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V7 Classic fuel venting puzzle SOLVED!!!

Alan L in BC

Alan L in BC

Tuned and Synch'ed
Joined
Feb 15, 2010
Messages
34
I have recently removed the evap system - plugged vaccum ports, airbox hole, and run the two hoses from the bottom of the tank down and out of the way, with no kinks or blockages. After riding the bike (tank half full) and shutting it off, 4 or 5 drips of fuel come out of the larger "tank vent" hose, the one that starts at the fitting to the right of the filler hole in the tank and attaches under the tank at the rear fitting. (first pic) I guess that this fuel originally went to the cannister. This dripping happens consistently, so it isn't just a one-time occurance.


What seens to me to be missing is any kind of seal underneath the cone-shaped alloy part. (second pic) I can't see any reason for fuel not to slosh up between the plastic of the tank and under the metal part, thus always resulting in dripping of fuel out of the hose. I always wonder about things that are designed as they are which seem wrong to me - see my thread about centerstands from a few weeks ago - and I want the tank to vent air, not fuel.

I searched the small-block forum and I could not find any info on the tank venting system that was any help

Has anyone else without the evap system in place come across this dripping of fuel?

Thanks
 
Re: V7 Classic fuel venting puzzle

Hi Alan,

Sounds like your tank is behaving as it should. You have the details right in what routes where; the aft barbed fitting is the tank vent, and it originally runs to the evap canister. The foremost barbed fitting is a drain line from the gas cap ring, it drains any fuel or water that collects in the cap surround. On the NA tanks, air to replace fuel has to vent in from below; in from the evap canister, up the hose, past a check valve (the one that's the subject of the current upgrade), then into the tank from the hole in the filler neck in your first picture.

When the tank is very full, of course fuel is likely (certainly) going to slosh up into the hole. There's really no way around it, as that hole has to vent to atmosphere in order for the tank not to suck itself to death. The check valve is there to prevent this fuel from running out of the bike; it vents both ways, and takes a certain level of pressure to open. More so outwardly than inwardly - which is why the check valve is directonal. So a very slight negative pressure is maintained while the fuel pump is running, which keeps the line clear in normal use, and any excess collects in the evap can which eventually gets sucked back into the throttle bodies. However, if the evap can is removed, any fuel which does make it past the check valve, or which collects in the line and then gets purged out when the tank needs to burp (ie, on a recently parked hot bike) will drain to the ground. If the check valve is removed entirely during an evap - ectomy, fuel has an uninterrupted path from that hole to the ground via the internal and external tank venting.

A few spots on the ground after parking the bike are totally normal when evap can-less, there's just nowhere else for the tiny amounts of blow - by fuel to go. Euro bikes lack the evap emissions system and don't have the same issue, as they vent through the cap. In fact they don't even have the aft barbed fitting installed in the tank, just the front one. A collary to that though would be to be sure to not put a US cap on a euro tank! IE when perhaps installing a chrome tank on a USA model V7 Racer... to not also order the euro cap would leave your tank with no venting...

Guzzi can probably be forgiven for this one, it's an annoyance of the California required evap emission system; euro bikes can vent tanks directly to the atmosphere through the cap, US bikes can't. The best US bike evap removal practice includes putting a solid bolt in that aft tank vent fitting to replace the hose barb, and ordering a euro - spec cap to vent through; no dripping, no check valve, no venting issues.
 
OOOH, I love to be right!!! I cut a 1/16" thick cork gasket and put it in between the alloy cone and the plastic of the tank. No more drips, with the tank filled right up, after 4 or 5 short rides. The alloy cone has a small vent hole on it's top, so the tank still vents, but the fuel can't slosh under the cone as it was before. No tank pressure, of course. Hem hem.
 
Going to remove the EVAP on my 2013 V7 Stone, single throttle body.. Do the new V7s have the same problem as the older ones described here? I read that I just have to plug the line to the intake and leave the one to the gas tank open. And also make sure I remove some sort of tip over valve (not sure what that is exactly as I haven't attempted it yet.)

Also, do you still have pics that were there before…they're no longer visible. I'd like to see what you did with the alloy cone and gasket.
 
Thanks for the reply. Yea, I've been going back and forth about removing it or not. Probably not necessary to do so but it also seems like an unnecessary piece to have on the bike anyway. Thanks for the help though.
 
The Zard silencers in put on mine certainly helped ride-off time. It takes less than half the time it did with the stock silencers. I can usually drive off in under a minute. One less thing to annoy me!
Bare
 
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