Different Spark Plugs for VF500

So due to my retarded-ness I hydro-locked my motor with Sea foam and had to remove the plugs to get everything working again.
Since I had the plugs out I figured I might as well put new ones in.

The Plugs that were in the bike were: NGK DPR7EA-9

The Clymers manual states the following for Spark Plugs:
84-85 VF500
DPR7EA-9 for cold weather
DPR8EA-9 for regular conditions

1986 VF500
DPR8EA-9 for Cold Weather
DPR9EA-9 for regular conditions

All they had at the parts store were the 7EA's and 8EA's...I bought and installed the 8's since they were the happy medium between the three.

These are different heat ranges for the plugs...no?

Why do the different years ask for different plugs and how will installing a 7EA instead of a 8EA or a 9EA effect the bike?

 

The 86 engine is tuned different than the 84-85.

It has different valve lash specs, and different sized carbs.

Not sure how this correlates to a overall colder plug being used - but apparently it does.

 

Doesn't the higher number mean a hotter plug?

According to the Clymers manual the 86 bike requires the NGK DPR9EA-9?

I actually have the Owners manual for a 1985 VF500 and this is a page from it:

 

You would think logically the higher the number the hotter the plug, but it's strangely the opposite - as shown here.

http://www.ngksparkplugs.com/docs/tech/partnumberkey.pdf

 

Well what do ya know......

Ok...so I had a 7 in there before....a hotter plug (2 steps) to what the Manufacturer recommends....now I have an 8 (1 step) colder. But I should have a 9 which I cannot find anywhere

 

Running a 2 step hotter plug can result in detonation or pinging! 1 step hotter is not as bad - but yeah, you'd want to find a 9 hopefully.

Maybe order online ? Or check the dealer.

 

Carquest has them, or at least can order them for you, our local store doesn't stock them, but their nearest warehouse has 20, they can have them next day. Either tell them to run the number through interchange or let me make it easier for you and them, the current NGK number is: 5329

NGK has changed their numbering system (sort of) but they will have the DPR9EA-9 on the package and on the plug itself.

 

American plugs = higher number hotter the plug. European/Japanese plugs= higher the number colder the plug.

One step either way is not going to do much if anything. Unless you tightly tune your vehicle then it might make a difference. The big thing you need to know is what temps are you riding in. 100+ degrees all the time you might want the colder plug. Flat out racing would also want a colder plug. Normal temps from 40 to 90 and just driving around town/country you want the hotter plug.

You only need a plug range that will burn off all impurities and stay clean. Your environment temperature will dictate that.

You want to lean about plugs go here: Sparkplugs.com - Spark Plug 411 Also see the FAQ section.