Carb sync question

[DomP]

So if I get 5-10 miles on it then hit the kill switch and get the plugs out

[McCabe-Thiele (Ted)]

I hate repeatedly taking spark plugs out as once you have fitted them correctly and the sealing washer has flattened that should be it until it needs a plug change. I'm also a tad paranoid about stripping a plug thread on alloy heads.

In my youth it was advised to change the sealing washer if a plug was removed for cleaning at a first service and put back in. You could buy replacement loose washers. I think it was also advised in the leaflets that came with spark plugs back in the 1960s. I'm remembering here that four spark plugs were less than a £1 back in the 1960's.

I am guided more by how an engine runs - does it idle okay, is the acceleration smooth without obvious flat spots when it's "on Cam" the colour of the exhaust pipe after a decent run, is the exhaust cold or hot at idle.

Since I rebuilt my 400 engine I have not removed the plugs as I'm happy with how it runs. My 500 is a different story so I am reading your posts with interest. I'm seriously thinking about replacing the four slow running jets before I put the carbs back on as I do not know for sure how many bits of wire might have been poked inside them - they are all stamped 40 iirc.

[K2-K6]

So if I get 5-10 miles on it then hit the kill switch and get the plugs out

The miles should clean out combustion, allow it to reach full running temperature, and clean any fouling from the plug surfaces to avoid giving false perception after cold start etc.

Kill switch routine is ordinarily when you are checking fully loaded running at big throttle opening and hard on torque demand. That entails pulling it hard with substantial throttle, running up fully on main jet at maximum demand conditions to asses the mixture under those circumstances. Valid for those reasons as you want to suspend running right at that maximum demand to get the most accurate picture of the prevailing combustion conditions.

  It's not for this scenario of general setup and checking if the very low speed system of jetting is accurate.  A simple run out to get it fully warmed etc is just fine to build a picture.

I don't routinely replace plug washers, always use a light smear of copper type lubrication on threads, and lightly tighten. Never have any leaks or compromised threads in practice.