Is this a jetting issue?

Here's the facts:

2000 YZ426F

About 4000 ft elevation,

About 60 Degrees out,

Stock jetting; 42 pilot, 162 main, stock needle, 2 turns out on fuel screw.

Bike runs really well.

I was climbing a sand hill, 3rd gear, half throttle. When I get to the top and stop, I notice a slight amount of smoke coming out of the exhaust. After a few minutes of running, not climbing the hills, there is no smoke. It only happens after climbing the hill, under obvious load, and goes away. Is this a jetting problem? Is it loading up while going up these hills and then burns off when run "normally" again? Or is there something else I should check out? Any input would be appreciated.

This IS an unusual event. The color of the smoke should be an indicator of what's going on. Blue smoke indicates oil burning. Black smoke usually points toward rich jetting. White smoke could mean that coolant is getting into the combustion chamber. Can you tell if the engine is running hotter than normal? Does it ping or knock when going uphill?

Doesn't sound like a jetting symptom.


The smoke is black. It does not ping or knock and I have not noticed it running any hotter. The smoke doesn't just pour out, in fact you can't see it very well if it is idling, but when you give it a little throttle there is a slight amount of black smoke that is noticeable. I have never noticed this before.


You say it doesn't sound like a jetting issue, is there anything else you could think of that might cause this? Is it cause for concern? Thanks guys.

Just burning out the carbon from your headpipe. Sand hills take alot of power and generate extra heat.

The jetting you described at mid-throttle is not too rich or too lean for this. If it were burning too much oil it would probably be smoky all the time.

Thanks James, I will not worry about it then, so long as everything else checks out.

You might consider trying some race fuel such as VP C-12, Sunoco standard(these are both leaded fuels) or maybe Sunoco GT Plus which is an unleaded fuel. There are other good quality race fuels as well. What I'm thinking is along the line of these fuels help the engine run cooler under severe loads and are great for this high revving engine. I've been using Sunoco standard for about a month now and swear by it.

Ant time you put the engine under load it will do time you see an old carburated car going up a hill or deisel truck they do this because it takes fuel to make power...........later.


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