400 ex spark knock!!!! oil cooler

[crazyatvn]

OK last weekend at a race the temp was 97 and very humid. My 440 (stroked) ex was having some very bad spark knock. Never had this before. No loss in power and it ran fine except for the knocking noise. The noise was only present when you put a good load on the motor. But if you were not bogging the motor the noise was less or not there. My question is do you all think my head temp was to high? Do you think if I installed one of those secondary oil coolers that would rid my bike of this problem? Here is my set up!!

400ex ported and polished head, xr 400 HRC cam, 11:1 compression bore and stroke (piston was milled down a little to run pump gas), stock carb, WB pro-meg system.

I do not want to run race gas.

any other ideas would be great!!!

you might be lean try goin up a couple sizes on the main

[Sleeper]

You might want to try running a cooler plug and see if that helps at all. If it works it's the cheapest sollution. you might consider air scoops if you haven't done it already. Mine is stock and will ping a bit on take off after running the **** out of it on hot days and lower speeds. I think I am going to though scoops on it first.

Sleeper

[crazyatvn]

already have air scoops on it. Might try the plug thing. Any more ideas?

[TORO1968]

You might need to install a fully adjustable aftermarket ignition such as what MSD, Vortex, or Dyna offer. With this, you'd be able to back the timing advance off a bit, thereby eliminating or reducing the spark knock problem.

I'm running an MSD ignition right now, and so far, it's been a really good investment. All of the adjustments can be made right on the box, so a laptop is not needed. The one drawback is that the installation is somewhat extensive, requiring you to modify the factory wiring harness in several locations. Other than that, the entire system (which includes a 30kV coil) is pretty sweet. Can you say two-stage rev limiter??? :D

If you have any questions, let me know.

-Jordan

[ludester31]

hi,

where did you get your msd ignition and how much did it cost? I have a 05 400 ex that pings a little and the ignition would be a nice thing to upgrade.

[TORO1968]

I got my MSD setup from MPS racing (www.mpsracing.com). They had the best price out of anyone, just under $400. The ignition had to be ordered though, as they don't normally deal in ATV parts.

If you do a search for MSD, you'll see a bunch of my posts about the unit.

-Jordan

[TRXRacer1]

As said before spark plug is the first thing you should look at but you should have known that with 11:1 in an air cooled motor higher octains were going to be needed on those days when you push it harder.

[crazyatvn]

I did that is why I had the piston dome shaved down to lower compression. So it is lower thatn 11:1