YZ400 Hotter Plug

I was wondering if anyone could tell me a hotter plug that I could use for the YZ400. Stock is a CR8E.



I hope no one does. 8's are hot enough. An EK may not foul as easily. Some prefer the Iridium plugs. But don't go hotter.


I agree with mark, i don't know if it hurts to use a hotter plug but If you want to there is a cr7e. Try the cr8ek, it works good and doesnt foul near as easily.


98 yz400

[ May 21, 2002: Message edited by: strack ]


I got some bad gas Monday. Ego will comment on that in a minute. Anyway, Monday evening I went through two plugs (CR8Es). They fouled black but different than rich fouling. Looked like flat enamel black.

I picked up a box of CR8Es before going riding last night (upcoming group ride). While I was there, I got a EK and EIX(?), just for grins. The new CR8E lasted about three laps (1.6 mile laps), the first one was an observation lap. Then I put in the heavy iron, the CR8EIX(?). It lasted probably 5 laps. Then I put on the EK. I ran hard about 2 1/2 hours (ran through the rest of the tank of gas, at least down to reserver, that's a lot of riding) and it's still in there.

I am overlean just to prove a point. 162 main, 35 pilot, FHN#3. The fouling was not rich.

In fairness, mostly on the EK, I was cutting the lower part of the track where I was harder on the gas (practicing changing attitude in air over a big but safe tabletop). That may have been the determining factor. But 8E, 3 laps. EIX 5 laps. EK energizer bunny.

Good luck,


I use a CR8Ek and they work great, I haven't fouled one in awhile.

Somone Say "BAD GAS" :D

Unless ya want to burn a hole in your piston you should not place a hotter plug into the bike....

Long term this will damage and eventually burn a hole in the piston (IF YOUR JETTING IS TO LEAN).

Again, I dont understand why I see so many people with plugs just giving up the ghost. I have had two plugs in my 00 Since I have owned it in Jan of 02. I replaced the first becouse I just wanted to no reason. Now that plug is in my sons 02 250f running fine...

I think the suggestion of "BAD GAS :D " may be valid, I have never gotten BAD GAS, Well Except when I eat at That TacoRia before I ride :)

Thanks Mark for starting me up :D


A hotter plug (CR7E)is an effective option for combating plug fouling and will work well if you're riding in conditions that don't allow sustained wide-open throttle: woods, trails, tight mx tracks. I have run a "7" extensively with no problems.

WARNING: If you opt for the hotter plug and take your bike to the desert, flat track racing, or long fire roads--any place where you can keep it pinned in 5th--you risk melting a piston. This happens when the high combustion temps turn the CR7E into a "glow plug" which initiates destructive detonation/preignition.

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