Triumph Repair: Spitfire MK 4 72 - 1500 - Misfire, spitfire mk 4, bright sun light

Question
I have just purchased a Spitfire MK4 1972 fitted with the 1500 ...... Engine sounds great , it's had alot of work done but has been garaged for 6 months. First drive out and at 3000 revs approx it has a small fluffing/ misfire which holds back the power ??

Head gasket , ignition or is running rich a possible .... Idels at 1100 revs and smells quite rich ..... If you rev the engine with no load it revs fine with no splutter ???

Any thoughts , many thanks ........... Buddy

Answer
Hi Robert,

Although symptoms can suggest a direction to start looking, generally symptoms are for the most part useless for diagnosing. Testing is the only method of finding a problem.

If your car was brought to me in a dealership I would have to use a procedure of testing.

First I need to know that the engine is good. (Even if it is a new car or a fresh rebuild)
This is a simple test. Run a compression test. (throttle open) and give me the results. (compression gauges are not expensive and can be used on any gas engine)

Ignition must be second. Even if you do not have access to a scope, there are simple rough tests that will work. First set the Ignition timing to specs. (This is very important, don't skip over it) When you have the plugs out doing the compression test you can connect each plug wire to it's spark plug and lay each plug on any part of the engine so you can see the plug gap. Then have someone spin the engine and watch each plug. The spark should look blue in color and be thick as a pencil lead. (don't do this in bright sun light)

Fuel is last. when you revved the engine from idle after warmed up do you see black smoke out the tail pipe? and when you pulled the spark plugs, were they covered with a fine flat black powder that was easy to wipe off? These are clear indicators of a rich mixture.

1100 RPM idle is too fast but should have nothing to do with mixture. What carburetor/s do you have? dual SU or single or dual Stromberg?

The reason you must establish that the combustion chamber is good (compression test) and that the Ignition is correct is that they affect the adjustment of the carburetor/s so they MUST be correct before you attempt to adjust the carb/s.

Let me know what the compression test was and that you have set the timing and I will guide you through the adjustment procedure.

Howard