I couldn't help but notice the number of recent posts on mid-range burndowns. Having had this happen to me more than once already, I am still very paranoid of running my machine at part throttle.

Reading the posts and comparing the data, it has seemed to happen to numerous machines from completely stock form to nearly race ready and about everything in between. Machines with HSP, RCR and HPD parts. Stock carbs, bored carbs, and flat slides. The data would tend to make me believe there is potentially a fundamental flaw in the engine design, since no one specific aftermarket part seems to induce it. Basically, just a higher power level than stock. One other thing I noticed was it seems to be 99 machines and newer, but that could be just what everyone is modifying now.

So, please post if you've had a mid-range burndown (i.e. @ less than half throttle). Please tell what year your machine is, what mods you've done to it, and what you did to prevent it from happening again.

I'll start: Mines a 1999 Scrambler 400, HSP pipe, HSP Head, HSP Clutch kit, Air box mod, 38mm TMX carb. The first burndown was with the Stock carb and a UFO. Second burndown was with the TMX. Seems fine cold, but sounds like pinging only in the midrange when warm. Currently went to a 54 Jet Needle, but still don't trust it.

Thanks for any input, hopefully the information will help others.

Jason

 

Scramblin,

I had a WFO melt down on mine, but I've never heard (until recently) about a mid range burn down. The fact that most people don't have them makes me wonder. My Sport is modded to the max and, with the exception of the one melt down, haven't had trouble yet.

I have two words for all of the burn downers there, SWAIN TECH. I had my Wiseco piston ceramic coated on the top and "Poly-Moly" coated on the sides. Absolutely ZERO problems with it.

Also to all you who modify your 400s and DON'T use Wiseco pistons, you have my sympathy. Wiseco pistons are softer that the standard cast pistons which means they will be less likely to break than the harder cast pistons are. This is the main problem with the stock pistons, and why my dealer will only replace a stock piston with a Wiseco.

 

I just fell victim to a Mid Range Burn Down on Friday the 6th of April. I was riding at about 5,000 to 6,000 RPM at very low throttle position, and had the engine shut off on me more than once. I pulled the plug and saw that it was colored a dark grey with lighter colored specks. I knew that the piston wasn't going to make it... It ended up giving up the ghost a couple of moments later. I had to push the quad up the ramp into the truck all by myself, good thing I had my Wheaties for breakfast !! LOL Even in the face of adversity, never lose your sense of humor !

I tore the engine down Friday night and called Rick Ritter on Saturday and discussed the problem. Low throttle opening and fuel flow doesn't give enough cooling and lubrication for long, high speed runs, fire roads, dry lake beds etc.
I may have to look into a EGT gauge before I barbeque another slug.

 

Why is everyone talking about meltdowns as of late?!?! I am definately going to do some jetting checks next ride!

With a midrange meltdown...do you just pop in another weisco and ready to go?

 

Dumb question: How can you ride long, high speed runs if your on a low throttle opening? Did I miss something here?

 

Hey Captin Did you envoke the power of the yeti To push it into the truck?

 

Xplor, after reaching the desired cruise speed, backing off of the throttle is normal, as it takes less power to maintain speed than to accelerate to that speed.
Dazed, I suppose that it was the "Power of the Yeti" ( and I thought that no one caught that jewel of info. The boss's daughter wonders why I wear a sweater under my T-Shirts during summer ). Or just being PI**ED OFF at vaporizing a piston. Bill Bixby has nothing on me ( For the kids, Bill Bixby was the "Incredible Hulk" on TV in the late 70's / early 80's ).
I would like to think that the 4+ lbs that I removed with aluminum sprocket and disk brake guards that allowed me to push it up into the truck. That's my story, and I'm stickin' to it !!!

 

>>>Xplor, after reaching the desired cruise speed, backing off of
the throttle is normal, as it takes less power to maintain
speed than to accelerate to that speed.


I've tried this on my Arctic Cat Pantera, but it won't work. The driven clutch "back-shifts" so well that my machine won't do it. It instantly adjusts to throttle input. No offense but is your driven clutch not backshifting?

But anyway... before the melt down had you done any adjustments to the mid-range circuit of your carburetor. I.E. the changing of the clip on the needle jet?