Spark plug question

**Odin** · 5th August 2005, 10:02

I have just changed the sparkplugs in my xv500 but could not get the same pair as I took out. I had a set of BPR7ES and replaced them with BP7ES (so no R) The person at the shop said I'd be ok and since the price isn't all that bad I decided to go with them.
But I am quires as to what the R stands for and perhaps the other letters as well.

Guess I should have been at the workshop but I had to work

**vifferman** · 5th August 2005, 10:09

Originally Posted by Odin

I have just changed the sparkplugs in my xv500 but could not get the same pair as I took out. I had a set of BPR7ES and replaced them with BP7ES (so no R) The person at the shop said I'd be ok and since the price isn't all that bad I decided to go with them.
But I am quires as to what the R stands for and perhaps the other letters as well.

Guess I should have been at the workshop but I had to work

"R" means it has a resistor in the cap (which as far as I know, the only purpose of which is to reduce radio interference or summat...)

**Odin** · 5th August 2005, 11:18

Thanks, so no preformance influence at all.... good to know

**FROSTY:Me** · 5th August 2005, 11:25

every letter and number means summaat --Definitely it will not affect your bike --the R does designate resistor -for radio supression

**TwoSeven** · 5th August 2005, 11:57

You had a plug with a 21mm hex, projected insulator, resistor, medium temp, 19mm reach, 2.5mm center electrode.

Hex, is the bit you put your plug spanner over.

The insulator sticks out a bit

6 is halfway thru the heat range (hotness 1, coldness 12) it refers to the plug tip temp with 12 being about 450C and 1 being about 850C. I've lost me little book that had the actual temps in it

The resistor stops radio frequency interferance, which means everyone with a car alarm is now going to love you heaps - not really a problem for your bike, but a modern one with a modern CDI will require one of the resister plugs.

**vifferman** · 5th August 2005, 12:01

Originally Posted by Odin

Thanks, so no preformance influence at all.... good to know

In fact, on one of the VTR1000 forums (or maybe more than one), there are guys who swear by taking the resistor out of the sparkplug cap/lead, and replacing it with a brass rod, as it gives a "hotter, fatter spark". Made no discernible difference when I tried it, so I put it back. Iridium plugs made no difference either, that I could notice. :spudwhat:

**Bartman10** · 5th August 2005, 12:08

Originally Posted by vifferman

Iridium plugs made no difference either, that I could notice. :spudwhat:

Iridium plugs last longer, but won't give you much of a performance boost on a low reving engine such as a VTR1000. If you've got a high rever, eg CBR250, ZXR250 etc they're a good idea.

**onearmedbandit** · 5th August 2005, 13:41

R means racing, F1 cars use 'em. S means slow, Honda's use them.

**Odin** · 5th August 2005, 13:46

Originally Posted by onearmedbandit

R means racing, F1 cars use 'em. S means slow, Honda's use them.

...and E means Economical and fiats use them ....

**TwoSeven** · 5th August 2005, 14:16

Originally Posted by vifferman

In fact, on one of the VTR1000 forums (or maybe more than one), there are guys who swear by taking the resistor out of the sparkplug cap/lead, and replacing it with a brass rod, as it gives a "hotter, fatter spark". Made no discernible difference when I tried it, so I put it back. Iridium plugs made no difference either, that I could notice. :spudwhat:

Thats the plug cap resister not the plug resister. If you swapped to a non-resister plug on an EFI or CDI bike you may find it starts missing or firing incorrectly. The RFI messes up the circuit with a bit of dodgy feedback.

Good plug-caps that are correct for the bike have sound contacts and dont mess up the timing.