Triumph Repair: Carb backfire, charcoal canister, vent hose

Question
I recently bought a 77 spitfire and the car ran great for about a month. However, it has always puffed a fair amount of black smoke out of the exhaust and runs rough at idle as well as hesitates and backfires under load. I changed out the plugs and wires and realized the plugs were black as night. I also static timed the engine but have not been able to put a timing light on it. It seems to be backfiring through the carb (single stromberg 150CD). Is this a timing issue or is there a more serious issue. I thought it could be the mixture was to rich so I leaned it out through the damper hole with the proper tool. it does not seem to help.

Answer
Hi Mat,

The black smoke and the flat black plugs come from only one thing and that is an excess amount of fuel entering the engine. Since adjusting the mixture with the 3mm Allen wrench did not correct it, then it is most likely either a flooding float chamber or the auto choke is at fault. There is one other item that can do it and that is a torn diaphragm on the carburetor piston.

First remove the float chamber hose that runs from the float chamber to the charcoal canister and shack it to see if there is any raw fuel in it. If there is then it is a flooding condition and you need to remove the carburetor and check the float needle and seat and float level.

If there was no drops of fuel in the vent hose, remove the top of the carburetor and inspect the diaphragm for any holes or damage.

If the diaphragm is good remove the three screws on the outer edge of the water chamber on the choke (don't remove the bolt in the center)
This should expose a short lever that you can manually move in it's slot in the plastic cover. This is the choke lever and when you start the engine you should be able to manually control the choke on and off.
As I remember counter clock wise takes the choke off.
When you put the three screws back in the shorter screw goes in the bottom hole.
If up can correct the running by manually moving the lever, then you need to examine the coil spring that fit onto the end of the lever to see that it is not broken and confirm that coolant flow is traveling through the coolant chamber to operate the spring coil which moves the lever when hot.

One or more of these three items should be the problem. After you correct the problem you will need to readjust the mixture needle with the 3mm Allen wrench which you tried to adjust to correct the problem.

Howard