68S Dizzy specs

[RMartin]

Had a local guy take a look at my Dizzy. He didn't know a thing about Porsches but here's what he found.
Crank RPM Crank Degrees
800 0
1000 6
1200 10
1800 16
2400 20
7000 24

Does the Dizzy move a total of 25 deg.? 5 deg. static timing plus 25 deg. from the Dizzy would be 30 deg. Right or wrong?

[RMartin]

The dizzy is a Bosch 002.

[Grady Clay]

RM,

Your distributor curve looks OK. Here is the spec sheet. Note
these are distributor RPM which are exactly half the crankshaft
RPM and distributor shaft advance which is exactly half the
crankshaft advance. The ignition timing spec for a 2000S engine
is 31 degrees at 6000 RPM. I would start slightly conservative
with 28-29 degrees at 6000 RPM. Be sure you have fresh high
octane fuel and everything is working properly.

Once you have the timing set at say 28 @ 6000, note the
advance at idle and static (engine not running). You can creep
up on 31 degrees. Too much advance will put a hole in a piston.

Make sure your distributor clamp won’t let the distributor move at
all when the clamp is tight. This is a common problem with early
clamps.
"
"
(C) 1967 Dr. Ing. h.c. F. Porsche K.-G.

Best,
Grady

[RMartin]

I have had trouble timing this car since I bought it. It WILL NOT run at 30 deg. advance. Pops and back fires starting at 5000k. The more I turn the dizzy the smoother it runs. Timing ends up about 36 deg. It doesn't ping and there are no signs of detonation on the plugs. I know this is not right but I've been trying to figure this out for 2 years now. Any ideas?

[6771911esses]

Is your cam timing ok????

[RMartin]

I don't know. Can it be checked with the engine in the car?

[6771911esses]

You may have to lower the engine in the car. Not a full removal.

MN

[ValveFloat]

Originally posted by RMartin
I don't know. Can it be checked with the engine in the car?

Yes it can. When I did it I removed the panel between the bumpers, the muffler, and the rear piece of sheetmetal.

Its interesting to me that those curves above are flat in the middle. I had the curve for my 68L dizzy checked, and it looks a lot like that, but it seemed wrong to me. Seems like every other advance curve I have seen is steeper in the beginning and then plateaus, without the rise at the end.

[Grady Clay]

Yes, you can measure the cam timing with the engine in the car.
You need to carefully adjust the valves (particularly #1 and #4
intakes). Always turn the engine clockwise. Since you don’t
have the chain covers off, you don’t want to “back up” the
engine and get any slack in the chain. That will give you false
cam timing readings.
Besides the valve adjustment tool, you will need the little
“Z-block” holder and a dial indicator.

All that said, let’s back up a minute and look at the problem. You
said it brakes up when you try to go over 5000 RPM. Will it free-
rev to 6000? When it brakes up is it load dependant (does it
brake up sooner or more the greater power you demand from
the engine)? Are there any other running issues or symptoms?

There are three possible areas to investigate. First is the
machinery. Once you have set the valve adjustment and
confirmed the cam timing is correct you need to look farther.
Have you inspected the sump screen? Look carefully around the
perimeter of the screen where it adjoins the crankcase. Look for
any foreign material. Post some clear digital images.

Measure the cranking compression and cylinder leakage. This will
confirm the cylinders, heads, and valves are sealing and pumping
properly.

Now let’s check the fuel system. Do this out of doors and away
from your house and other cars. Gasoline is very dangerous.
Safety first!

Take a long fuel hose and connect from the outlet of the fuel filter
(just prior to the Tee assembly to the carburetors) and run it
forward to the fuel filler at the RF fender. Confirm that it will flow
something greater than about 900 ml/min (30 fluid ounces per
minute). Note if the flow is greater at the start and reduces
after a few minutes of pumping.

With the fuel line reconnected, install a Tee and fuel pressure
gauge. The fuel pressure should reach about 3-4 psi after the
carburetor float chambers have filled (you will hear the pump
slow).

If above checks OK, on to the carburetors. Take a flashlight and
mirror and inspect the air correction jets (3 - green) in the top of
the carburetor. They are located between the intake stacks (red
arrows). There is one for each cylinder where two of them are
between #2 & #3 intakes and one between #1 & #2 intakes,
closer to #1. The orientation is similar for #4, #5, & #6. The left
in the diagram is to the rear of the car.
IMAGE WeberDiag01a.jpg “
“
© Dr. Ing. h.c. F. Porsche A.G.

The jet is brass, has a screwdriver slot and a center orifice.

What you are looking for here are small black/brown flakes that
can plug the air correction jet. You may find these flakes on the
top of the carburetor also. If so, they probably came from the
steel air filter assembly. It can get rusty where there is a double-
wall baffle at the crankcase breather connection.

If this checks our OK, drain the float chambers (4 total) using the
drain plug (red arrow below) with a 10 mm box wrench. Take a
Q-Tip and investigate the debris on the bottom of the chamber.
Be careful to not damage the brass float just inside. It is a
subjective call as to how much brown crud is too much. Post
some images.

Now remove the main-jet carriers (green arrows – 6 total).
Inspect for debris plugging the jet in the end of the carrier.
Clean if necessary. At this point you can spray some aerosol
carb cleaner down the vent in the top of each float chamber
(between the air correction jets) and let it drain out onto a clean
towel. You will get some indication of how much crud there is in
the bottom of the float chamber.
IMAGE WeberDiag02a.jpg “
“
© Dr. Ing. h.c. F. Porsche A.G.

Usually when there is a lot of crud in the float chamber it is the
idle jets that get plugged up first. This doesn’t sound like it is
your problem. They are easily accessible with a screw driver.
The idle jet carriers are at the blue arrows below.
IMAGE WeberDiag03a.jpg


If the carburetors are contaminated internally, they should be
disassembled for cleaning and new gaskets, etc. I am assuming
that these are the correct carbs for the engine and someone
prior hasn’t changed jets to something inappropriate.


OK, now to the ignition system.
I assume you have changed spark plugs several times. What
brand and type?
Are the plug connectors, wires, cap and rotor all in good (like
new) condition? Have you test changed coils? Is there a CDI
installed? Do you know that it works?

When the distributor shop ran your distributor, did they set it up
using a complete ignition system? Is there proper ground
between the points plate and the distributor housing?

A remote possibility is the plug wires are off by one cylinder when
installed in the cap. Put the engine at TDC #1 compression and
confirm the rotor points to #1 sparkplug. Rotate the rotor
(advance direction) and confirm it increases proximity to #1
terminal and not another.


All of these systems must be correct for the engine to run
properly. Please report back images and what you find.

Best,
Grady

BTW, where are you in Kansas? We travel I-70 regularly with
Chris in college in Fulton, MO.

[RMartin]

Right now I've got the carbs and intakes off doing some cleaning and painting. I had some issues with small particles from the tank getting in the carbs. While I've got it apart I'm going to seal the tank also. All of the ignition parts are brand new. Stock 68 so no CDI. I also have had a problem with the carbs in hot weather. I've been told it is fuel percolating in the fuel bowls so I am going to try to correct this also.
As far as the timing when I first bought the car the timing was set at about 36 deg. I've been trying to get it to run at 30 deg. When the carbs are clean it pulls strong to 7000k. The guy I bought it from told me that he and a buddy rebuilt it. Kinda makes me wonder if they new what they were doing. He gave me all of the old pistons and cylinders so I'm reasonably sure it's been rebuilt. No smoke or strange noises, just won't time right. I've been running NGK B8ES but bought B7ES to install.
I live in the very SE corner of KS. Little town called Riverton, about 15 miles west of Joplin MO.

[Grady Clay]

With the carbs off it is easy to inspect the air correction jets

While you have the fuel tank out, remove and clean the fuel screen fitting. That is commonly covered in fine rust particles.

It would be very beneficial to use a CDI. You can paint it flat black and hide it behind the 1-2-3 carburetor if you want.

In ’71 Porsche used a phenolic insulating spacer between the head and the intake manifold. This was on the 911T and did a good job of reducing fuel percolation in the carburetor. I use two insulators and three gaskets on each head. Any spacers require longer studs in the heads. You can use a proper fitting gasket to match the insulators to the intake port in the head and the intake runner in the manifold. The only other consideration is to check for clearance where the throttle linkage goes through the sheet metal near cylinder #3. These parts are available from our host.

Another possibility for your timing issue is the pulley could have been left loose and sheared off the index pin. It could have been reinstalled without a pin several degrees off.

Yes, BP8ES is the correct plug when running right. B7ES is good for testing just not sustained full throttle. A CDI will really help.


Riverton isn’t exactly on the I-70 corridor but perhaps we can connect some day. We are regularly in Pleasant Hill, MO; SE of KC.

Best,
Grady

[RMartin]

Thanks for the help Grady. Probably take me a couple of weeks to get everything back together, we'll see what happens.

[Early_S_Man]

Rmartin,

I second Grady's suggestion to get a Bosch CDI system installed on your engine ... less trouble than installing a new radio!

Here is a scanned copy of a magazine article regarding cam timing for a 911 engine:

http://members.rennlist.org/911pcars/camtiming-1.htm

Here is a scanned copy of the Weber service manual:

http://www.pbase.com/911r/weber_service_manual&page=all

[RMartin]

Thanks Warren.

[RMartin]

Where can I get a Bosch CDI unit. Does someone remanufacture them?
Last night while clean the intake manifolds I found a couple of hairlline cracks around the base. Getting them repaired.

[B D]

FYI