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Why the Smoke During Start-Up?

The Arctic Cat 800 H.O. engine

I received a question awhile back from ArcticInsider forum member, Dream of Green.

Q: When I fire up my 2010 F8 in the morning, it seems VERY rich and smokes heavily. It never fouls a plug. And once it is warmed up and “cleaned out,” it runs fine. I had a few guys suggest to me that the ECU was programmed that way to prevent piston scuffing on cold mornings.

What’s up… is this is the way it’s supposed to be?

A: According to one renowned engine engineer at Arctic Cat, the 800 H.O. is a bit richer (read: more fuel) at cold start-up. That’s just the way the ECU mapping ended up as the best compromise between cold startup and drive-away.

Here’s what’s happening: The smoking that occurs during cold startup is the remains of the heavy oil parts that collect in the engine after the previous hot engine shutoff. When the engine is shut down after the previous run cycle, the hot crankcase evaporates the light parts of the oil, leaving some heavy parts in the crankcase. When the engine sits long enough (usually the next day) to reach ambient temperature, then is restarted, these oil remnants are carried up and burned on initial cold start-up.

"Uncle" Al Shimpa shows fine form starting an M8

If the fuel map had been made leaner, it likely would produce a lean-condition bog at some temperatures and altitudes. And in fact, there have been some conditions (such as when the engine is cold and is accelerated up a slight incline) when customers have experienced lean bog.

Could the fuel map be better? Yes.

Like with anything… there’s always room for improvement. And the Cat engineers are always tweaking the machines to make them better, as detailed HERE.

Two-stroke fuel mapping is very time consuming, and there’s always a point where a compromise must be made between objectives that sometimes compete with each other.

And as our esteemed engineer said to me, future developments in areas like the oil injection system, fuel mapping and other areas will undoubtedly improve all aspects of engine performance, from cold start-up to fuel economy to oil consumption to horsepower to longevity to… yeah, you get the picture.



  1. Thanks for the info on the 800 HO, I followed the link to the TRF engineering test ride and saw the 800 EXT, did you get to ride it John? If you so what did you think about it, I spring ordered one so I’d be interested in your ride experience.

    Thanks, Vince

  2. Vince: Yep, I rode the F8 EXT there and later in West Yellowstone. In a nutshell, I think the EXT platform work very well… so much that it surprised me. In some ways it balances the sled better (definitely so with the heavier Z1 engine in that version of the EXT). A little less nimble and slightly slower cornering action, as to be expected. Ideal for big trails, big riders, big lakes, breaking trail on logging roads, and/or any combination of the above.

  3. I own a 2013 F-8 Sno Pro, it seems that the redesigned rear heat exchanger,differnt from the one last year, is not getting enough snow up to it to cool the system properly. My coolant light flashes alot on the trail, even when the trail has decent snow pack on it. I ride with buddys that have 2012 F-8s and they do not have a problem. I have to go off trail in deeper snow to get the light to go off, this is a hassle, please help, with i hope some kind of an update. Sometime i will be stuck running in marginal conditions, and i am worried about this problem. I dont feel that i should have to install ice scratchers to fix a bad design. Thanks


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