Basics of Cold Engine Starts, Flooding, Priming, etc.

[WarmGuy]

I had trouble the first time I started my new Stihl, because I had it on the cold start setting for too long, and flooded it. I guess I failed to notice when it first caught a bit, and didn't switch to the warm start position.

Pulling the starter cord with the throttle open (and chain brake on) a few times solved it, and now I've got the hang of things.

But I would like a better understanding of what is happening.

In the cold starting position, is there a choke on, or is there some other way that it makes the gas/air mixture richer?

When it's flooded, is there actually gas sitting in the combustion chamber?

How does opening the throttle take care of the flooding?

My old saw used a priming bulb. Why isn't that necessary on the stihl?

Thanks.

 

[smokinj]

In the cold starting position, is there a choke on, or is there some other way that it makes the gas/air mixture richer? Choke on

When it’s flooded, is there actually gas sitting in the combustion chamber? Yes

How does opening the throttle take care of the flooding? Doesnt always

My old saw used a priming bulb. Why isn’t that necessary on the stihl? Holding the throttle wide open takes care of that

Thanks.

 

[kevin j]

Primers did one or both of two things depending on engine design: 1. pump fuel up through the carb and back to tank to get fuel there before there was any crankcase impulse to operte the fuel pump. e.g. outboard motors. 2. rarely, pump some fuel into the inlet passage in lieau of a choke.

Choke restricts the air flow, thus creating higher vacuum at the carb jetting and drawing up more fuel.

There could be liquid fuel in the combustion chamber, but mainly the vapor to air mixture is simply too rich to burn. gasoline has a fairly narrow rnage in which it will burn (thankfully for safety) compared to say natural gas or hydrogen. There could also be condensed fuel in the crankcacse on a two cycle.

WOT (with choke open of course, or the floodig will get worse) opens the throttle totally, so at cranking speeds the air flow is quite slow, not enough to pick up more fuel into the mix. So the 'mix' going through the engine and out is a lean mixture, thus it tries to evaporate some of the extra gas already in there. Sometimes it clears enough to fire, sometimes the plug is wet and shorting out and it doesn't help. give it a try.

Most small two cycles all start the same, and are very predictable IF the engine is in other wise good tune. Full choke (which usually sets a fast idle also to open the throttle slightly to bring in some mix), switch on, pull until you hear the cough/pop/stumble of some weak firing. It can be VERY quiet, and you can usually feel it better than hear it. At that point, MUST take off choke or it can flood with a couple more pulls. Off choke, pull again, should start. Immediately blip the throttle to get off of fast idle (so the chain or brake are not engaged), let it warm up at idle (to avoid cold seizures) while putting on other gear, then go to work.

Engine hot, no need for choke.

k

 

[Gooserider]

Also it is worth noting that some equipment (i.e. my Dolmar) needs to have things done to the choke, even when doing a hot start.

It is best to read your manual to get the details of the reccomended starting drill.

On my Dolmar, pulling the choke also sets and latches the throttle into a fast idle. When hot starting they want you to pull the choke out and push it back in to set the part throttle lock before pulling the rope...

My starting drill...

Cold
1. Pull out choke,
2. push comp. release button,
3. pull 2-3 times until engine "burps" (comp release will reset if you didn't hear it)
4. push choke in (DON'T touch throttle trigger)
5. push comp. release button (again)
6. Pull to start

Hot
1. Pull out choke, push choke in, don't touch throttle
2. push comp. release button,
3. pull to start

Gooserider

 

[woodconvert]

On my Stihl starting is as follows:

Cold start
1 Put choke full on
2 Two pulls till it barks
3 Choke moved to the next position
4 Pull twice then it's running

Hot start
1 Put choke to full on
2 Forget to push in the compression release
3 Pull once
4 Wait until shoulder relocates and feeling comes back to fingers, remind self to push in compression release
5 Push in compression release
6 Pull once

 

[Gooserider]

I agree... Unless you are doing the full safety-nazi "kneel on the saw" drill (no way do I get my chainsaw boot toe into the rear handle grip...) there is no way you pull the rope on my Dolmar w/o hitting the compression release - it's about like the rope is attached to a solid wall. (And I don't get the fancy "comfort grip" like some of the Stihl saws have....)

Gooserider

 

[jibe]

If that 046 is running right you should just be able to drop the switch from "off" one click to "run" and start it with one pull if it is hot.

If you really flood a saw badly you can always pull the spark plug and let things dry out a little.

When cold, most stihl's seem to "pop" on the third pull with the choke all the way on. Pop it up to high idle and off you go.