Gas cap pressure/charcoal canister

poptop tom

Here's the situation:

I have a 76 FI 2.0 with an engine I finished rebuilding late last fall. I proceeded to drove the westy to Florida three days after engine install and break-in. Other than a faulty ignition switch (and a few minor bugs to work out) in the middle of BFE Kentucky at 2 a.m., the bus and engine ran great.
One of those "minor" bugs is the gas cap pressure when removing the cap to fill up. LOTS of pressure built up each time.

After reading many searched posts on the subject, I can't seem to come to any conclusions.

As part of my bus restoration, here is what had been done previous to the engine build. At least what might be pertinent to this discussion.
1) all new fuel and vapor lines replaced per kits sold by German Supply. Including the rubber line up in the air vent area behind the spare tire well.
2) Por-15 treatment of gas tank.
3) new fuel filler neck.
4) all vapor and vaccuum lines hooked up correctly, as well as the charcoal canister and associated lines coming in and heading out.

The 76 has the charcoal canister towards the front of the engine compartment. I removed it, plugged the small line with my thumb, and blew through the large port. So dusty charcoal material came out each time, but I could blow freely through the canister.
The gas cap is a locking, non venting cap. It is very tight to twist on and off, and even without the pressure.
I removed the few vapor lines at the back of the engine compartment (where the tee is) and can blow air freely through these lines as well.

Any advice on how to proceed? Thanks!
_________________
'76 Deluxe Campmobile

busdaddy · Posted: Sat Apr 09, 2011 8:16 am Post subject:

How about the small line on the canister, can you blow through that?
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SGKent · Posted: Sat Apr 09, 2011 1:08 pm Post subject:

there are two metal lines coming down from the side air vents that bend and come to the center near the engine bay door. They should be hooked into a 3-way Tee at that point and a small hose to the canister comes off that 3-way Tee. Is yours hooked up that way?
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

poptop tom · Posted: Sun Apr 10, 2011 8:47 am Post subject:

poptop tom · Posted: Thu Apr 28, 2011 8:30 am Post subject:

Ok. I still need guidance.

While continuing my alternator red light troubleshooting, and knowing I'll probably have to pull the alt., I decide to run the bus for 10 minutes here inside the shop. I wanted to do this to see if removing all the vent lines from charcoal canister allowed the gas tank to properly relive itself of the built up pressure.

Well, I still have built up pressure at the gas cap. Engine compartment vent lines are disconnected.

Now what? Pull the damn engine to find out if its back there around the tank area that is giving me issues? I dont see where the problem could be at this point.

Could the bulbed deal up in the air vent be plugged with crude on both sides?

Pulling my hair out.......
_________________
'76 Deluxe Campmobile

busdaddy · Posted: Thu Apr 28, 2011 8:38 am Post subject:

If you remove the short rubber hose on the left side between the spare well and outer 1/4 panel (red coded hose on Ratwells diagram) you can connect a long hose directly to the tank vent and bypass the condensor bulb for a test. You could also try blowing into the bulb tube to check for restrictions and possibly ream them all out with mechanics wire.
(That hose is easy to access with the LH tail light removed BTW)
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poptop tom · Posted: Thu Apr 28, 2011 9:05 am Post subject:

MOX · Posted: Thu Apr 28, 2011 9:54 am Post subject:

brilliant!
(That hose is easy to access with the LH tail light removed BTW)
Cool

i wish i had thought of that 2 years ago in temagami ontario after getting gas and it started leeking out of that damn little "red" hose.....ha ha ha

busdaddy · Posted: Thu Apr 28, 2011 10:17 am Post subject:

No it's very uncommon for the bulbs to plug but anythings possible.
I'd start with something like a clutch cable in a drill if it'll fit in the pipe (you may have to find some smaller cable at Home depot), the RH one is going to be more difficult as you'll have to cut the tube and rejoin it after like the LH one with a short piece of hose.
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Rust NEVER sleeps and stock never goes out of style.

Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
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poptop tom · Posted: Thu Apr 28, 2011 10:23 am Post subject:

Thanks BD. Apparently I asked some questions 5 + years on the subject......

and a response from Colin was this....
"The bulbous things are vapor separators just like on hydronic heating systems. If you up-chuck you will ruin it's function. Where are you attempting to establish that the line is clear? At the tank upstream of the separators, or from the engine compartment going towards the tank via the separators? I would do some goofy thing like getting some fuel hose and clamping it to the line along the ceiling of the engine compartment at the bottom of the air scoop. Curl it upwards so that it is higher than the separator. Spray some GumOut down the fuel line so that there is a small pool of GumOut at the bottom of the loop. Blow into the hose to see if you can drive GumOut into the separator. Try this from the tank side too. Keep us updated. Observe all safety precautions. Do not drink GumOut"

So if I blow air back through the separators toward the tank I will ruin them? What exactly is inside on these that will get ruined?
_________________
'76 Deluxe Campmobile

busdaddy · Posted: Thu Apr 28, 2011 10:38 am Post subject:

SGKent · Posted: Thu Apr 28, 2011 10:54 am Post subject:

I believe they are expansion chambers to help catch any liquid. The reason you don't want to blow backwards is that any rust or debris will end up back in the tank.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

poptop tom · Posted: Thu Apr 28, 2011 10:55 am Post subject:

poptop tom · Posted: Thu Apr 28, 2011 10:58 am Post subject:

poptop tom · Posted: Fri Apr 29, 2011 7:21 am Post subject:

Got the problem solved! I ended up with two major clogs (solidified dirt it seemed like) on each side of the system - the two steel lines that go down into the engine compartment from the separators. The passenger side I was able to ream braided wire (smaller then larger size) through the jam to free it. Then I vaccuumed it out as much as I could.
The left was another story. Its jam was at the end of the line in the engine compartment, right at the 90 degree bend. I ended up having to sawz-all a 10" chunk of the line out. Then used a cut section of straight coat hanger in a cordless drill.
I was then able to blow forced air freely through the line. I disconnected the rubber hose in the left wheel well area, hooked a section of tubing onto it, and forced the air through in the direction of the compartment.

I guess I may go ahead and find some charcoal for the canister while its out.

Busdaddy, thanks for the offer to cut one of those separators in half for me. No need now. But my curiousity has got the best as far as finding out what the heck is inside of there!

One final question: Which direction does the air flow through this vent system? I have the bus running right now, and the lines in the engine compartment seem like they are sucking the air back up through the separators towards the tank.
_________________
'76 Deluxe Campmobile

busdaddy · Posted: Fri Apr 29, 2011 7:47 am Post subject:

Excellent news, could the blockage have been from mud daubers or other insects that moved in when the lines were open?
I'm still curious about whats in the bulbs, I'm still opening one up but I'll do it at my leisure, one thing I noticed yesterday was VW attaches them to the bus with a bead of weld up the side so whatever's in there isn't damaged by heat.

There is no one way only they flow, when the level of gas or temperature in the tank drops air will be sucked in, if the tank warms or gets agitated they'll flow away from the tank.
_________________
Rust NEVER sleeps and stock never goes out of style.

Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
Stop dead photo links! Post your photos to The Samba Gallery!

Слава Україні!

poptop tom · Posted: Fri Apr 29, 2011 7:52 am Post subject:


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