Thread: carbon canister on a GM vented gas tank

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I have a 35 Chevy with a stock gas tank. When I park it in my garage I can smell the gas vapors from the gas cap. I installed a carbon canister connected to my carb. I have the solenoid connected to the brake light. When I step on the brake the vapor is pulled out of the canister. If I drive on the highway for awhile no vapor is drawn out so I can get into a vapor lock situation in the carb. I remove the cap and I can go again. The vent is blocked on the gas cap. Should I have the solenoid open all the time when the engine is running, or should I install a vented cap to break the vapor lock? Has anyone had this issue before?

I hate vented caps, hard to find one that actually works the way it's suppose to. I normally run a vent line off the gas filler tube up into the highest spot in the trunk & then back out of the trunk WITH a fuel filter on it to keel any dirt out that might be sucked in as the tank expands & contracts....you

Originally Posted by russ35

I have a 35 Chevy with a stock gas tank. When I park it in my garage I can smell the gas vapors from the gas cap. I installed a carbon canister connected to my carb. I have the solenoid connected to the brake light. When I step on the brake the vapor is pulled out of the canister. If I drive on the highway for awhile no vapor is drawn out so I can get into a vapor lock situation in the carb. I remove the cap and I can go again. The vent is blocked on the gas cap. Should I have the solenoid open all the time when the engine is running, or should I install a vented cap to break the vapor lock? Has anyone had this issue before?

Something doesn't add up. You start out by saying that you can smell gas at the cap while it's parked in the garage, but then say it isn't vented going down the highway. As far as I know, caps are or aren't vented. Can't do both. So I'm wondering if the fumes are actually from somewhere else.?.? And I can't say that I've seen or heard of the use of a brake activated solenoid to purge a carbon canister.... how did you come up with the idea?

I agree with Joe & Mike, leave the cap alone but install a tank vent with high siphon/loop to start. OEM vapor systems have the tank vent line running to a vapor/liquid separator that drains back to the tank, the line to the canister, and then the control valve which the ECM drives. I think that the canister is being purged anytime the engine runs, to suck absorbed fumes out of the charcoal. Venting it only when on the brake doesn't seem like a good idea.

Sorry for the confusion. The cap was originally vented. Because I had this odor problem I had a guy install the carbon filter. This filter set up needs to be re-designed. They connected the solenoid to the brake wire that opens the vacuum line from the carb to draw out the vapors. I now have a non-vented cap (plugged with some rubber) with a canister and a vacuum line to the carb. The vapor line comes off the tank neck to the canister. Any ideas how this could work?

This sound simple to install. Do you get a gas smell when the car is parked in a garage? That is the only thing I am trying to resolve.

Did it ever work as designed ? If it did and now its not I would bet your solenoid shot craps. And if its wired to energize with the brake lights you are probably not purging the canister long enough,plus running rich @ stops. Most canister systems purge when the engine is cold so as not to cause any warm engine richness. The early systems used a simple temperature vacuum switch that screwed into a coolant port @ the intake manifold,normally open (purging) until engine hits 180 or so.

No, this idea came from a local Hot Rod shop. It never did work right. I think I will use a high point vent through a filter and see if that works. This would be TooMany2count's idea.