistance to my blowing in any of them. Is my canister faulty? Try yours and see what yours is like. Ditto anybody else that's interested. My bike starts and runs well, albeit a tendency to stall when cold after a while on a closed throttle.
I've seen the bhp stuff, it's still a bit light on science, although the guy's re-routing recommendation may be useful.
EDIT: I've just fired off a tweet to RE: who know, I might get an explanation of EVAP functionality from them...fingers crossed..
 
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NewEnglandHimalayan

Well travelled
Location
New England
I personally don't know what that "snorkel" is. Also, I suspect that you are not finding resistance from blowing into the hoses because maybe your ignition switch is off and/or the engine is not running. There is a chance that these things have electric valves that rest in a particular state. As for guessing what that snorkel does, I would dare to guess that it may be the intake of their version of the AIR pump in cars. In cars, there is a pump that injects clean air into the intake on cold starts. This is done to achieve some emissions standards. In cars however, this hose is attached to the air box in that it would be sucking clean air. The position of the "snorkel" however, tells me that it may be simply a vent. Who knows. This goes to prove I know nothing LOL. Ride on!
 

sqeeezy

Well travelled
Location
Southern Spain
I personally don't know what that "snorkel" is. Also, I suspect that you are not finding resistance from blowing into the hoses because maybe your ignition switch is off and/or the engine is not running. There is a chance that these things have electric valves that rest in a particular state. As for guessing what that snorkel does, I would dare to guess that it may be the intake of their version of the AIR pump in cars. In cars, there is a pump that injects clean air into the intake on cold starts. This is done to achieve some emissions standards. In cars however, this hose is attached to the air box in that it would be sucking clean air. The position of the "snorkel" however, tells me that it may be simply a vent. Who knows. This goes to prove I know nothing LOL. Ride on!
Ahem...Hello...well there aren't any electric valves: the purge valve is pneumatic; it's a check valve actuated by the throttle body manifold vacuum. I've been seeing what Google can come up with, and frankly I could probably write a better search engine on the back of an envelope, it gives you loads of results really quickly but none of them actually match your search parameters..anyhow the snorkel, which looks different in the manual, BTW, is so that fresh air can flow in (and water, too if you're crossing a ford at the time) to displace the petrol vapours sucked out from the activated charcoal (about $10/kg on Amazon). I'll have to go back and try another blow test, or maybe .. eek! .. a suck test to see if there are check valves in the canister, cos car systems usually have them. No worries, it's all Goodman, sleep is not being lost nor trails untrod due to this, it's just irksome for me to have to reverse-engineer stuff when the manufacturer is still alive. Triumph's not much better, they didn't tell me the map for my Bonnie was obsolete, I found it on the forums: they just want to sell us stuff, and there it ends.
 
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