QuestionHello, I'm a new owner of a 72 MGB. I did a recent tune-up and and when I take it out for a run of about 10 miles it runs great. Then I let is sit for 15 minutes and take it out for another ride it seems to be sputtering when I give it gas. It happens in all gears and only happens after it sits for a few minutes.
Rick
AnswerHi Rick,
When a car came to me with that kind of problem I did a normal test sequence first. Compression test and if not great results I would adjust valves and run the test again. When I had a good Compression reading (135 to 180 PSI with little difference between cylinders) I then would proceed. (it is a waste of time to try to tune a bad engine)
I would test fuel pressure. (1.5 to 3 PSI) I had a scope at the dealership to test ignition but most people don't have that option so there is rough way to test ignition with only a timing light. Put the light on the coil lead not #1 wire as though you were setting timing.
On the coil you will see all cylinders firing and it just about like a steady light.
All of this is done in the first mode when it is normally running good. compression will usually not change from warm to hot running so you need to be looking at fuel or fire.
Now you need to get it into the failed mode and test fuel pressure and fire running on the road. How? by putting a "T" in the fuel line just before the carburetors and run a long hose out from under the hood and place the gauge under a wiper arm so you can monitor fuel pressure at the driving speed. (Be sure to put hose clamps at all joints)
Now place the timing light on the coil wire and run the wires out from under the hood and place the timing light under another wiper arm and tape the trigger down so the light is on all the time the engine is running. If it is a bright sunny day you may need to tape a piece of cardboard on the windshield over the end of the timing light so you can see the flash as you drive. I found that if you have a misfire in the primary side of the ignition or in the coil it can be seen in a flicker in the steady light as speed. It can not test cap, rotor, plug wires or plugs but it can be a good tool to test the coil and primary section of the ignition system.
Now drive the car and get it into the failed mode and look at fuel pressure and the primary ignition system when the car is running in it's failed mode.
If nothing shows up then you need to clean the carburetors and adjust and check all plug wires and the cap and rotor and clean or replace the plugs. The wires can be tested with a volt/ohm meter.
None of the tools are expensive and you can even get a compression gauge and timing light at Wall Mart and a volt/ohm meter at Radio Shack.
As long as you are going to own ANY engine powered anything, you can use these tools.
Howard
