MG Car Repair: Baffled, fuel pressure gauge, vacuum gauge

Question
Hi Howard, you helped me a couple weeks ago with problems getting my '76 B, just stored for 10 years, through emissions.  I have since replaced the cat, resonator, and points.  I set the ignition timing and leaned the carb all the way out.  The car then ran OK in the garage, but it started running pretty hot.  I took it for a shakedown drive, and within a mile or so it started dying.  It would start kind of stalling, and sometimes it died entirely.  Took a bunch of revving and restarting to get home.  By that point it was way hot.  

The only idea I have is vapor lock.  The fuel pump has been moved to the engine compartment, and I'm in Denver.  I didn't have this problem before installing the cat, but the car wasn't running this hot before - maybe the overheating is a clue?

Thanks as always,
Billy

Answer
Hi Billy,
Installing a new CAT can not cause it to run bad. You can have a misfire on a cylinder first that can melt a CAT thus causing excessive back pressure. This can be tested by taking a short piece of brake line (about two inches long) and get a drill bit just a little smaller than the OD of the brake line and drill a hole in the CAT just after the flange and drive the piece of brake line into the hole. Then attach a hose to the brake line and run the hose up to a fuel pressure gauge. (most vacuum gauges have a fuel pressure section on the vacuum gauge.) You need to run this test quickly before the engine gets hot because the front part of the CAT will quickly get hot enough to melt any hose. At about 4500 RPM you should have no more than 1 1/2 PSI. If you have a lot more then that, the engine will run at idle and just off idle but will go flat when you try to go faster. This is just one of many possible causes.

You can lean out the carb too much, making it run hot but you need to check other causes first.

First get some of the dye that turns color in the coolant if you have a leaking head gasket. (available at most auto parts stores.) Confirm that the electric fan is working. Other things to test are the thermostat is opening and the lower hose is not collapsing when you rev the engine.

If you put the original SU pump in the front, it will give you problems because it is a low suction high pressure pump designed to be in the rear and push gas but is very weak on the suction side. If a pump is too high pressure, it can cause the float needle to be pushed open causing the float chamber to be flooded and too much fuel to enter the jet.

Let me know,
Howard