Spark plugs, what brand and type are the best?

My personal preference for Harleys is Autolite Platinum (for Evo's AP4265)...stock ignitions, set to .040", aftermarket ignitions set to .035". Do not change heat range!!! Also make sure your plug wires are fresh, a rule of thums is to replace them every 20k miles or 3 years.

HD plugs ARE Champions, Champion has been making HD's plugs for over 30 years. Champion's center electrode material is too soft and erodes away too fast, as do the factory HD plugs.

The ONLY time I use HD's plugs are on the new Delphi Fuel Injected bikes, the factory HD plugs have a built-in "ion sensor" that detects engine knocking and pinging when the injection system's "ion sensing" (knock sensor) feature is enabled.

As for the truck, I can't really say, by past experience with Bosch's +4 plugs, on a dyno (on HD's), they provided no power gains whatsoever and they are quite EXPENSIVE. I have a 98 Chevy P/U with a Vortec 350 and run the Autolite Platinums in it also and have had no complaints.

How many miles are on your bike? What carb and ignition are you running? What jets are in the carb and where is the timing set? Are you running a VOES on the ignition and if so, has it ever been checked? If it is functional, it can be adjusted to a performance setting of 6 inches of vacuum, or you can buy one set to 6 inches. Also, have you checked for intake and exhaust leaks? Also again....."CHOKES" are almost non-existant today, today's carbs use enricheners, which DUMP raw fuel to richen the mixture for warm up. If you are fouling plugs with this, I will lay odds on it, that you have the ANCIENT gas guzzling S&S....forgive me f I am wrong. If I am correct, lift the enrichener lever fully up, twist the throttle twice and fire it up for about 10 seconds, close the lever half way for about 30 seconds, then push it closed and use the fast idle thumb screw to hold about 1500 rpm for about 2 minutes to let the bike warm up....you should never drive the bike with the enrichener on, and the rocker boxes should be hot before taking off. Cold take-offs are the number one reason for leaking base and head gaskets. Keep your hot idle set to 1000rpm!!!

EDIT.....ok, the stock keihin are notorious for long warm ups. Most likely the jetting in it is a 45 pilot jet and 175 -185 main, idle mixture screw should be around 2 1/12 turns outs. Using the enirchener on them is pretty straight forward, just leave it fully out for 2 or 3 minutes to warm up, in cooler temps it does take them a while, so I know what you mean by under 50 it's a BlTCH. Something that may help a little is to set the timing slightly retarded. The VOES must be hooked up and functional, they work best when adjusted to turn on at 6 inches of vacuum. Run the engine at 2000 rpm and set the front cyl advance mark in line with the front of the hole, which is about 32 degrees. Evo's don't need as much advance as HD gives them stock, they run a little better at 32.

If you have any more questions, just give me a hollar.

If it is fouling then it's likely that it is set too rich as most people tune their bikes etc to go balls out max hp at the expense of rideability. Plug brands are moot as they are all based on the same patent. It is nearly always incorrect application that results in people blaming a particular plug for poor performance. If your vehicles are in any way modified then it is likely that the stock plugs are no longer right for the application. Your local parts shop will have a book that lists reccommended plugs and in the front is an area that explains what the numbers and letters mean. This will guide you in choosing the right plug based on what's happening to the ones you use now.

The Bosch platinum's worked nicely in my '99 Ford E250 cargo van. It ran smoother and got a pinch more miles to the gallon than the old Autolite's I pulled from there. NGK's were all I ever used on my bikes, so I can't help you on that one. Sorry.

Autolite / Motocraft. tried all that fancy platinum kryptonite, split / multi electrode gobbledygook and its all gimmick. A well made standard plug is all you need for a stock / lightly modified engine.

NGK always runs the best for fouling.i run them in my harley and my sportbikes.i ran champions in them until i found out that they cracked at the case and insulator.oh and dont trust champion when they say they are american......they arent.

It is my experience that Champion plugs work the best on Harley Davidson.