Enigine Knock

[2001EX]

Is spark knock on an 11:1 piston all the time if you dont run race fuel or is after you've been riding for about 10 minutes? I noticed after about 10 min. of hard riding the motor seems to knock a little under a heavy load. Is this a characteristic of a 400ex or do I need to run a 50/50 mix? Also, doesn't race fuel burn cleaner than regular pump gas?

[Ryan]

I would run 50/50 mix. It sounds like the regular gasonline is firing before the piston reaches its highest point.

Originally posted by Ryan
I would run 50/50 mix. It sounds like the regular gasonline is firing before the piston reaches its highest point.

Thats your first test and if the knock is still there then you need to do some tougher stuff.

Also determine that it doesnt do it with the r's up and just when lugging or pulling hard etc.

Hope the fuel clears it up otherwise it could get expensive.

[skemp]

If the higher octane fuel doesn't help, my bet is on a sloppy timing chain. They slap under a heavy load when they start to get worn out.