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Old Opeler
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Controlled Venting

1972 FSM "Evaporation Control System"

a) the fuel tank has a non-vented filler cap.

b) vent lines are joined in the area of the tank [one is connected to the filler tube below the cap and the other(s) to the top corner(s) of the tank itself.]

c) A plastic evapouration line leads from there along under the vehicle to the activated carbon canister.

d) there is a second line conected from the carbon canister to the vent on the carbutettor bowl.

e) fresh air enters the carbon canister through a foam filter at the lower part of the carbon canister and flows, together with collected fuel vapour to the port in the carb base.

f) Metered bores in the hose fittings of the fuel tank control the air - and fuel vapour flow through to the activated carbon canister to the carburettor, and the pressure release in the fuel tank.

g) the fuel tank is vented through the carbon canister and has no other connection to the outside to ensure fuel vapour does not escape to atmosphere.


.. or that is how I read it!
 

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nobody said:
I'm sorry but the tank is vented to atmosphere. I just looked at all the FSM diagrams and it seems a few lines aren't there. Then again 71 and 72 shows no fuel fill and 73 seem to avoid it completely, and for 69 and 70 it was a very grey area. I can take some pics or send you a few variations of how it was done over the years if that would help. A fuel supply system cannot be completely contained or even worse tied to strictly a vacuum source like the intake and not vapor lock... then again they had to do something with the unused fuel a solex couldn't deal with.
For a long time, two systems in my GT baffled me; the PCV (Positive Crankcase Ventilation) system, and the Evaporation Control System (the charcoal cannister). I was determined to figure them out, and they may be the two systems I am the most knowledgeable about.

The Opel CIH PVC system is unique, in that it doesn't have a PCV valve as in most makes (it uses a metered port), and the FSM is virtually silent in its function (except, I found later, in the "Tune Up" section), but Otto Bartsch was able to enlighten me. But that is covered in detail elsewhere.

The cannister system is pretty straightforward, but many GT's have been modified over the years (ditto with the PCV system), so it can be difficult to see how it USED to function. But the FSM was quite clear on its design and function, and I have posted two pages from the 1972 FSM, and one from the 1970 FSM. I have also posted an old Blitz article by Charles Goin. All the GT's used the same cannister system, but the '70 FSM had another photo. There is another photo I have seen that better illustrates the hose connections from the tank to the cannister and then on to the carb, but it isn't falling to hand this morning.

Anyway, to clear up a couple of points, from the factory, the GT tank is ONLY vented (via the cannister) into the Solex throat UPSTREAM of the venturi, and therefore sees only a small vacuum related to the pressure drop of the filter, NOT the full manifold vacuum. The gas cap is sealed, and if you don't vent the tank into the carb, then it MUST be vented to atmosphere. It works, and if you vent it such that it doesn't create fumes in the interior, it will work fine.

If the Solex couldn't handle all the fuel, it simply floods the intake. The exception is the '73 model, which has a special gas filter which uses a separate vapour vent port on the outlet and a return line to the tank. But the Evaporation Control System is otherwise identical for all years of the GT.
 

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Alot of info there but I didn't see anything on the 2 variations of fuel filler tubes or the changes in venting it caused. Not to mention the 2 tank variations. Books are great I have a good Opel library, I was on about the 5th GT before I knew a FSM even existed so most of what I do and know is just from having done it so many times. I told Dean what I know works. I started doing twin 1.9 motors in the late 70s and and do feel it's a subject I can speak of with pretty good authority.
 

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just a note on this subject

I recently replaced the gas tank and the vent lines were different from one to the other I also have several fuel filler tubes for GTs that are different as to venting. They were not all the same and venting was done different through the years. This is what I have found along with a few other deviations from factory stuff that I've seen so far. I'm trying to politely say that the books and prints are not always correct so some times it helps to listen to somebody that's been there not just look at a book and say that is it.

BTW I was under the impression this was about some of the finer points of twins not how to troubeshoot a solex.

I've run twins so long that venting was figured out some 25 years ago, the wagon had me stumped for a bit in 85 and the manta in 83 but I managed to get through it. To make a long story short I've run twins in GTs mantas and a wagon with alot of miles on them all. You can reinvent it or trust as you see fit.
 

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You're right Dave, this has gone way off-topic. What WAS on-topic was that it seemed that Dean had plugged the tank vent, which is a bad thing. Solex, Weber down-draft or side-draft. I was merely making sure that he didn't leave the tank un-vented.

As to the differences between what the FSM shows and what is really there, you are again right. The FSM's are often incorrect, as evidenced by the famous timing chain and crank key-way photo. On the other hand, the '73 FSM clearly shows the vapour return line from the special fuel filter to the tank, which may be the other type of tank you are referring to.

So I have agreed that you are right. Except when you say the GT tank is vented to the atmosphere. That may be the case in a particular GT that you have seen, or even several GT's, AFTER someone has modified the factory tank venting. But even the '69 FSM shows the tank vented to the carb via the cannister. Which it was from the factory.

And don't dismiss what I say just because I have read it in a book. I have also seen it first hand on at least five GT's, an Ascona, two Kadetts and a Manta that I have either owned or worked on.
 

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I agree I've seen it done a number of ways as well, both factory and after the fact. I was just trying to explain some of my experiences with it using twins. I made a run set up like I mentioned from Prince Rupert to LA then to El paso then back here with no problems. Pulling the hill out of El Paso is where I refigured the jetting for OEs. I didn't rejet it but still remember the numbers and correcting factors for sea level VS altitude. On twins I'm not bad but it took years to get there. I've never had a motor or even a design let go or have a problem..excluding the fire.

I like to share what I've learned over the years and since I like twins it's easy for me now. I started with a pair of OEs on a cannon set I got from Smitty before Bob was there at C&R.

Ok I've proved or at least tried to that I'm an old school Opel motorhead. In my gallery the gold car was the one that caught fire in 78 with twins and the white was the road warrior I built in 84 again with twins and 11:1s.

At some point it would be nice if I was understood to really have a clue of how twins worked in a GT. I figured the cold air cowl inducted OMs might give a clue.
 

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Pathologic Opeler
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Discussion Starter · #107 ·
redid my cable stop

its hard to find a place to anchor the cable stop. i have more secure cable stop now. i cut and bent some door hanger metal to shape. its held by 1 bolt on an unused throttle stop ear on the carb, its better than my first attempt.

it is stout. no welding was necessary.
 

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Pathologic Opeler
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Discussion Starter · #108 ·
Gabe Sanchez and Bruce Butler Were instrumental in the design, leverage modifications and expertise in my second overhaul and cable routing of the side drafts. I had prior pronlemsin my reassembly and contamination by ethanol gas, among other things. Not limited to just JB Weld, that’s an inside joke
Hats off to the Wichita Opel Club, the best Opel Club in the world, if not the universe
Gabe did a complete disassembly of my side drafts down to a bare body!
Every chamber every plug!

Gabe was also instrumental in doing small welding modifications, the gold metal piece was welded and extended.

My cable travel is smooth and solid. Gas pedal feels right. I did a 50 mile shakedown cruise last night.

I like the cable coming in front of the engine versus over the top via the mangolesti(sp?)

I also bought a big valve head from Gil, and the Shorty headers are sweet.
Gil fixed me up with the thermostat housing for the irmschers

The car runs really really well. It’s a miniature beast
 

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Awesome! Why did you change from your original head big valve head ?
 

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Looks very nice! Just thinking out loud, you might consider feeding those bad boys with a couple hundred CFM’s of cool air. It makes a big difference in stop & go feeding the cool air into the engine from in front of the radiator. Driving around in the 90° weather it’s made a noticeable difference for my downdraft. I’m convinced that the side draft intakes do run MUCH cooler than the stock downdraft🙂 Awesome set up Dean
 

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Opel Rallier since 1977
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Keep an eye on those filters if you ever have any backfires.They like to melt easily and also tend to start to disintegrate after a few years.
 
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