'70 C10 Converting Vapor Can to Standalone Purge Valve

[Gromit]

I have the first year of the C10 with the Evaporative Emission Control ("EEC").

This was a California thing at the time; so the Vapor Canisters for the 1970 are no longer (readily) available.

The vapor cans for 1970 had an integrated purge valve and I read that the carburetor was jetted to take into account the orifice sizes and spring pressure of the purge valve diaphragm.

In later years they went to a different design of purge valve; sometimes electrically controlled, sometimes vacuum, sometimes integrated, sometimes not etc. But the short answer is that the Vapor Canisters that are available today are not generally backwards compatible to 1970.

Today I found a Napa Echlin emissions catalog and noticed that they do have standalone vapor canister purge valves.

So I am thinking of just installing a late type vapor can (that does not have the integrated purge) and then adding a standalone purge in between the canister and the various PCV, Ported vacuum and fuel tank hose connections.

So before I try and reinvent the wheel here has anyone with a 1970 California EEC truck already gone down this path who is willing to advise which Echlin parts to use?

I'll attach the Echlin catalog pages of purge valves and then of canisters (or at least the canisters where the catalog mentions Chevy Trucks)

[Gromit]

Here is the last page showing Chevy Truck vapor canisters from the Echlin Emissions Parts catalog (that wouldn't fit in attachments to my first post)

[72c105speed]

Found this one? The price though!!! Looks similar to a 91 s10 canister

http://www.ebay.com/ulk/itm/281922447671

[Gromit]

Thank you for that link to the NOS can - yep, $155 and that is just the bids so far - I'd guess it will eventually go for well over $200 - it looks pristine and I'd be bidding against the Pebble Beach Corvette folks..(not that there is anything wrong with them :-)

I'm holding out to try and convert to a EEC setup where the parts are currently readily available.

I still have to sort out how many inches of mercury it takes to hold open the purge valve verses how much I have at ported vacuum but I think it will be doable once I separate the components.

The one you found does look exactly like the one in my truck so that is very interesting.

I didn't know the vapor can was made or designed by Rochester

[tdangle]

Would it be possible th eliminate it completely? I have a 70 C20 350 and it doesn't have any of the emission stuff. And yes it's a California truck

[72c105speed]

Originally Posted by tdangle

Would it be possible th eliminate it completely? I have a 70 C20 350 and it doesn't have any of the emission stuff. And yes it's a California truck

I'm not gonna nag to put mine back in... I'm going to cap the tank or if I find a deal on a non eec tank I'll switch it out!

[tdangle]

Not sure what you mean by "I'm not gonna nag to put mine back in." I was just sharing that mine never came with any emissions systems as it has a higher gvwr rating. I'm sure it didn't come with any because my dad bought the truck new.

[Acorn]

Don't know if this will help...http://www.ifsja.org/forums/vb/showthread.php?t=174213

[Gromit]

Thanks fellas and I did see that canister rebuild thread from the Jeep forum; it is helpful.

The inside diameters of the three factory vapor tank connectors on my 1970 C10 V8 350 are as follows:

In from Fuel Tank Vent line: 7/32 inside diameter, 5/16 outside diameter.

Out from Vapor Tank to PCV lines: 5/32 inside diameter, 1/4 outside diameter.

In from ported vacuum signal: 7/64 inside diameter, 3/16 outside diameter.

I noticed that inside the purge valve on my 1970 when you pop off the cap on the vapor tank and lift out the rubber purge valve membrane - that purge signal vacuum line (connected to ported vacuum) goes from a 7/64 id at the opening of the outer connector connector down to less than the size of a small sewing needle under the purge valve membrane. So anyway that was interesting and surprising for me anyway.

In other words a normal wire paper clip is about four times too big for that purge signal line opening under the purge valve rubber membrane, even though the rubber line and opening itself is 7/64 ID

But for example in the photos from the Jeep forum the same area of their purge valve is about a 3/16 or so i.d. opening all the way through to the membrane area - so possibly that is why we see so many different purge valves and vapor tanks on offer in that catalog from Echlin - they look the same on the outside but the vacuum purge balance based on those vacuum internal diameter openings is different depending upon the year of the motor and the fuel set up.

Today I went to Petsmart (or was it Petco?) and bought a 40 ounce tub of activated carbon to refill my existing canister. From what I have read the vibration of the motor and vehicle causes the carbon particles to grind together over the years and make progressively finer dust in your vapor canister. Also all those years (okay only five or six) of leaded gas I'm pretty sure the contents of mine is HazMat with fours all around so it will be nice to get rid of that and change it out even if it is not exactly the correct type.