Hey Guys, I've got a 74 F100 chassis with a 77 351M in it. The hose from my charcoal canister to the motor is missing. The line from the gas tank is there. According to my Haynes repair manual it goes to the vent on the carb's fuel bowl vent. My carb doesn't have one. Would it be OK to connect it to the air cleaner? It's a after market chrome air cleaner with a plug on the underside for a breather hose of some kind. I kinda figure it's for a crank case breather hose. I've got a functioning PCV valve on the right side and a breather cap on the left side valve cover. Any input is greatly needed, I'm tired of the fumes under the hood.
Thanks in advance
Mark

 

I believe I would remove it and plug the line the line that goes to the tank. It's supposed to vent the carb.

1977 Ford F-100
400m/c6
280,000 miles
Stock on the outside
modified/rebuilt everything

 

I guess it depends on your conscience. It sounds like it just has two hoses and no purge valve on it right? Pull the hose off and just cap the port on the canister. I'll check and see what kind of purge it should use if you'd like to minimize the vapors from your tank.

 

Tetraruby is right it vents the tank throught the carb. I think when you first start the engine. If you have a different carb and don't have a vacuum fitting to hook to it cannot work. I don't recall if it uses ported or straight cacuum.

1977 Ford F-100
400m/c6
280,000 miles
Stock on the outside
modified/rebuilt everything

 

Tetraruby, Yes it only has two lines on it. I'll probably just go ahead and plug. Let me know what you find out. Thanks for clearing this up for me everyone. I was just gonna run it into the air cleaner. Glad I posted here and got straightened out.
Mark

 

My 74 vents the canister to the air cleaner. I've seen chrysler cars that vent straight to the carb, but what does it matter? it's two solutions to the same requirement. If your air cleaner has a vent fitting on it, use it! the idea is to have engine vacume pull the fuel vapors into the intake. It makes absolutely no difference if the vacume source is the air cleaner, or carb. Whatever you do, don't just plug off the line that goes to the tank. Older systems had vented tanks, the later were vented to the canister. If the tank can't equalize pressure, you'll have all kinds of strange problems.

 

just my .02 cents worth but I think you have to have a vauum source which would be under the carb. There wont be any vacuum to speak of inside the air cleaner unless it's very dirty.

1977 Ford F-100
400m/c6
280,000 miles
Stock on the outside
modified/rebuilt everything

 

Some EVAP systems do use a variable purge that utilizes a tube that outcrops into the air cleaner. The air passing across the end of the tube into the carb creates a slight vacuum that draws vapors from the canister to the engine. I've never seen one on a Ford truck. But your aftermarket cleaner may support this method of purging the vapors from the canister. Typically, I've seen two setups. One that utilizes a purge valve that sits on the canister that uses engine temp and ported vacuum to control the purge source. The purge tee's into the PCV with a vacuum restictor. The other system uses a solenoid that tee's into the carb bowl vent and is computer controlled. The later I've seen on '80s and up. I'm sorry I don't know how the older '74 purged. Essentially the idea is to store the gas vapors from the tank in the canister untill the eninge is running. Then the vapors are purged into the combustion chamber. How the purge works varies from make to model to year. Ask around, with time you'll get it going. I've been smogging my truck from the ground up and there's been a lot to learn. I have the EVAP working correctly, and yes my truck DOESN'T reak of gasoline -
'79 F100 300-6 A/T

 

The hose to the carb vents fumes from the bowl when the engine is not running. When you start the engine, a solenoid valve in the line closes to prevent it from sucking fumes from the cannister. The can is filled with a catalyst that turns hydrocarbons into co2. It vents it through a round mushroom-shaped vent on the top. I would just plug it off unless you're a tree-hugger.

 

EVAP 101:

1) Canister is filled with activated carbon granules that abosrb hydrocarbon vapors - just like a respirator cartridge.
2) Granules do not support any chemical reaction leading to decompostion of hydrocarbons - it's not a catalyic converter filled with Pt and other "addition" type metals.
3) The granules need to be replentished with fresh air (engine on) in order to continue absorbing hydrocarbon vapors (engine off).
4) Mushroom cap on the canister is to allow fresh air INTO the canister.
Carbs with a bowl vent have a valve (sometimes solenoid) that closes when engine is on not allowing bowl to vent. A Thermal Vent Valve (TVV - green/white) is located downstream that only opens when hood temp is hot (so, carb bowl only vents when engine is off and under hood temp is hot).
If you have a two hose connection to your canister - one comes from the tank - the other comes from the engine. There should be a purge valve (The purge valve is electronically controlled on younger trucks) that opens (at operating temp) to allow a constant / metered purge of air through the canister into the intake. This purge valve is connected inline with the carb bowl vent if applicable. That's the part you'll need to figure out. My purge is controlled by a ported vacuum off the carb that controls the EGR and purge signal to the purge valve located on the canister. A "T" off the PCV (purge source) draws the purge into the intake when the purge signal is evacuated. A restrictor is located in line with the PCV "T" line to allow a metered and steady flow of air through the canister into the intake. The purge signal is further more controlled by a Thermal Vacuum Switch (TVS) that fits into the coolant elbow. So, when the engine is warm and above idle, the purge signal line pulls a weak vacuum on the purge valve. The purge valve in turn opens allowing the purge source ("T" into the PCV) to draw air from the canister. Fresh air is introduced through the mushroom cap into the canister refreshing the carbon granules and dumping the hydrocarbon vapors into the intake.
If you don't purge the canister it will become saturated with gas vapors and your truck will always stink like the guzzler it is. From my understanding, prolonged saturation can lead to a ruined canister.
The EVAP system does not hinder engine performance as does the EGR. It's simply a matter of getting the parts and the plumbimg right. For those of us that have to deal with SMOG exams, EVAP is a must. I hope I have clarified this once and for all. If I was a tree hugger I'd been in a Honda forum.

 

Good lord! what a complicated explanation for a simple system! The charcoal canister absorbs the gas vapors. The tube from the canister to the air cleaner sucks them out when the engine is running! That's all there is on a 74! But even that information isn't necessary. Just make sure you have the tank vent line hooked up to the canister at the only place it will hook up, and run a flex line (proper size), from the other side of the canister, to the air cleaner hook up! Done!!! Forget everything else that has been said!

As for the posts that don't think there is vacume in the air cleaner assembly! Where do you think the engine gets its air from? It dosn't just FALL into the engine, the engine SUCKS it in! Think about it!

 

Most emmision systems are NOT simple. That's what I've never figured out about the government and the epa people. If they wanted people and their autos to conform to certain standards, you would think they would educate people more about the emmission systems and there proper operation. I also see people trying to pass strict emmisions tests on this board who are begging for information on how to do it right, with no resources whatsoever. It makes me wonder why the dude who "tests" and demands certain criteria wouldn't give out any info? I asked a mechanic friend who did visual underhood inspections if he really knew what he was looking at, and he said no. As long as the major components were there and looked like they were hooked up, there was nothing else he was worried about. And lastly, I disagree with vacuum being present in the air cleaner. There might be a slight vacuum at full throttle from a stock air filter, but that's why we run those fancy chrome hp air cleaners right? I also wonder if the open element air cleaners contribute to the gas smell under the hood anyway?

 

I bought this truck this way. It's pretty butchered up under the hood. I'm not very fimiliar with Ford trucks. After reading all the replys, I think I'll try just venting to the air cleaner. The only stuff I have to work with are the cannister, the line from the tank is still connected to it, and about one inch length of hose that aparently goes to the motor somewhere. Looks like they just grabbed a handful of emission hoses and ripped it off. Wish me luck.
Mark

 

To Franklin2

To disagree with the presence of vacume in the air cleaner assembly when the engine is running is wrong. That isn't a matter of opinion, it's physics! try putting your hand over the top of the carburator with the engine running! Sure feels like vacume dosn't it? Now with the air cleaner in place, and the engine running, try putting your hand over the snorkel opening. presto! vacume.

 

Re vacuum in the air cleaner. Don't confuse flow with vacuum. When you put your hand over the carb your choke it off and create vacuum. If you had a place to hook a vacuum gauge to the air cleaner you would show little if any vacuum unless you tried to choke off the intake. Think of it this way. The air cleaner isn't much of a restriction.If you didn't run an air cleaner would you have vacuum over the carb?
It does get complicated don't it/


1977 Ford F-100
400m/c6
280,000 miles
Stock on the outside
modified/rebuilt everything