Triumph Repair: Weber conversion, degree thermostat, poor combustion

Question
I have a 1980 Spitfire.
I recently replaced the ZS carb with a Weber DGEV, and at that time I also replaced the sparkplugs.
It ran good all summer, but this fall when I replaced the sparkplugs I found that the sparkplugs were black & sooty.
They were never that way when I had the old ZS carb on the car, so I assumed the mixture was running to rich.
I called the place I purchased the carb & manifold from (Pierce Manifold.) They said they new of a couple things that would help my situation, but I am not certain if there suggestions are things that are wise to do.
They said that it would be best if I could get that engine to run a little hotter than the 180 degrees it was originally set up to run. I thought that I could accomplish this by replacing the 180 degree thermostat with a 195 degree. Will it harm the engine to run a winter thermostat (195) in the summer?
They also said that I should change the ignition timing from the present setting of 10 BTDC to 16 BTDC. They said it would not damage the engine as long as I did not hear pinging from the engine during acceleration. Is that OK to do?
I already replaced the primary idle jet with the next size down, but I can not go any smaller and still stay within the carb specs.
I really believe the poor combustion is due to the manifold design, but I can not imagine that everyone that is using a Weber downdraft is having the same problem.
Can you shed some light on this issue for me?

Answer
Hi Ed,
I agree with some of what they say but not all. If it is running rich changing the temperature that the engine runs at is not a good way to correct a rich mixture. While advancing the timing (just short of detonation) will improve performance but still not correct an over rich mixture.
Any time any engine is altered it does change ALL of the settings necessary to run correctly.
Running a 190 degree thermostat in the winter will be an advantage but will be dangerous in the summer.

First you must determine if it is rich or oil on the plugs and that the correct heat range plugs are used. Also that there is not just something wrong with the carb. Like float level too high, float chamber venting not correct, Rich at what RPM? Find someone or a shop with CO/HC equipment and have the engine tested at several RPM ranges to get a picture of what is really wrong and go after that instead of trying to diagnose by symptoms.

Before you have it tested run a compression test (a dry and a wet test) If the dry test is off a little set the valve clearance and test again. Then run a wet test (or a leak down test if you have leak down test equipment) and if it fails the wet test or the leak down test you are wasting your time with everything else until the engine is fixed. Don't skip this because you don't want it to be an engine problem.

Run a intake manifold vacuum test at idle and at full throttle full load. So you don't get a speeding ticket find a steep hill and accelerate up the hill at full throttle in third gear and watch the vacuum gauge. You should never see anything below 5 in hg at full throttle full load.

Set the ignition timing to specs or you can advance the ignition a little at a time (with a hot engine) until you get a pinging by a quick throttle opening from idle or under load at a low RPM in a higher gear. When you arrive at the timing that you get pinging note that timing and retard by at least 4 or 5 degrees and consider that as your upper limit. keep in mind that the Pinging you hear is detonation and it will quickly destroy an engine if allowed to continue.

Howard