Its an HSR 42.

 

Forget about spark plugs curing the problem, you need to set up the carburetor.

HSR 42 Tuning Manual

 

And use NGK plugs. Champion plugs have always been a problem for me. Opinions may vary. Ken

 

The brand of spark plugs has nothing to do with the op`s issue.

Champs have never been a problem in any engine I have owned, or any of my friends engines, for 50 years so far...

 

Like I said, Dan...opinions may vary. Champs have never been my favorite...for over 50 years. No biggie. Ken

 

Autolite plugs. Champions suck.

 

I wonder if something else is going on here, like Dan I've been running Champions in my shovels and evos for years with out a problem, but I've seen here and in the past a lot of people are adamant about Champions being junk? I'm just wondering if it could be other things, brand and type of ignition module, brand and type of plug wires, brand and type of coil, or unproperly adjusted carb? I run stock ignition parts or Screamin' Eagle and I spend a lot of time making sure what ever type of carb I'm using is dialed in

 

Turned against champion plugs when I was into BSA's. '68 650 bored .60 over, cammed and stroked. Could not keep champions in it for a week, they would die on me. So tried NGK. Ran very well . That convinced me NGK was a better plug, so I've stuck with them since 1971. As I've said, opinions vary, and that's fine. Ken

 

I agree with you Ken I also like NGK plugs, I've used them in Harleys with out a problem, were I found the NGKs excelled is in two strokes, my two stroke bikes and snowmobiles I experimented with lots of plugs over the years all I use in them is NGK, but in my Harleys I'll use Champion or NGK they both have worked well in any of my Harleys

 

I spent a lot of years drag racing inline 4s, Jap bikes, tried every plug around at that time, and NGK was always what I came back to.
NGK Spark Plug Heat Rating
The heat rating of each NGK spark plug is indicated by a number; lower numbers indicate a hotter type, higher numbers indicate a colder type.
Champion ® has a spark plug for your engine. ... The higher the number, the hotter the plug, and the lower the number, the colder the plug.