Magneto malfunction??

[johnnyd]

Pull the valve cover on that low temp cylinder & check the valve lift.
Borrow a BoreScope & take a look inside.
As a last resort, you may have to pull the jug & look for signs of wear on the cam/lifter.

[Bill Greenwood]

I would try simple before pulling valve cover or certainly a cylinder.
Can you isolate one cyliinder? Run engine from cold for about a minute on bad magneto. Then carefully feel for the cold exhaust pipe. If you find one concentrate on those components.
Id also number plugs for each cylinder as you pull all plugs. Examine each one for a minute crack, hard to see some and for any speck or carbon fouling. Id also test each plug on a Champion plug tester to make sure plugs fire under pressure. Even new plugs can be bad and someone may have dropped on along the way. You can also swap all the plugs from odd bank to even bank to see if problem changes and follows the plugs.
Problems like valve lift or cams lobes are less likely because they are not going to be less or more when running on one mag or the other, and they dont occur overnight.
A general check of ignition systems is if the engine starts right away when cranked. The other end is when running at max rpm if it doesnt misfire, which is harder.

[dondday]

Again, Thanks for the responses. All suggestions sound good, but must restate. If all your suggestions for misfire, missing, backfire are caused by worn cam lobe, improper valve clearance and other issues related to individual cylinders, would the symptoms not be noticed when selecting the right mag as well. Remember, right mag operation is normal.

[Bill Berson]

When you replaced the switch did you get the p lead connected to the wrong mag?
You may have replaced the wrong mag?

[dondday]

P-Leads in correct mags.