790 cold starting

[Muxster]

While starting my 790 this fall (I purchased it new this past summer) I observed an interesting phenomena. Down to about 50 degrees it starts normally with a fair amount of blue/gray smoke closer to 50 while its warming up. When the temperature is below about 50 it still starts easily but it automatically throttles up to 1400 rpm for 60 seconds then throttles back to 1000 rpm (where it was left when shut off the previous day). Also the exhaust has almost no blue/grey smoke and has a "harder" tone during this initial period. When it throttles itself down the tone is "softer" until the engine starts heating up. Its as if there is a controller with temperature sensor that changes the injector duty cycle to lean it out or something to allow it to start on cold fuel. Has anyone else observed this? Is this normal?

The engine always starts easily and I have not had to use the heater position on the switch. It doesn't get to freezing (very often) where I am so I may not need to use the thermal start feature. Or should I be using the thermal start feature even though it always starts right up?

 

[farmerjim]

mine seems to do the same thing its a 2005. i think its normal for that motor. i use the thermal start in the winter when its below freezing, have also tried it above freezing and i don't think its any different. it will sometimes idle up longer i think depending on the temp.

 

[2kpsd]

Mine does the exact same thing - I'm pretty sure it is normal. When cold it really clatters on first startup with or without using the heater position first. Mine only does this when the temp is cold though. It's been 30-45 degrees here for the past few weeks or so. Smoothes right out after idling a little bit.

 

[Calvin Speers]

HI I have a 2520, bought this summer. It does the same thing. The motor is the same in both.

 

[Muxster]

Thanks guys... its comforting knowing it starts so easily when cold. Wasn't sure the brief auto fast idle feature was normal but I guess it is. It must be done mechanically some how because I don't think the 790 has an electronic brain. Also a friend has a 3520 and it doesn't auto fast idle when cold.