Brad Maynard

I removed tank from my 71 in hopes of finding build sheet, but instead found a black plastic box thing mounted on side which has two hoses running from it (which are currently connected only to bolts inserted at the end of each hose).

The black part is a Rochester part number 7028035. I have learned that this is apparently a Fuel System Vapor Separator from a quick search on Google and was apparently used on 70-74 cars. Anyone know what this thing is supposed to do and what the hoses should be connected to? My car does have a vapor cannister but I do not believe this could go directly to it as there is only one line which appears to run along frame on left side up to vapor cannister.

Also did only certain cars have this or should all 70-74 cars have this?

TonySinclair

My car ('74) has one. I believe one hose to the vapor cannister, and one hose to a vent on top of the tank...but don't quote me on that.

shafrs3

The fuel tanks were non vented, meaning not vented to the atmosphere. When the engine is not running, fuel tank vapors are passed through that separator to a 1/4" steel line that runs along the frame rail on the drivers side and collects in a charcoal canister located under the master cylinder. When the engine is started, engine vacuum opens a valve on this canister and allows the engine to draw the collected vapors from the canister into the intake system for combustion. That separator returns any liquid fuel entering the vapor recovery line and routes it back to the fuel tank. One hose goes to the tank and the other goes to the line heading for the charcoal canister.

cardo0

Just got my replacement liq sep from Zip and they ain't cheap ($60). Used with unvented systems to collect fuel vapor from tank rather than release to atmosphere like pre-'70 vented tank cars. U need to use an unvented cap also to make them work.
Busted mine when replacing tank and at the time no replacements availible. Well now there are brand-new replacements and lucky for me as my repair wasn't working and i managed to fill up my brand new NAPA EVC ($50) with fuel slosh. Topped off the tank and just made enoug of a turn to fill up the vapor line with slosh too. Not very funny to open the hood and see fuel bubble out next to exh hdr pipes - vettes always attract onlookers with the hood up. :o

So yes only 1 line to EVC (evaporative vapor canister) is right. I recall short 3/8" flex fuel line to tank and a longer flex hose to that rigid line. Blew out my vapor line with compressed air to verify it's open - well i know its open for sure know.
U may want to replace that 30yr old EVC also as charcoal inside will be 30 - well 35yrs - old now. NAPA prices have gone up to $90 and i bought my second replacement from ....... (oops, PM me for non-supporting vender info) for $50.

I recall not all '71 cars had non-vented sys but if u have an EVC then your car came with a non-vented sys.
And there's more to the sys as how it works with the carb but good enough for now and post if u need more info/help.

Hope this helps. cardo0

Brad Maynard

thanks guys this is very helpful.

I will need to replace this part now that I understand how it connects. I broke off one of the hose connectors.

Do you know which line (bottom or top) goes to tank and which to line to cannister?

cardo0

Yea, its a float type check vlv so the tank connects to the bottom while the vapor only end to the ECV is at the top. Got'a little ball for a float inside and when fuel/liquid enter bottom to float it the ball forces a needle type seat above it closed.

Liguid should drain back to tank on left turns and allow vapor to flow the ECV.

Good luck. cardo0