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Hi, I have a 1965 Mercedes W111 250se Coupe with 6 cylinder Fuel injection M129.1 engine.
Its in very good order and I’ve owned it for 14years now.
Unfortunately, in the past few years I didn’t use it much and the fuel went bad.
I cleaned out the tank and installed a new fuel filter, Cleaned the fuel pump out and flushed the fuel.
I use 100 Octane fuel with Valve shield and fuel Stabilizer.
It starts well and runs nice when cold idling at 900rpm but when it gets hot to normal running temperature it will Stutter/ hiccup and will stop. It is difficult to start again until it cools down. You can run it when its hot at about 3000rpm and it wont stop but this isn’t much use if you need to stop and start again.
Firstly, I thought it may be the thermometer in the Fuel injection pump not working to change Fuel/Air mix as it warms up. So, I installed a new one of these and the fuel mix valve is free and moves down as expected.
This didn’t help. I installed a new coil and this didn’t help.
I live in the lower island of New Zealand so the closest mechanic which would probably know anything about these cars is probably in Sydney Australia. I have a full-service manual but can’t find anything relevant.
Just wondering if anyone has any idea on what this could be.
Could it be the vacuum line to the points/timing issue?
Why 100 Octane?
Car like this does not need that high octane and is not helping it run better when warm since high octane means slower.
Have you made any timing adjustments due to higher octane fuel?
Was it using this fuel before it sat?
What did it do before you changed all he parts when you let it sit for a while?
So if it sat for a long period how long?
Is it possible vacuum lines dry rotted and leak now?
Some seal somewhere rotted and is not sealing?
Fuel injectors gummed up?
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