MG Car Repair: Spark yellow, activated charcoal, rich mixture

Question
QUESTION: Hi Howard;

Thanks for your previous answers.

My 1977 MGB idle ok, rev up ok when park.  But when I shift to first and second gear, it wants to stall the engine.  The spark plug is black.  The test for spark on the spark plug is yellow spark (not thick blue).  I took the ignition coil to Autozone for testing and it was ok.
What else do I need to test and get my spark to thick blue?  What tools do I need?  Please help.  Thanks, Yung

ANSWER: Yung, if the engine revs ok and idles ok and the plugs are black, you need to address the fuel problem first, if the black is flat black not glossy black then it is an indication of an over rich mixture. If it is glossy black, that is an indication of oil burning and would be also noted for blowing blue smoke out the exhaust.
For a correct diagnosis of the ignition system you need to locate a shop that has a scope and have them put it on the scope to tell if you have any ignition problem at all in that area.
Howard

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

QUESTION: Hi Howard;

I got my problem fixed by removing a gas line in a trunk.

What happened was I connected a gas line from the gas tank to line to charcoal cannister.  Then I started having problem three days later ever since.  The car slowly came back to normal after I disconnected the gas line.

I think the previous owner disconnected this line for a reason - Charcoal cannister was plugged up.  My next thing is to clean the cannister out.

Thanks all for your help,
Yung

Answer
Thanks for the feed back, The information is useful to readers that may experience the same problem.
Even though we were able to open some canisters, we never found a source for the activated charcoal. We were told that once the charcoal was saturated with fuel, it was no good.
In your case something has completely clogged it up to a point as to prevent the venting of the fuel tank.
Thanks,
Howard