Early 911 vapor hose question

[C4 Pazzo]

I'm replacing the fuel and vapor hoses on my '70 911T and have a question. Is there supposed to be a hose connected to the left side of the T-fitting on the forward left side of the air filter (on the opposite side of the clamp marked as "19" on the image below)?



I don't recall there being a hose here, and if there is supposed to be one, I have no idea what it would connect to. If there isn't supposed to be a hose, is it supposed to be capped?

Thanks for your help.

[Jim727]

It looks like you have a diagram for an MFI air cleaner housing. The MFI units have a spray bar for fuel enrichment with the incoming fuel connected where you describe. The carb cars do not have or need the spray bar and it's not part of the vapor recovery system.

I think someone (Grady??) posted a good diagram of the early vapor recovery system in another thread.

Jim

[Grady Clay]

”tank ventilation-MFI diagrams“

I think we concluded from the above thread that the ’69 and RoW systems may be simpler and this was only for USA and a few other.

At the rear of the air filter assembly there are three hoses; the oil/water drain from the bottom that goes to the “dribbler” at the engine oil cooler, the crankcase breather from the oil tank and the return from the charcoal canister in the fuel evaporative emissions system.

Best,
Grady

[C4 Pazzo]

Thanks for the responses. Of course, my car is not an MFI. I wonder if the fitting is meant for a later type of emissions vapor recovery. The car had A/C retrofitted and the intake is oriented to the left instead of the right to make room (for the since removed) compressor. Perhaps the air filter box is from a newer car.

Looking at the ventilation diagrams reminded me of another vapor system question. When I cleaned out the vapor lines with compressed air, the line that I thought was coming from the fan into the charcoal filter spewed out foamy gunk that looked like the frothy oil/water mixture one sometimes sees. I was surprised to see it in that line, but now I wonder if I might have my inputs and outputs mixed up, since it seems more probable that oil might have gotten into the other line since it is connected opposite the oil breather hose.

I took a look at the two diagrams below from the thread Grady linked and noticed that for the early cars the line into the charcoal filter is connected at the side of the filter with two connections, whereas for the '74-'78 cars the input line is connected to the side of the filter with the single connection. I was relying on my Haynes manual and now wonder if the diagram shown was for a later car. It seems a little odd that the input and output connections would have changed unless the charcoal filter design changed (or maybe the direction of flow doesn't really matter), but I think I better go with Grady's early diagram as the guide and reconnect the hoses.

[Jim727]

The 18 and 19 fittings you indicated are definitely for MFI. It's possible you have an MFI air cleaner even with the carburetor car; a friend of mine received his that way right off the showroom floor. The enrichment solenoid (4) feeds fuel to the "T" connection on the driver-side of your air cleaner housing, continuing via your tube 18. The evap connectors are on the center of the air cleaner (suction line) and the fan shroud (pressure line).

[Image deleted]

[Grady Clay]

Here is the previous thread: ”MFI Problems“

The wrong one was published in Christophorus and the Factory Workshop Manual.
Later Workshop Manual up-dates had the correct version.
The correct version is in Bruce Anderson’s book, p. 84, 2nd Ed.
"
"
(C) 1969 Dr. Ing. h.c. F. Porsche A.G.
"
"
(C) 1969 Dr. Ing. h.c. F. Porsche A.G.


Best,
Grady

[Jim727]

Originally posted by Grady Clay
Jim,

That fuel plumbing diagram is wrong. Please deleat it and I'll post the correct version. Porsche made a serious mistake. They published this incorrect version in the Workshop manual and even in Christopherous.

Best,
Grady

Done.

Grady, your diagram still shows the fuel line running from the enrichment solenoid to the air cleaner "prime" tubes. Perhaps you can clarify the exact function of those tubes as opposed to the evap canister and associated plumbing.

Thanks for the correction!
Jim

[Grady Clay]

Jim,

I probably make one mistake per month. The beauty of this Forum is those errors get corrected. As you can see, even Porsche makes mistakes.

The cold start enrichment is straying from the evaporative emissions somewhat but the hoses shouldn’t be confused.

The upper (wrong) diagram above is for ’69 only (you can see the two solenoids on the MFI pump). The ’69-’71 MFI had the cold start enrichment in the air filter assembly. That causes regular fires. When the air filter assembly was steel (’69-’70) and the intake bells were steel, the fires weren’t any issue. Porsche changed the air filter assembly to plastic in ’71 and many (most?) intake bells were plastic. Those proved to be disastrous when a fire occurred. Starting in ’72 everything was plastic.

Note the lower (corrected) diagram is for the ’72-> system. The cold start enrichment was moved to the bottom of the intake stacks. The propensity for fires was reduced but not eliminated.

Most (good) advice recommends disconnecting the cold start enrichment or change it to button operated.


For the fuel evaporative emissions there are steel air filter assemblies both with and without the connection for the vapor hose. I think all plastic assemblies have the evaporative hose connection. For RoW, some had a plug in the port for the evap hose.

The question that taxes my memory is for MY ’69. Not all of the USA ’70-’71 (and later) system were in place. I’m sure there were mid-year additions leading up to the full ’70 system. None of that is well documented.

Best,
Grady

[Jim727]

Grady - what's the trick? I make about 30 mistakes a minute....

Very interested in the MFI since I just converted my 2.2T to a 2.2E ('71) and have lots to learn. Loving it! Will have it at the San Diego Parade.

The reason I keep focusing on the connections to the MFI enrichment is because C4 Pazzo's original post referenced both fuel and vapor hoses plus the hose connections associated with clamp "19"; those can't be evap hoses and I think they should be plugged for a carburetor car.

[BlueSideUp]

I have my airbox off of my '70 T right now and the two small fittings on the back of the airbox were just connected by vacuum line together.

My new owner's manual (just came in the mail!) shows a small hose attached to the intake pipe. I take it this is the carburetor heating mentioned in the manual, "carburetor heating will not be working with the heat lever in the down position". Did everyone ditch this hose early on? Should I cap off the other end where the hose attaches?

The drain line at the bottom of my airbox wasn't connected to anything, any idea where to find the oil cooler "dribbler" connection?

[C4 Pazzo]

I think you'll want to connect the carburetor pre-heater hose, though I don't know why it wouldn't work with the heat lever in the down position.

The oil cooler "dribbler" connection is the one labelled #10 in the diagram in my first post above. It's possible yours is still attached and all you need is about a foot length of 7 ID/12 OD vapor hose to connect to it from the bottom of the airbox.

If it isn't there you probably could buy one from our host.

[BlueSideUp]

The line attached to the bottom of my airbox was about 8 inches long and ended up dumping oily mess all over my engine shroud. I remember the hose being pretty small, way less than 7/12mm, more like the vacuum lines.

The picture in the manual shows the carburetor pre-heater hose running over behind the oil tank filler, below the oil filter, and toward the back of the engine compartment. I've never seen one connected in person.

[Jim727]

Carb preheat is a hose about 1" in diameter that runs from the heat exchanger to the air filter snout. If you look at C4 Pazzo's schematic, the air filter snout has a "Y" shape at the end with a larger opening for combustion air and a smaller tube extending downward near the combustion air opening - that smaller tube is where the carb preheat air enters. When the heat lever is down hot air from the heat exchanger is dumped overboard; with the heat lever up hot air is diverted into the cab and into the carb preheat tube. Carb preheat is only really needed where carburetor icing is an issue.

At the back of the round portion of the air cleaner there's a "T" fitting with a large and small connector. The larger has a brass flame-suppressor material in it and that connects via a tube to the oil tank to pull oil vapors in for burning. If that hose is not correctly connected you can get a real mess.

Here's the layout: On the round portion of the air cleaner there is a small tube at the bottom - this is the connection to the "dribbler" (No. 11 in the first schematic, connected to the air cleaner at the bottom by hose 12). At the back of the round part of the air cleaner, there is a "T" that connects to the oil tank via a tube (discussed above) and to the evap canister to pull in gas fumes. Now, if you have an MFI air cleaner, there is also a connection in the top of the air cleaner over each set of stacks that accepts enrichment fuel. These look to me like the bits that are connected by hose 18 in C4 Pazzo's schematic and then by another hose to the enrichment solenoid (4 in Grady's schematic). My 2.2T engine air cleaner did not have the fuel enrichment spray bars - I had to replace the air cleaner top with one that did have spray bars when I upgraded to a 2.2E MFI.

Much easier to point to the parts with a car nearby.

[C4 Pazzo]

Looks like the consensus is I have an MFI airbox on a non-MFI car; so I assume I can block off the extra opening in the "T" (though it apparently hasn't harmed anything being open for 37 years, so maybe just leave it alone).

Any thoughts on why the input and outputs for the vapor hose/charcoal cannister were swapped for the '74-'77s as compared to the early cars? Perhaps the direction of the flow makes no difference in a charcoal filter?

[BlueSideUp]

C4 Pazzo- I just looked at my airbox and I have the same arrangement as you. The spray bar T fitting on my car was also not connected to anything.

[C4 Pazzo]

BlueSideUp - thanks for checking.