Julien, as others will surely tell you, add some user information in your profile so we know where you are located.  Sometimes help is available locally.

The timing right at TDC with the engine running at 600 RPM does not sound right.  Static timing just to get the engine started is more typically around 5 to 8 BTDC.  You may find you need to advance the timing from there once the engine is warm.

You commented about the firing order.  Remember that the distributor rotor turns COUNTERCLOCKWISE so the firing order is 1-3-4-2 counterclockwise around the cap.  Cylinder #1 is at the water pump end of the engine.

When you talk about adjusting the carb, the jet is not arbitrarily 2.5 turns down from anywhere, it is down from the point where the jet is flush with the bridge (flat surface) in the carb throat.

Also, since you have been working on the carb, check the float valve operation and setting.

Hello guys,

I have 1962 morris minor completely stock (engine, body, etc). I just purchased the car and I noticed a slight hesitation when the car was cold. 
I checked distributor cap, spark plugs, contact point, etc.
I noticed the plugs installed was for lawn tractor (short plugs), distributor was corroded and point toasted.
I decided to do a full tune up on the car : 
spark plugs (right one for the engine)
condenser
contact point
distributor rotor and cap
spark plugs wire
I also checked the valves clearance and the carb richness nut and this one was wide open (too rich). Usually the basic set up is about 2,5 full turn when the nut is fully closed.

The valve clearance was set at 0,3 mm.
The spark plug gap at 0,7mm
The contact point gap at 0,4 mm
Timing advance set at TDC at 600 rpm with timing light (vacuum hose disconnected), using TDC mark on flywheel.
When I restarted the car I have a lot of back fire from exhaust pipe and carb (looks like you swap 2 spark plugs wire), I rechecked the firing order and it's the right one.  
When I advanced the timing at 30° at 600 rpm it seems to run better but I still have misfire ???
I thought it was the carb, so I installed a brand new HS2 rebuild carb with EB needle and still does the same problem. When the richness is really too rich it's running a bit better but spark plugs getting black really fast.

One last thing, when I rechecked my contact point, there are burn spots on the point like the old one but the condenser is new.

I'm really lost and I don't know where I have to look now.

Thanks guys for your help.


Julien