Topic: spark plugs/heat ranges

[carl550k]

 my 76 550k is running a mac 4/1 header with a uni foam filter.my plugs are a light gray color,no matter how the mixture screws are adjusted. i assume they are for slow speed/low rpm adjustments anyway. since i ride mostly highway high rpm , can i use a colder plug? i am an old hot rodder and most cars after installing headers, advancing the timing and using colder plugs are the norm. will this work on a bike?                 thanx carl

[eldar]

It is always something to try. An ICE operates on the same principles no matter what the application is.
Give it a shot but dont drop too low or go too high of course.  D8EA is the standard so D7 and D9 are fine.

[eldar]

Oh wait you have a 550. I dont know what your standard plug is, but going 1 up or down is still ok.

[TwoTired]

You may find that you will need to raise the needles or get needles from F model carbs.  Your plugs should be NGK D7ES (or A).  A colder plug would be the D8EA.  Try not to get the DR8EA (resistor plugs), as you already have resistors in your plug caps.

I did not like the D8s in my 550's, as they took way longer to behave properly during warm up.  Way worse in the winter, of course.
Cheers,