MG Car Repair: 79 MGB will not start, pertronix ignitor, overflow pipe

Question
QUESTION: Hi.  All 4 cylinders have compression 130-135psi.  I have spark confirmed by timing gun and external view of spark on crank (from the plugs).  The twin HIF4 carbs have been professionally rebuilt ~1000 miles ago, I have fuel in cylinders (plugs get wet after cranking ad nauseam).  This car is a 'desmogged' 79 MGB that a previous owner put a modified cam into.  I had the distributor prof. rebuilt and it runs a lucas sport coil with a pertronix ignitor.  The car was running flawlessly up until the last month where it began to sputter and lose power at high rpms (3500)  eventually it started to do the same thing at lower rpms (~2200). Then it stopped wanting to idle unless the choke was on ... now it will only catch if the throttle is wide open and it labours to idle (very slow ) then dies quickly.  I'm at a loss.
Thank you!

ANSWER: Hi Lance.  If you have fuel in the carbs, and a spark, and air from the filters, then it should fire and run.  

1) Check the timing via spark plug #1 AND test again from spark plug #4.  Pertronix units are very reliable.  If they fail, they usually stop completely, they do not degrade.

2) It is possible that one carb has developed a fault resulting in an excessively rich mixture.  Pull all 4 plugs and inspect them.  Are one pair much wetter than the other?  There is a known weakness with the HIF carb that the choke mechanism has a rubber 'O' ring seal.  If this fails, fuel floods the carb and it does not come out of the overflow pipe.  

3) Spluttering at high revs can be using the wrong spark plugs.  Fit another set.  I use Bosch W7DC.  

4) Another possible problem is a failing fuel pump or a blocked fuel filter.  The AUF300 fuel pump does have plastic valves inside, and they often develop a split, which reduces the flow rate.  Do a flow test with a jam jar.  It should half fill the jar in less than 1 minute.  


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

QUESTION: Thanks Barrie, could you clarify point #1 in your response, please?  I'm assuming that you mean cylinder #1 but I'm not clear on what cylinder #4 should be checked for?
Thanks,
Lance

Answer
Hi Lance.  I was suggesting that you check the timing by attaching the timing gun to cylinder #1, and then do it again using cylinder #4.  They should give identical results.  If they do not, then I would suspect a fault with the Pertronix unit.  If you also do it with cylinders #2 and #3, but the timing mark will be 180 degrees out, so it is necessary to put a blob of white paint on the pulley to check these as well.