MG Car Repair: Ignition coil problem?, fuel air mixture, center bolt

Question
QUESTION: I am working on a 1977 MGB.  I have had problem with the starter.  Then I found I have a bad battery connection.  So the starter problem is fixed now.  I have been driving this car with bad positive connection.  The car drives good.
Now that I just tight the loose connection, I got different problem.  The car seems to drive very rich.  In the first and second gears it jokes when I hit the gas pedal.  The third and fourth gear is better.  I removed the spark plug, it is black. Was my ignition coil go bad as I troubleshoot my starter? I tried to adjust the fuel/air mixture in the carburator, but it does not help.  Do you think my ignition coil is bad? Please help.

Thanks,
Yung

ANSWER: Hi Yung,
I believe you need to check the auto choke as they are a common failed item.
Howard

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QUESTION: Hi Howard,
Thanks for your reply.

Can you explain how to check for the auto choke?

One thing that I did just before I got myself into this problem was connecting a fuel line (in the trunk) from a fuel tank to a fuel line that goes to the front cannister.  My separate fuel tank was missing.  Not sure by connecting the fuel lines would cause this problem?

I just drove the car again, and it jerked up and down very hard in all gears. But when I park and hit the gas pedal, the engine sounds ok.  Do you think I might have a clutch problem?  How can I tell if my clutch is bad?

Appreciate your help,
Yung

ANSWER: I would have to write a book on all your questions so I can only cover one at a time.

First warm the engine up and to test if the choke is on all of the time remove the three screws holding the retaining ring on the coolant section of the choke and pull the coolant section away from the choke assembly. Do not remove the center bolt. After you pull the unit away you will see a lever sticking out of the side of the choke assembly in a slot.

You can move the lever in the slot back and forth which is turning the choke on and off. Start the engine and manually move the lever and note that it chokes and unchokes the engine. Look at the spring with the squared loop on the end and note that it is what moves the lever so the lever must move freely. Note which direction you move the lever to make the choke go off and when you engage the loop on the end of the spring turn the coolant unit in the same direction so as to load the spring against the lever to make the choke go off.

Then install the three screws and retainer ring and see if you loaded the spring enough to take the choke off. If not rotate the coolant assembly until the choke is off.

Howard

---------- FOLLOW-UP ----------

QUESTION: Hi Howard;

I just tested the choke and it workd as supposed to.  The lever moved to the off position as the engine get hot.

I also test the ignition coil by starting the engine with a sparkplug on the engine block.  The spark is yellow color, not blue.  Can I tell the ignition coil is bad? Now I am on the next test.  Do you think the ignition coil or the clutch?  Which one is better for my next test.  Please let me know what you think.  

I appreciate your help,
Yung

Answer
Hi Yung,
Your test of Yellow spark is an indication of a weak spark (unless it was looked at in bright sunlight) A yellow or orange spark is a "red flag" to a mechanic and means a weak spark. So it needs to be tested on what ever ignition test equipment you can access. (a scope is the best) You should see a thick blue spark.
Howard