We got it figured out! It turns out, that when our engine guy put the cam bolts on, even though he used loctite (it may have been the wrong grade/color, but were not sure), he forgot to clean the bolt holes of oil, so the loctite had nothing to hold to. So anyway, we cleaned the bolt holes, reloctited, and retorqued the cam bolts. Topdawg, this may be the same problem that you are having, because if these bolts work loose, it will cause MAJOR engine damage (bent valves ect...)

 

250rampage,

It's good to see you fixed your problem. Nice to hear. I have another question if someone can help me with it.

Gabe, you told me 110 would be overkill. Would I be able to run 93 Premium w/Octane Booster and it be safe? I was told that if I didn't run the proper octane gas, I would get carbon build-ups on the top of my piston, and I would have problems. I want to run the lowest octane I can run, and everything still be safe. For example, if something like 98 or so would be safe, I wouldn't want to run 110(overkill) or 93(not enough). Hopefully you understand what I'm saying, because gas is not cheap. I ride aggressively, and practice on the MX tracks very often. What do you suggest for me? Your input is GREATLY appreciated. Thank you.

 

It sounds like we do the same type of riding, and with my setup, I'm using a mix of roughly 65% Premium to 35% Race gas. I would probably use less race gas and more premium, but my dad has 2 drag cars, so we always have some very-high test fuel here. 11:1 seems to be the border line for the xr400 series motors, but there are too many veriables to say anything for certain. I think that premium with a quality octain booster should work...but just keep an eye out for detonation.

 

I've talked with quite a few that report that 11:1 is fine on pump premium. There are many factors that come into play, but that seems to be the where the limit lies.

The lower your altitude, the more octane you'll need. Personally I ride from about 700 feet to about 1400 feet.

I wouldn't be too worried about carbon buildup, crappy gas will lead to it, running rich, and so will burning oil, but that's a gradual process that takes some time. The thing to watch for is detonation. Detonation is destructive to your engine. It will be a "pinging" noise upon heavy acceleration. Some detonation is inaudible, but the most destructive type, you should be able to hear.

Like I said before, I personally believe mine would be fine on straight premium (JE 10.8:1), but sometimes I really push it in a race - and if something happens that puts the engine under a lot more stress, for instance: I am in the lead with a lap to go and I get a flat tire - I don't want to worry about detonation. I've actually had this happen with the stock engine & 2 flat rears in the heat of July at a race, and got some pretty severe detonation & had to back way out of it.

Also don't run any ignition advancing devices, like advance keys or CDI boxes that supposedly advance your timing - this can lead to destructive preignition.

Experiment around a little - if you hear detonation, don't push it and get some higher octane fuel. I'd say either a 50/50 mix or a 30/60 mix of pump and 110 race would be more than enough octane to satisfy your engine's requirements & if you don't plan on really abusing it, pump premium will probably be fine.