[Mgs] "High rev'ing" MGA carb

[Robert J. Guinness]

After rebuilding the cylinder head and carbs on my 1961 MGA (with 1800 
MGB 3 main engine and original MGA carbs), the engine fired right up . . 
.  to 3000 RPM!  It appears that the rear carb is causing the high 
revs.  If I block about 80% of the rear carb's air inlet, it calms down 
to around 1500 .  The front carb is behaving appropriately.  I assume I 
have issues with the jet because the adjusting nut will not tighten.  
Here are my questions for the group's wisdom.  What is/are the likely 
cause(s)?  Can I fix the carb without removing it (man is space tight 
around there  --  but I hate dealing with the carb stud nuts, vacuum 
tube, spring holder, etc.)?  Can I just remove the rear carb?  Any 
helpful techniques or procedures to deal with these issues?  Please note 
that when I use the word "can", I really mean "should I do it as part of 
"best practices".

Thanks.
-- 
Robert Guinness
1961 MGA