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BASSic

Overheating and Running Lean?

7 posts in this topic

I went on a nice ride this past weekend and rode some very technical trails. Now in the middle of the summer with no rain, these trails are difficult. This past weekend, I went and rode them after it had snowed/sleet, rained on top of that, then gold cold overnight. There were slick icy/snowy patches all over the place.

In one particular section I had a hell of a time getting up a steep slick section. A worn rear tire combined with the tall seat height and tall gearing of my YZ426 didn't help either. I spent about 30 minutes getting up a very technical rocky hill (it's difficult even without snow), and at one point my bike spewed some coolant out the overflow and started running like crap. It kept stalling, sputtering, and backfiring which didn't help getting up the hill.

Being relatively new to liquid cooled 4 strokes, are these symptoms of overheating? Is the bike running lean when hot? After I finally made it up the troublesome hill and started moving again, it ran much better.

When I made it down the other side of the hill, a pack of quad riders my brother and I chatted with couldn't believe that we were crazy enough to ride bikes in those conditions.

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Basically YES, you overheated it and you started having problems associated with the extra engine heat. If you plan to ride conditions like that often then you may want to consider a coolant catch tank so you don't blow all your coolant on the trail. Also, using a performance coolant like engine ice or even adding a little water wetter (made by Redline) will help keep you a bit cooler in those conditions.

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Another contributor here is the weather. Lower temps result in denser air, which begs richer jetting to compensate.

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the fact that you were struggling up a hill will make a bike over heat. when the bike gets overheated it is actually running richer. overheating in those conditions is somewhat normal . when your over heating starts to degrade performance (running like poo, stumbling) you need to stop and let it cool, its trying to warn you, its telling you to stop. its not good to push an overheated engine of any type/size/displacement whatever.

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Another contributor here is the weather. Lower temps result in denser air, which begs richer jetting to compensate.

I considered that, but why would did it only run like crap when I overheated?

I just learned from the previous owner that he never rejetted after putting an aftermarket pipe on it. Top that off with 40 degree air and I can only assume that it's way too lean. Surprisingly it doesn't feel like it though. Even in this cold weather the bike seems to run fine - lots of power at all RPMs, no bog, no sputtering, and no backfiring.

The catch can is on my list of things to get before the end of winter, along with radiator braces, a skid plate , and disc guards. Is it possible to rig something up myself, or would I be better off just getting a catch can from a WR?

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I considered that, but why would did it only run like crap when I overheated?

I just learned from the previous owner that he never rejetted after putting an aftermarket pipe on it. Top that off with 40 degree air and I can only assume that it's way too lean. Surprisingly it doesn't feel like it though. Even in this cold weather the bike seems to run fine - lots of power at all RPMs, no bog, no sputtering, and no backfiring.

The catch can is on my list of things to get before the end of winter, along with radiator braces, a skid plate , and disc guards. Is it possible to rig something up myself, or would I be better off just getting a catch can from a WR?

The weather-related lean jetting wouldn't cause it to run that bad, but it's an aggravating factor, and may have been part of the reason it got that hot, and/or why it misbehaved so badly when it did.

And not all aftermarket pipes require significant rejetting. The DRD 's I currently use work fine with the same jets I ran with the stock exhaust. OTOH, pipes with larger muffler core than the original pipe may actually make the bike run rich.

A catch can cab be any container that you can run the overflow into. In order to recover the coolant, the hose has to reach to the bottom of the can, though. A key element of coolant recovery systems is the cap. The cap needs a seal at the top of the radiator neck to prevent air from leaking in when the vacuum formed by the cooling of the system is trying to draw coolant back to the radiator. You may need a cap from a WR.

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And not all aftermarket pipes require significant rejetting. The DRD 's I currently use work fine with the same jets I ran with the stock exhaust. OTOH, pipes with larger muffler core than the original pipe may actually make the bike run rich.

It's a Thunder Alley Pipe. From what I read, they need a bigger main jet. With stock jetting, my bike runs great even with cold air at relatively low altitude (900 feet). The low end and midrange power and throttle response is incredible. The top end seems to be lacking, but this may just be my perception coming off of a 2-stroke.

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