04 Kx250 Pings With Fmf Sst Pipe...

[AARONA]

Was racing sunday and my stock pipe blew out at the seam just in the second 90 degree bend. Still not sure why. Bike was ripping though. Running 92 octane Chevron and Motorex Synthetic 2-stroke at 40:1, stock jetting. Put the SST on and the bike began to ping on the longer straits and uphills. I just let it ping and pinned it. Motor held together. But I am concerned.

Whats the deal? It wasn't pinging with the stock exhaust pipe (or at least I couldn't hear it) Can an aftermarket pipe make a motor detonate? Should I switch to race gas? I checked my top end out before the race, and it looked really good. No scratches or scrapes on intake or exhaust. I don't think it was pinging before.

Called FMF and they said they never heard of that before. The guy suggested race gas. I thought race gas was needed with high compression race engines, not exhaust pipes...

Anyone run into this before?

 

[marcusgunby]

Yes ssts are renowned for this problem-you have to run race gas or detune the engine to stop the detonation.

 

[AARONA]

Thanks Marcus. I was planning on race gas cause it would be easy to try...nice to get a second opinion. Wonder why FMF acted it was the first time it had been brought up?

I do like how it works. A little more power everywhere.

Good thing they haven't banned leaded race fuel up here...heheh!

 

[marcusgunby]

All companies deny any problem with a product(not just mx companies) untill they have a large backlash against the product-then they generally drop it,recall them or modify, luckily for you race fuel should fix it, here race fuel is not really available.I had one for my 03 KX133 and had to take it off as i couldnt stop the detonation without loosing power.

 

[Mr331]

Have you jetted up for the new pipe?

 

[AARONA]

ran avgas

So I went racing this last weekend and used strait 100LL avgas. It worked awesome! The bike was crisp and pulled hard with no pinging. I was happy. Plus avgas is only $3.05 per gallon. Race gas is $7. Super unleaded is $2.40...so avgas is a good deal.
It was a Alaska State Championship race in Fairbanks, Alaska. Forest fires had it a bit smokey out, so I didn't see in my manual how to jet for a 450,000 acre forrest fire burning within 30 miles...
Dusty Klatt was up racing with us...man is he fast!!