The fuel tank change occurred in April/May 1974. The carbon canister moved off the top of the fuel tank prior to this change. Was it at the end of calendar year 1973 or at the model change in the summer of 1973?

Here is info:

http://www.914world.com/bbs2/index.php?showtopic=346667

Hi Jeff -- so there are November 1973 cars with them up front. Is that right? 1/74 cars don't. So this is a calendar year emission change, yes?

Here is a 10/73 car with the front mounted canister.

I don't think a calendar year change would have been issued. Model year yes. Perhaps a mid-model year change if it was linked to a change in legal requirements, where teh emissions reqs did not change at the calendar year. Both cars with front and engine bay mounted canisters would function the same. The change required a different mounting bracket for the engine bay (congesting the engine bay), eliminated the 2 big supply/return air plastic tubes on the driver side valence and replaced them with shorter rubber hoses in the engine bay.

No real benefit or reason as far as I can understand. So far.

pretty bloody obvious from where i am standing.
having renewed fuel system on a jan 74 build (last week of jan).

you don't have to run a dirty fat pipe from air cleaner to charcoal tank through length of car. instead just a tiny small diameter line from charchoal tank to fuel tank through central tunnel if you put the canister in the engine bay.

only thing i would say is why did they not think of it sooner.
california had them bamboozled? the whole emissions scenario was intense and happening fast? like it had everyone bamboozled in order to clean up their acts.
it was on the fly and they were making it happen. a bit like now with co-vid.

you pick an appropriate moment to swing over.
train your production line workers to do the flip.
send them home for xmas and brief them when they come in the door for the new year.

you have xmas and you have the summer break.

and you deal with california and all the problems they kept on bringing to the table at those two times, if you can.

but i think in this case - its not about a reg change, usa already dictated sealed fuel systems, its about $, a penny here a penny there.

ps.
what i meant to say is i have an early build 74 1.8. they move the canister to the engine bay over the 73/74 xmas break. nothing to do with model years? everything to do with factory shutdown.

Mine is a '74 with an 11/73 chassis build date (April 74 assembly completion date) - a few hundred VIN#s later than the one shown. My cannister is in the engine compartment.

@starbear , sounds like your car sat around or was delayed?

mine has jan 26 production build date and is vin sticker 01/74.
in and out the door quick.

expansion tank is still steel, cannister is in engine bay on back trunk firewall.

change to a plastic expansion tank would be a simple matter on production line as it is an almost identical component made of a different material. could happen any time stock of new component came in.

changing charcoal tank location is more a build, assembly sequencing matter, and though it looks simple, enough is involved to brief workers on how it is to be done and to make sure the first installations go smoothly/correctly.

can't help think original cannister tank up front might be a production rationalisation/packaging legacy of accommodating 914/6 production. cars sent from karmann factory complete as possible with tanks and plumbing? tanks, cannister etc are as far as i know identical on 4s and 6s. original design considerations meant the best place for both cars was up front and not in the 6 engine bay?

as an aside, fairly sure euro spec cars don't have closed loop evaporation system.

to do 74 cannister change they had to alter the grommet in the tunnel/front fire wall to have a third small hole to take the fine line to the tank and an extra hole and grommet into the rear passenger firewall to take the same small line through the central tunnel from the engine bay.

also its not hard to imagine the system works better with the cannister closer to the engine fan bleed pushing the fumes out of the cannister into the aircleaner for burning.
shorter distances.

given that they did not need to deliver body shells to porsche after 72, it is surprising they did not do this change sooner in 73 or at the 73/74 model changeover when production would have halted for vacation.

maybe they had to get certification/approval from usa/california EPA/DOT bureaucracy and it delayed things? a fuel evaporation control system might have been a touchy area of regulation in the 1970s.

i realise looking at some other photos of engine bays that later in 75 it looks to be they mount the cannister off the side of the battery tray support.

shortens the fan bleed supply hose even more.

looks to me like they were ensuring the system actually worked.

must have been a significant velocity drop in the air moving through the hoses over length of hoses. esp in original location at front of car.

makes you think the original system might not have driven enough air through it to get the charcoal to release enough stored hydrocarbon to last the required 5 years or 50,000 miles.

don't know what the emissions warranty was for pre 74 usa models.
i still have the emissions warranty for mine with handbook.
emissions warranty was way longer than the rest of car warranty.
5 years or 50,000 miles.
at 50,000 miles the warranty directs to replace the charcoal filter.
so they had to work for/last that long.

maybe they were not making 50,000 miles still working effectively in the earlier locations?

i shall have to take a close look at mine to see where the small line from the fuel tank hooks up. even on the trunk firewall location its not exactly rational. the line from the aircleaner loops around and comes in from the right hand side. and the fan bleed line loops across and comes in from the drivers (left hand) side. you would think they would mount it so it took the shortest route possible? all the hoses are correct. now renewed but exactly copying and replacing original lines which were all correct and even still coloured (but only just, very faded, colour could be seen on underside of some lines).

never really thought about the charcoal cannister much before.
but i have been reminded how big a deal emission standards were.
the usa was doing it way in front of any other market.
it was new territory.

i know the second market to take all this up was australia.
basically it followed usa standards lagging about 10 years behind.
we took up unleaded fuel in the mid 80s followed by cats.
all the evaporation control gear was installed on cars here in the early 80s/late 70s.

europe lagged even further behind on those fronts.

another thought.
since this stuff is very fresh in my mind having just re-plumbed the car.

until jan this year it was a bone stock, unmolested preserved car. 1.8. L jetronic.

the plumbing shown in the factory manual absolutely accords with what was in the car.
the fan bleed feed supplies from the opposite side to the fuel tank vent line and air cleaner hose line.

this conflicts with what i looked up in the haynes manual. the haynes manual has a diagram that suggests it is the other way around.

i ignored the haynes manual and went with the car and the factory manual.
i knew the hoses were original on the car and trusted that.

i don't know if L jets are plumbed opposite to D jets. never really studied a D jet.

but it strikes me the original configuration of the cannister up front could mean there is a possibility of plumbing it up wrong, just depends i guess on how that hose from air cleaner and from fan join to hoses running length of car in/under engine bay. don't know as i have never studied any earlier cars to that level of detail? not really familiar with a D jet.

perhaps another good reason they put the cannister in the engine bay was in order for mechanics servicing car to know they were getting the plumbing right if they had disconnected it entirely for some reason. especially with L jets. i don't think you would want to mess that up with an L jet.

Yeah, probably delayed a while, maybe because it has the appearance group and needed a new supply of the special parts. For whatever reason, mine has many 73 parts (seats, gas tank, center bumper panels black not chrome, etc.)

@ starbear.

your car is a 2.0?

they must have had provision in the body shells for the changeover to engine bay cannister before the new calendar year commenced. admittedly fairly minor changes to the shell.

they seem to be doing two things in 74. first changing to a plastic evap cannister (i might be wrong) and then changing its position (3 times?).

wonder if the plastic cannister worked up front properly on L jet 1.8 cars.
its the first time airflow meter system is used on a car.
engine fan did pressurize (not much admittedly) the evap cannister that leads into the air cleaner up stream of the meter flap. must influence the system? maybe only minor?
they moved that cannister around 3 times in a very short period of time.

i have some stuff i collected back in jan when i got thrown off by the material in the factory workshop manual when i was putting new vacuum lines / fuel lines into engine bay.

at the time i was fairly convinced i had original lines in the car in original layout.
which turned out to be the case.
but i wanted to double check just in case - on the chance that someone during first owners time (first 15 years) with the car might have altered the layout.

first up.
the "diagram layout" that appears in the manual.
this shows the fan bleed is connected next to the small diam vapor line.
the air cleaner line is on the opposite side of the filter.

i believe this is the first configuration that is installed in the cars.
it is also the same as was installed in 911s up to some point in the early 70s.
not sure on cut off date.

Click to view attachment

here is the page from the manual showing the layout.
agrees with diagrammatic layout.
air bleed from fan attaches next to small diam vapor line.
line to aircleaner on opposite side.
Click to view attachment

here is another page from the same section of the manual (group 2 fuel injection).
some of you knowledgable types may have spotted this before.
looks very similar except the configuration of the cannister is reversed.
its a detail you might gloss over unless you were like me noticing that some of these diagrams did not accord with what was on my car.

my car, 74 1.8 agrees with this diagram.
(not the two diagrams above).

Click to view attachment

regarding above.

at first i thought there had to be errors in the manual.
contradictory information.

i did some research on 911 systems while i was trying to satisfy myself.
during the 70s 911s seemed to go through a similar evolution.
its virtually the same system, fan driven air is used to ventilate the cannister.
vw beetles used it as well, and i guess the rest of the air cooled vw models.
(i don't think water cooled cars used anything like this with a fan bleed pressure hose).

version 1 of the 911 was an air bleed line from fan into cannister with vapor line beside and line to aircleaner at opposite end.

version 2 was an air bleed line from fan into cannister and at opposite end vapor line in and line to aircleaner out.

version 3 deleted the air bleed line from the fan. system was truly closed.

1974 1.8 L set up is same as version 2 of 911.

made sense to me back in jan when i worked it out.
there is no valve (purge valve) in these early systems.
the part that is closing the system to the atmosphere are just charcoal filter particles.
(it is technically open to the atmosphere through the air bleed line from the fan),

in the earliest version they have the air bleed line directly next to vapor input line.
not sure what the cannister internals were like. but if they were in this arrangement then it would have meant a very short depth of charcoal particles for fumes to pass and escape via the air bleed line - especially during the phase when a car emits most vapor emissions, right after you have driven it for a while and then parked and switched the engine off.

the second version, as is definitely on the 74 1.8 means that any fuel vapors in that vapor line have to pass the full length of the charcoal cannister to escape out the fan air bleed line after a hot switch off. the full depth of the charcoal cannister contents is effectively the purge valve. the air bleed line to the fan is a weaker link for fumes to escape than the air cleaner intake line.

the fan link up via a bleed line peculiar i think to air cooled vws and porsches works to purge the cannister when your running the car. the longer and faster you run the car the more you purge the cannister. which might have been why they were progressively shortening the fan bleed hose throughout 1974? not sure.

there is a definitely a change in this cannister set up and hose layout design.
whether it occurs in 1974 or earlier i can't tell. but the 1974 1.8 L do not appear to share the hose set up into the cannister that much earlier cars used.