Triumph Repair: stromberg carb, bright sun light, pencil lead

Question
have a 1980 spitfire 1500
the only to start the spitfire is to lift the needle and it runs very rough any suggestion thank you

Answer
Hi Robert,

I often received cars that run rough when you change something like lifting the pin under the edge of the top. That may or may not have anything to do with the carburetor.

To diagnose a running problem I had to start from scratch and run a series of tests and the tests had to be done in the correct order. There are only three things that an engine needs to run correctly and they are, Compression, Fire and Fuel and they must be tested in that order.

Compression -- I would not attempt the correct any running problem until I ran a compression test. The compression test must be done with the throttle wide open and at least 5 or 6 revolutions of the crankshaft. It must read from 135 PSI to 170 PSI on every cylinder and very little difference between cylinders. If you don't have that, it is a waste of time going any further. (remove the wires off of the (+) side of the coil before spinning the engine to ru the compression tests.)

Fire -- (Ignition) Best test is with a scope but most people don't have a scope available. But you can still do most of the testing with almost no tools other then hand tools. Remove all four plugs and attach each plug wire to it's spark plug and lay the plug on a metal part of the engine. (Put the wires back on the (+) side of the coil) Have someone spin the starter and watch the plugs spark. The spark should be blue in color and thick as a pencil lead. (not in bright sun light) If the spark is hair thin and yellow or orange in color it is a weak spark.

If the spark looks good, set the ignition timing to specs and examine the distributor cap inside and outside for any signs of carbon tracking from any pin. Now remove the coil wire from the cap and hold it close to the center of the rotor and have someone spin the starter and try to jump a spark to the center of the rotor. If you can jump a spark to the rotor, it is for sure bad and must be replaced. Test the plug wires for their resistance using an ohm meter. You should see about 5 K ohms per foot of wire. (usually a bad wire will show no connection at all)

Now if all of that is correct and only if that is all correct can you look at Fuel as a cause of your problems.

First test of fuel is to spray starting fluid (available at any auto parts store)into the intake as you have someone try to start the engine. If it starts and will only run if you keep spraying starter fluid into the intake, then you first need to test fuel pressure at the fuel line on the carburetor. It should be from 1.5 PSI to about 3 PSI and no more or less. If it has that, remove the four screws in the top plate and examine the diaphram for any holes. Then if that looks good, gemove the piston and look at the long metering needle and be careful not to damage it. The top shoulder of the needle should be slightly recessed in the bottom of the piston and it must be loose as if mounted on a spring.

On the compression test, if you found the spark plugs wet you may need to examine the auto choke mounted on the side of the carb. (these are very prone to fail) They can fail by over choking and thus flooding the engine or they can fail by supplying no extra fuel for starting.

If all of this checks out correct so far, You will need to remove the carburetor and check the float level and needle and seat for the float and confirm that there is no water or trash in the bottom of the float chamber. Also check the vent hose from the float chamber to see that it is clear. (a good test of it is to remove it from the carburetor and test run the engine)
Also unscrew the top center cap and lift it up about an inch and push it down and if it has hydraulic resistance it is ok but if there is no resistance be sure to add a few squirts of engine oil in the top.

Somewhere in all of this you will find your problem. Don't skip any part of this. Let me know.
Sorry, I have no clue what you meant by "the only to start the spitfire is to lift the needle"

Howard