Engine runs erraticaly

[alex1019]

Hello, since I collected my 356 in Berlin it has been real fun. I drove to work everyday (approx 100km) and it works very well 1000km together since the car is here!
Since yesterday I find the car generally slower, doesn´t rev as good and accelerations are less linear...difficult to catch 130kmh now...Last week the car ran real strong, very smooth.

I must precise :

-the car has just been serviced with new carbs gaskets and filters.
-I just moved to Germany so I use a different type of fuel now
- I put additive when I fill up gas
- the car doesn´t loose oil. Fuel level OK
- Starts without any prob. (I only noticed that with hot engine, the idle was lower than last week (generator light even shows up)
- I ALWAYS respect warm up time
- I washed the car yesterday with high pressure underneath
- We lost 10 degrees in temperature compared to tuesday
- I haven´t checked the spark plugs yesterday but last week they were ok

So any idea ?
Carbs loosing settings after a week ?
Ignition ?
Moisture somewhere ?
Dirt in the gasoline ?

Thanks a lot for your help

[vwretrosteve]

check your points gap -

easiest thing to rule out -

[roy mawbey]

Alex,

Can't say exactly how many use additives in the fuel but I never have as the heads are aluminium and all have valve seat inserts which should not act in the same way with regression as cast iron blocks do using lead free petrol. I don't know which carbs you have are they Zeniths? The accelerator pump nozzles or the jets that supply fuel to the venturi's might have a blockage on one of them or the quantity of fuel delivered by them is incorrect. If you have no "backfire" from the carbs then has the timing slipped? Is the distributor clamp tight? If the engine has really just been worked on recently it might be something like that and you have put in by the sound of it some fast journeys. I would have thought? some miss-firing from the exhaust would be heard though?

Are the valve clearances okay still? Engines that have just been worked on are always a little suspect till the milage /kilometres have really built up a little.

Let us know, best of luck

Roy

[alex1019]

Thank you,

I looked again yesterday and :

Plugs OK
Wiring OK
No moisture in the distributor
Openned the gas tank to create a depression
I filled up the tank (cause I thought maybe I am running with the bottom of the tank and might be dirt in there...)
No back-fire
Slight miss-fire eventually but I am not an expert
Distributor clamp OK
Just a very slight leak at the bottom of the carbs (gaskets are 2 weeks old though!!) Bolts are all tightl
Carb linkage tight
Idle OK I think

Sounds like dirt in the carburetor or wrong timing to me...General loss of power with rattles and slightly more vibrations, feels like the tachometer is exagerating and showing alreday 3000rpm but speedometer says only 30 kmh! And before you ask me yes its not the handbrake

[roy mawbey]

Alex,

Sounds like you are actually running mostly on three cylinders or a blocked jet. I know you have checked the plugs but is there a good spark from them all? You mentioned before you had new leads are these modern type versions with a resistance of around 1080 ohms? Have you checked the resistance with a multi meter?

A faulty plug can give you all sorts of problems under load sometimes.
You could do a basic check of the timing as detailed in the drivers manual if you have one? If it was okay last week and the distributor clamp is tight and the point gap unchanged with no pitting its possibly okay.

If you have Zeniths a blocked idle jet can give you strange effects of power loss and misfire through the carbs. ( under the small square cover the idle jets are the top two on each carb. A bit of a devil to get to with the carbs installed but it is possible.)

If you are sure about the plugs etc, have a look at the idles they do more than just control the idle, it upsets the running if they are blocked. The main jets have a much larger bore never normally a problem.

Hope the valve clearances are okay.

Roy

[alex1019]

Thanks roy,

I went to the workshop the Porsche 356 club berlin recommended yesterday and the mechanic says the car is running on 3 cylinders in fact.
He has moved the condenser to the front of the distributor because he says he was too hot and has burnt the points (never heard about the importance of the position of the condenser ?) He said also one of the plug wires was too short and he replaced it.
He will check the valve clearance today, adjust the timing and the carburetors. He is going to take the compression of the engine but do you really think the car was running on 3 cylinders just because of the ignition issues or could it be something more serious like a burnt valve ? How much would mean such a repair ?
The car was running good last week and still starts really good. Idle is relatively stable as well. Haven´t noticed any sucking from the exhausts but.............
the fact that the car runs on 3 cylinders really scares me

[roy mawbey]

Alex,

If the condenser is not of the correct value (type) its very likely it will not control the spark value at the points and it will burn them and make them appear pitted. The position of the condenser though I have never seen moved to another position unless it was already incorrectly placed by someone else before you had the car.

The ignition lead length seems odd to question. Provided the lead was not pulled the the extreme to get it on the spark plug and the plug connector could easily be pushed on? can't see that would affect it. Of course if the resistance of the lead is incorrect or the plug has an internal fault.....

Did he actually remove each plug and see if the plug sparked?

Remember, on the 2 off Zenith carbs you have a total of 4 idle jets and 4 main jets as well as corresponding air correction jets. Each Zenith has 2 venturi's each with a pump jet nozzle you can see if you remove the air cleaner and look over the top of the carb. If you depress the throttle lever on the carb manually to the stop and look at the long nozzles you should see fuel coming out of each one. Has he checked that?

A faulty condenser or one that is burning points is not good but the spark is still going to 3 plugs at the moment maybe 4.

A faulty idle jet ( or main of course ) to one cylinder will take the engine down to three.

The compression test will show a result and some would say a leak down test would be probably even better. I have never had that done and I not experienced enough to explain the benifits maybe someone else can....

If it were a sticking valve I would have thought you would know from the engine noises??

Hope he finds the problem for you, keep us informed.

Best of luck

Roy

[alex1019]

Hello, I got the car back from the workshop and it runs real good again !
Thanks for the advices.

Basically :

New spark plug wire (one was too short and damaged)
condenser and points
Valve adjusment
+
King pin and link pin (the previous owner never heard about front axle greasing points it was dry like hell )
+
Almost no oil left in the gearbox (hasn´t been checked for long time )

PS (Roy, I also never heard before about the position of the condenser? well now its sitting in front of the distributor when you open the lid. I have never seen that on any other 356? will send you a pic, btw how do you recognize if the condenser if the good type ?)

[roy mawbey]

Alex,

Pleased its running okay now. I think you were possibly lucky that it happened as to run with a low gearbox oil level is not a good idea!

I don't know how he managed to fit the condenser to the front of the distributor as normally the connection wire hardly long enough to reach from the front to the contact breaker connection screw? I see no no logic in doing that, maybe others do??

The condensers seem to vary in specification to the distributor used. For the original Bosch distributor used on my 6Volt 1959 T2 "A" engine the value is: 0.27 -0.32 micro Farad.

It would be important I guess to state the engine you have to a known 356 parts supplier with the Bosch distributor info stated on the manufacturers identification plate.

There are a number of 356 parts people over here that will sell you the right items and advise on the phone: PRS services, Roger Bray, Karmann Connection to name a few. Trust these people, because in the case of condensers although they can arrive in a Bosch box they are not always marked with the value.

Get some spare parts catalog's from where you can ( Stoddard in USA do a good one also one on-line www.stoddard.com )With the layout drawings of many of the items it helps a lot!

Keep greasing and enjoy

Roy