My brother-in-law recently had a 440 kit installed in his 2000 400EX. While riding it yesterday it began to ping pretty loudly and is down quite a bit on power. We had recently rejetted the carb, if that is any help. I am going to be tearing into it next week but would appreciate any thoughts on where I should begin my venture. Carb? Head? Valve Train?

Ken

 

"pinging" to me means detonation. Running a higher octane gas will clean that up. If you are going to tear into the motor do a compression test first. If the compression is low you know you need to pull the head.

 

what compression piston is it? what octane and brand of fuel? what jetting changes did you make and what is your carb set-up?

 

I did not do the origial work on the motor so I am not sure about the details on the 440 kit. I did change the main, pilot and needle. I dont recall what size, but it ran well for several days on 91 octane gas before the problem occurred. I have not ridden it so I cannot testify to the actual "pinging" sound but I have heard that 440's have a tendancy to stretch the head bolts and blow head gaskets, so that is where I was going to look first. Not knowing the proper compression ratio, it may be hard to determine anything from a compression test. Thanks for the responses so far.

Ken

 

TIMING CHAIN~~ i had the same problem! get a new one!! before you bend the valves and screw up your piston! i messed up the piston on my bike! sux but oh well! well i hope this helped

 

perhaps a little more research before tearing it down will answer some of this.

 

Running a 440 might require race gas or the use of octane booster to 91 octane fuel.