Help me understand...

[atpchas]

I have a Stihl BG86 blower. It starts on the first pull almost every time. On a cold start, it sounds like it is running very rich and does not develop full revs/power. After about a minute, it abruptly cleans up and reaches full power/revs. The transition is almost instantaneous, not gradual. I'd like to know what is happening to cause this sudden change. I would think that changes due to engine temp increasing would be more gradual whereas this transition occurs in a second or two. Or maybe the engine temp gets to the point where the incoming fuel suddenly vaporizes more quickly/completely? In any event, I'm completely satisfied with the blower's performance, I would just like to understand what's causing the sudden (and welcome) change.

 

[HarleyT]

On the cold start time frame, play with the choke and see if it runs better on partial choke, to see if it is indeed rich.

 

[atpchas]

On the cold start time frame, play with the choke and see if it runs better on partial choke, to see if it is indeed rich.

Adding choke drops the revs.

 

[Lawless]

My BG55 does the same. Once warm it cleans up and revs. I have it tuned just barely past 4 stroking when hot so when cold it is pretty rich.

 

[atpchas]

My BG55 does the same. Once warm it cleans up and revs. I have it tuned just barely past 4 stroking when hot so when cold it is pretty rich.

Mine is similarly tuned. Until I figured out that the blower would run so differently after a minute, I was getting frustrated retuning it every time I used it.
What I'd love to know is what is causing the sudden transition. A gradual change would make more sense to me.