[Mgs] Fuel Issue

PaulHunt73 paulhunt73 at virginmedia.com
Tue Jan 29 01:36:49 MST 2013


On the face of it, if only one cylinder isn't firing it can't be the rear 
carb as that would affect a pair of cylinders.  But the MGB has a large bore 
balance tube joining all four cylinders so it's possible the 3rd cylinder is 
getting just enough mixture from the front carb but the end cylinder isn't. 
If it's only firing on three then you wouldn't really know if the 3rd 
cylinder were firing fully or not.

It's a simple check to tell whether it's fuel or ignition, after running for 
a few moments remove plug 4.  If it's wet or smells strongly of fuel then 
it's ignition.  If it's dry and no fuel smell then it's fuel.

A plug can fire when laying on the block but not when in the cylinder under 
compression pressure if the cap (or other HT component) is marginal and 
breaking down under the higher HT voltage that is required to fire a plug 
under compression.

After having the ignition on for a few moments it's another moments job to 
remove the lid of the float chamber to check you have fuel in there, i.e. it 
isn't a blocked float valve.  If that's OK remove the air cleaners and blow 
gently into the float chamber overflow port you *should* see fuel bubbling 
up the jet in the intake to check the jet pipe and jet aren't blocked.

PaulH.

----- Original Message ----- 
> ... After re-inspecting the plugs, it appears that the 4th
> cylinder was not firing, but the plug was not gas or oil fouled. 


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