So I've seen two differing plugs for my 76 DT400, some have said (articles and manuals not people), a B9ES and others say a B8ES. Which one is it or does it matter that much... Asking for a friend

B9ES for the 75/76 DT400 and B8ES for the 75/76 DT250. The B8ES is a hotter plug and the 400 runs hot enough already. Stick with the 9.

Thanks for the reply, that's what I thought but there's conflicting information out there so I thought I should check. Now I need to go buy the correct plug since I was given a B8ES when I went to a shop and asked for a plug. Thanks again!

I have a 1976 DT400. All stock and has a NGK B8ES and runs great.

Both the 75 and 76 DT400 Owner's Manuals in Tech Library say B9ES... not sure what other sources were involved but I've found owner's manual to be pretty reliable on stuff like plugs.

A "hotter" plug (B8ES) won't make it run any different... the danger is the plug tip could overheat during a hard run and turn into a "glow plug" causing preignition and engine failure.

(Spark plug heat range is a measure of how fast it sheds heat from the electrode/insulator... tip has to stay hot enough to burn off deposits but not so hot that it causes preignition)

I looked here when I searched for a plug. Guess I need to change it.

yamaha-enduros.com/index.php/plug-table

I'm not advocating you need to change the plug... even the owner's manual says you might need to go one range colder or hotter.

If you were doing hard full throttle riding or high speed freeway-type riding, the colder 9 would be a good idea but for normal riding around town and trails the 8 might be perfect.

I just ride around locally, no trails just cruising. I just ordered 2 new plugs. I guess I'll keep them for spares.

The sources I've found are here on our site, not faulting anyone here but as I said before some say B8ES and others B9ES and when I went to a dealer to get a plug they gave me a B8ES. I'll go with the B9ES to be safe.

Thanks for all the replies. Tony