my 66 911 has rough idle and runs rough (need help...)

[minimalcreative]

So, the ran has stopped in so. cal and the soft cover on the p-car has not kept the car as dry as it would like. I started and run it one a week during this wetest, or the wet seasons and now it is time to let her get some fresj air up the 2 freeway. But all is not good under the hood.

The engine had definite rough idle and once I took her out to get her warmed up, there were issues getting enough power to get up the hill outside the house. I was concerned.

But in the freeway the normal smooth acceleration has issues and is flat, pat, pat, pat backfires between 3 and 4,000 and well it does not improve...

A good and knowledgable p-car friend told me it could be blocked jets due to the sittng and rough conditins.

So I am looking if possibe for a side diagram of the webers so that I an try to take out the jets to carb clean and huff and puff them clean.

Any help out there? I have invested in new platinum plugs (the old NGKs where carboned upon review when replaced) and the spark was much improved.

Thanks. I have the flat blade screwdriver ready...

[304065]

What engine, 901/01 or 901/05? Weber 40IDA? What ignition, are you using the stock points or a bosch or aftermarket CDI?

Platinum plugs aren't that good, the standard NGK or Bosch are better.

[Grady Clay]

Have you done the requisite Search Function? Here is a thread:
“Weber Experts please”
weber experts please
I’m sure there are many others.



First some questions:

When you started it once a week, how did you run it – up
the freeway or sit and idle?

How recent are the cap, rotor, wires, and plug connectors?
Does it have a CD Ignition system?
Is the tach acting up?
Is there moisture inside the cap?
Are the distributor points clean and properly set?
What do the plugs look like right now?


Is the fuel filter clean?
Does the car have fresh gasoline?
If you use a long hose to return the fuel from the filter back
to the gas filler, is there adequate flow?

Now we can consider tinkering with the carburetors.

When working around gasoline, be exceedingly careful. Do
this outside and away from your house and other cars. Have
a BIG fire extinguisher handy but away from the car.

First you want to drain the float chambers. An easy way is to
loosen the main jet carriers and let the gas dribble out and into
a container. Use a 10 mm socket, not an open-end wrench.

Next you want to investigate the amount of sediment in the
float chamber. Use a Q-tip and explore in the threaded port
for the main jet carrier. This is a subjective observation and
the question is always how much is too much? If there is
“too much” then no amount of cleaning the idle circuit will solve
the reoccurring problem. This is the point where you need to
make the decision weather or not to remove the carburetors
for a through cleaning.

Assuming you decide to only clean the idle circuit you will need
some supplies and tools. You have the flat blade screw driver
in hand. Make sure the blade is a perfect fit for the idle jet carrier
and idle air bleed screw. You don’t want damaged parts from the
wrong size tool. You will want an air flow syncrometer, available
from our host. You will need aerosol cans of carb cleaner and a
source of compresses air. Have plenty of paper towels.

Here is a diagram of the idle circuit so we can talk about the
same thing. In actuality the idle air circuit (14), (16), and (17)
are on the same (outboard) side of the carb as the mixture
screw (20) and the idle fuel jet (23). The diagram shows it this
way for circuit clarity.
"
"
(C) Dr. Ing. h.c. F. Porsche A.G.

Porsche describes the idle circuit this way:
“The fuel is drawn from the emulsion well (12) through the
delivery port (22) to the idle metering je-t (23); it mixes here
with air which through the idle air bleed (24). The fuel/air
mixture passes through the delivery port (21) to the idle mixture
discharge port (19) which is located below the throttle valve
(18). The tapered idle mixture control screw (20) meters the
flow. Immediately above the throttle valve (18) are located two
transition ports (15) which begin to discharge additional fuel/air
mixture as soon as the throttle valve opens far enough to clear
these ports. This provides smooth transition from idling to
higher engine speeds.

“To provide equal flow of air through all three carburetor throats
when the throttle valve is set for idling, an air adjustment screw
(16) has been provided in each of the three carburetor throats.
These screws control the flow of air through the passage (14)
and, thus, the amount of air which is permitted to enter below
the throttle valve through the air port (17).”


From this point on – DON’T open the throttles. You can wire the
linkage if you want. If you drop something down the carb, it will
stop at the throttle valve. If you open the throttle valve it may
get past an intake valve and into the cylinder. A little care here
can prevent a disaster.

You are going to want to record the current placement of the
adjustment screws – idle mixture control screw (20) and the air
adjustment screw (16). You can do this by carefully turning them
in until they just touch the seat – no force! Count the number of
turns including fractional turn. Keep each adjuster associated
with its original location. Even though these adjustments will
change, this is a good starting point after cleaning.

Don’t change the idle stop on the end of the throttle shaft.

Remove the idle jet (23) carrier. It probably isn’t necessary to
remove the cover screw for the transition ports (15). That cover
screw is very difficult to remove and is best done with the carb
off the engine.

Remove the intake stacks and the air cleaner part. This allows
access to the idle air bleed (24). Be careful to not drop anything
in the engine. Many Webers have a little spacer under the nut
for the stacks.

You want to spray carb cleaner both directions in each passage
and blow out both directions with compressed air. Repeat
several (many) times.

Reassemble everything and get the adjustments back in their
original position. Take a flashlight and mirror and inspect the
throttle valve for anything that might have fallen in. Now you
can un-wire the throttles.

At this point you can turn on the fuel pump and refill the float
chambers. Do NOT turn the engine with the starter. Inspect
very carefully for fuel leaks. With the key OFF, turn the engine
with a wrench at least two revolutions. Make sure it is free to
rotate. What you are looking for is any chance that fuel or other
fluids have hydrauliced a cylinder and the off chance something
got in a cylinder.

Now you can start the engine. If it runs reasonably, take it for
a blast up the freeway.

I would have a couple of sets of new NGK BP7ES plugs handy.

Now you can get into balancing the air flow and adjusting the
mixture. The two adjustments chase each other somewhat.
That is to say you can’t set the air and then the mixture and
you’re done. You will also need to balance the carbs left-to-
right. A further refinement is to set the linkage where a slightest
movement at the gas pedal moves all the throttles off the stop
at the exact same time.

“While you are there,” clean and lube all the linkage from the
pedal to the carb.

After some highway miles (1-300) you might want to do some
final tweaks.

Enjoy.

Best,
Grady

[Grady Clay]

Here is the link to the Syncrometer from our host.

http://www.pelicanparts.com/catalog/shopcart/PORS/POR_PORS_PTOOLS_pg6.htm

Best,
Grady

[minimalcreative]

The car has newish cap and leads. The operation will begin this afternoon...
there is no CD Ignition system. too much on the go right now but a good upgrade I understand.
the tach seems accurate to the stuttering of the engine.
the points are clean and I will check the setting later.
the last set of plugs that came out (NGK) where pretty black.
cap is clean.
fuel filter clean appears clean.
fresh gasoline, yep, and expensive nowdays.
return the fuel hose. I will check on that...

thanks for the clean diagnosis...

[Grady Clay]

My point is that you may not need to go into the carburetor if there is some other issue. I suspect fowled plugs. Even if you just borrow a CDI for diagnostic and tuning purposes, it is worth it to keep you from going down the wrong path. I can’t imagine an early 911 without a CDI unless it is a show car that only has to demonstrate that it will start and run with all new components.

For a diagnostic tool for race cars and in the shop, I had complete ignition systems – distributor, CDI, wiring, transformer, cap, rotor ignition wires, and plug connectors – all known good. There are many situations where ignition problems appear to be fuel system related and vise versa.

On the other side of the coin, it is usual maintenance to periodically dissemble the carburetors for cleaning, replacing gaskets and other, and re-adjusting everything. If you feel the need to go into the carbs, take them off the engine and do them right.

If you have the carbs off, an important “while you are there” is to install two insulators between the head and intake manifold. This helps prevent heat soak vapor lock. The most difficult part is installing longer intake studs in the heads but easy with the right tool.

There are a lot of preliminaries to carb adjustment that are similar to the MFI Check and Measure part of CMA.

Best,
Grady

BTW, what is your name?

[JCF]

Great stuff.
Thanks Grady.

John

[minimalcreative]

Thanks for the update, I have just put in new plugs. I read a bunch of threads about which to try and ended up investing in the platinums. So I can expect that as the plugs only have 10/15 minutes running time on them that they are still OK.

great recommendtions supplied in this post. Is there a way to compile a trouble shooting the weber system posting? I bet it is one of the highest search fields...

Regarding CD ignition systems what is the recommendation? I am looking for something major around christmas and the rest of the family will be pleased to contribute to one item, I bet.


Neil

[304065]

Wow, I don't think I've ever encountered anyone still running the points ignition on a 2.0.

MSD 6AL and matching high-vibration coil is the ticket. Do a search here for installation instructions. Many swear by the Bosch CDI, as well, and if you're a stickler for originality, many cars were updated with this in 1969 when it came out.

The MSD will give you a fat spark, multiple sparks below 3000 rpm, and virtually eliminates wear from the points. You can open the plug gap way wide to eliminate fouling. It also has a built-in rev limiter so you can ditch those expensive mechanical rev limiting rotors and go with one from a beetle.