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  #1  
Old 08/25/11, 10:47 PM
 
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learning about choking a gas engine

I have so much to learn to handle things on my own. If I understood these gas engines like my John Deer, gas trimmer, chainsaw, generator it would help me alot. I am learning about the fuel mixtures needed.

I thought the choke was something I would turn on until it starts, but a friend told me today it needs to be off and then slowly open after it starts..???


One thing I have surely learned is that guys never say if they don't know. I have been told lots of wrong & different things about some issues..The one that tells me one day they have no idea about something will have my respect.

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  #2  
Old 08/25/11, 11:16 PM
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Here is what I know, and I am not a mechanic.

The choke reduces the amount of air that goes into the carburator.
With less air, there is more fuel. When you are starting a 'cold' engine you need more fuel and less air, for it to get going and warmed up.
Then, as the engine warms up, you can let off the choke and it will continue to run.

My experience has been that if you let off the choke too soon, the engine may sputter and die, or it may just cough and still run.
I usually do it gradually, while I LISTEN to the engine.
It will generally run really fast and then when you let off the choke, it slows down some. You dont want it to cough or sputter, just run smooth.
If it gets choppy sounding, the engine is not warm enough yet.

It takes practice to get a feel for when to let up on the choke. It takes a lot longer in cold weather.

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  #3  
Old 08/25/11, 11:20 PM
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When starting a cold engine, engage the choke to reduce the air going through the carb. Unless it is brutally cold, you can generally disengage it right away to warm up the engine.

FWIW We bought an Ariens Tiller and they recommend pulling the starter cord handle slowly and returning the handle to its original position when resistance is felt. This is to prevent moist air from intruding into the combustion chamber.

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Old 08/25/11, 11:39 PM
 
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Thanks...

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  #5  
Old 08/25/11, 11:40 PM
 
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On one of our old 1960's pickups, I have to choke it when starting on most days unless it's really hot outside. Engage the choke, let it run for a minute, then ease it off. Same thing with our tiller.

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  #6  
Old 08/25/11, 11:53 PM
 
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Quote:
Originally Posted by Rick View Post
FWIW We bought an Ariens Tiller and they recommend pulling the starter cord handle slowly and returning the handle to its original position when resistance is felt. This is to prevent moist air from intruding into the combustion chamber.
Wha?


All you are doing is pulling the engine over to the compression stroke by doing that.

Makes it a little easier to start if you have a well tuned engine.

Once that sucker fires off, you are pulling in whatever ambient air you got. Moisture or not.

In the summer, you might be able to get by with a half choke position instead of a full choke. It might be that you have to feather the choke as well as it starts up being ready to flip it off entirely.
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  #7  
Old 08/26/11, 12:33 AM
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MAybe the misunderstanding is the term on and off. Open and closed might be better

When the choke is open all the air flows normal as when needed when warm.
When the choke is closed less air flows and the gas mixture is now "rich" [with gas] as needed when cold.

There should be little diagrams on the choke handle or near it that look like open and closed like this

||| Open

|\| Closed

|-| This cold be closed also


L

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  #8  
Old 08/26/11, 12:43 AM
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Each gas engine has it's own little quirkes to get it started. You have to learn those quirkes. Generally, for a cold engine, you turn on the gas (if it has a shut off valve), close the choke completly, pump the primer 4 or 5 times (if it has one), and pull the starter until it starts. As it warms up you can slowly open the choke. Listen to the engine and if it starts to run rough while you are opening the choke, close it a bit and wait for it to warm up some more. When it is completly warm you should be able to open the choke all the way. For a warm engine you can leave the choke open and just pull the starter.

My lawn mower has no choke. You pump the primer about 12 times and it starts on the 3'd pull. My chain saw has no primer. You close the choke, pull the starter cord about 15 times until it sputters, open the choke and it starts on the next pull. On the snowblower you close the choke, pump the primer 3 times, and it starts on the third pull. The weed eater is about the same as the snowblower. So you see each of my pieces of equipment has it's own little sequence you have to go through to get it started.

When you store the motor for the off season, put Stabil in the last tank of gas and run the engine long enough to get the Stabil laced gas into the carburator. This will keep the gas from coating the inside of the carb with varnish. If a few years worth of varnish build up in the carb it will block passages and cause a sticking valve in the carb and it won't run. Most "broken" small engines just need their carbs cleaned. There are guys who make their living fixing small engine type tools and selling them on CL.

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  #9  
Old 08/26/11, 03:08 AM
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And just to add further complexity, there are those engines that have both the plastic pimple primer (PPP) and a partially disabled choke, where choke plate has a significant hole drilled in it.

My solution on those is to use epoxy putty and block the drilled hole in the choke plate, then use the choke like one would a traditional choke and forget about using the plastic pimple.

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Last edited by HermitJohn; 08/26/11 at 03:10 AM.
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  #10  
Old 08/26/11, 08:44 AM
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Over the years we've had so many engines with manual chokes. the colder it is out, the more they are needed. In all cases, the choke needed to be closed before the engine was turned over. For some, you have to open it rather quickly once the engine starts, and others you had to leave it closed for several minutes.

And some times on really difficult to start days (well below zero) You might have to open the choke up fully, stick the pedal flat to the floor and crack it for several seconds until it tried to pop. Then you closed the choke off and cranked it and soon as it started, you had to be opening up the choke just a bit, and if it roared, you opened it more, and if it sputtered, you closed it. Was real fun doing that with a manual truck - one foot on the brake, one on the clutch, one hand on the key, one had on the manual choke.

I was sure happy with DH put a new 4 barrel carburetor on that truck! Still had a manual choke but it wasn't near as temperamental.

Several of our small engines have fuel shutoff valves, and we shut the fuel and let it about run out of gas (or what is left in the line drips out). So when we go to start, closing the choke helps pull the fuel back into the lines. The two lawn mowers are that way, but both are electric start. I can't get either of my rototillers(pull start) to start without closing the choke, but it needs to be opened almost immediately upon starting or the engine will flood out and die.

At least most of my equipment has open/closed designations, and not on/off so I don't get confused which one is open.

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  #11  
Old 08/26/11, 08:58 AM
 
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To add to all the confusion - it may also depend on how "new" what you are trying to start is - some of these new-fangled engines have an "automatic" choke and you can't get to them without an odd-ball screwdriver and a masters degree in engine repair.........

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  #12  
Old 08/26/11, 10:16 AM
 
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Just follow the manufacturer's guidelines. There's no single check-all when using a broad range of different engines. For an older model car with a manual choke, pushing it in gradually may be appropriate.

On my late model generator, it won't start at all unless the choke is all the way closed, but runs best if I release all the choke a moment after it starts.

You just have to treat each engine as an individual and leave it at that.

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  #13  
Old 08/26/11, 11:06 AM
 
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To further add to the confusion many engines have "enricheners" rather than chokes. You would not know the difference if you didn't know the difference. They are actuated in the same way. The difference is a choke limits the air to richen the mixture while an enrichener leaves the air alone but adds more fuel to the mixture.

General rule of thumb is to only use the choke/enrichener for just as long as it takes to get it to start. Once started back off the choke/enrichener and use the throttle to maintain a high idle until the engine warms enough to idle on it's own. Over use of the choke/enrichener can foul your plugs. Some engines are more forgiving than others.

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  #14  
Old 08/26/11, 11:26 AM
 
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Mostly all good advice and it really does depend on the idiosyncrasies of each engine but to the OP, your friend is mostly wrong. Generally you choke a cold engine before you start it and then ease off as it warms.

To give a few examples, our 4 wheeler (250 Suzuki) needs no choke during weather above about 50 but needs full choke below that and it is extremely temperamental about it. On cold days we fully choke it and it starts and after about 3 or 4 minutes we can ease off the choke and its good to go. When its below zero it doesnt like to start at all.

Our garden tractor (26 HP Kawasaki) needs a little choke to start regardless of the weather and then once its started you can ease the choke off almost immediately

The Mrs old Sear garden mule (10 hp Tecumseh) never needs choke.

Our weedeaters, push lawn mowers, the log splitter, trash pump etc have the pimple primer and I never have trouble starting them regardless of the temp,

Our 1948 Allis Chalmers WC Tractor has to have full choke to start regardless of temp and it takes 4 or 5 minutes to warm up before you can ease off the choke

All of our chainsaws need to be choked before they will start regardless of temp but once they are warm they dont need any choke.

So basically, it depends on your temp, the type of engine, and even then you can have two identical engines that react differently (I have a buddy that cant start his 250cc 4 wheeler without full choke) and also you need to back off the choke as soon as you can.

Now your probably really confused!!

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Old 08/26/11, 11:29 AM
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Quote:
Originally Posted by Micheal View Post
To add to all the confusion - it may also depend on how "new" what you are trying to start is - some of these new-fangled engines have an "automatic" choke and you can't get to them without an odd-ball screwdriver and a masters degree in engine repair.........
Your right
My pressure washer has a nothing carb with NO adjustments, A throttle thing of some kind GRRRR and a bulb to pump gas in. I have found the bulb is the choke. I have to push mine till I get some resistance then a couple more times.

I just love govt regulation. If anybosy knows where you can buy an alternate REAL carb let me know or it seems it would be a good start up business.
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  #16  
Old 08/26/11, 12:13 PM
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I hate the plastic pimple primers. I suspect with some tinkering you could make a slide type choke out of sheetmetal simular to whats on many chainsaws to add to the end of a carb without a choke. You probably arent going to make a good butterfly type choke, at least not easily. And unless you can find a carb off an old piece of equipment, you arent going to find any modern carb that has the screw to adjust main jet. The main jet adjustment disappeared first, then the idle adjustment, then the choke itself. And many of the modern carbs just arent meant to be opened and rebuilt, only replaced as a whole unit. And on mowers most modern carbs are intended to run full governed speed all the time without being able to adjust throttle. The horrible thing will be when they figure how to economically put computer controlled fuel injection on your push lawn mower. Mowers are already throwaway, with some complex expensive fuel system they will be even more so.

As to the automatic choke on lawn mower, the Briggs I used to have on my Yazoo had one of those. Talk about annoying plus it used plastic pieces that didnt hold up and werent replaceable separately. With bit of Gorilla glue, bit of baling wire, and piece cut off an old radiator hose, I converted it to a manual choke that worked quite well. Sometimes so called progress is actually regress....

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Old 08/26/11, 12:21 PM
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it would be a good start up business.
It would be illegal to sell alternative unapproved adjustable parts for an EPA approved fuel system. You would have to make it as a replacement part for a pre-EPA designed engine and only sell it for that application. If somebody just happened to adapt it to their existing EPA approved engine on their own initiative, well thats between them and the EPA.... So far we dont have small engine inspections in this country so be unlikely any private individual would get in trouble doing this.
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  #18  
Old 08/26/11, 12:48 PM
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Originally Posted by HermitJohn View Post
It would be illegal to sell alternative unapproved adjustable parts for an EPA approved fuel system. You would have to make it as a replacement part for a pre-EPA designed engine and only sell it for that application. If somebody just happened to adapt it to their existing EPA approved engine on their own initiative, well thats between them and the EPA.... So far we dont have small engine inspections in this country so be unlikely any private individual would get in trouble doing this.
Stuff like that you don't sell. You take donations for your work ANd ya just keep an old piece of junk engine around just in case so you can say you were gonna put it there and just thought yo u would try it. Between what we got now and the old down draft carbs ain't a lot out there.


As far as inspections dont tell that to Gibson guitar, The goat herders and a few others I can reference. And don't forget they soon want to look at your garden.
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  #19  
Old 08/26/11, 01:17 PM
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I hate the plastic pimple primers. .
Wow cause as far as I am concerned that was the BEST thing to happen on small engines in years and years.
Made weed eaters start easier, made chain saws start so much easier, Made Snowblowers start in cold weather very easy.
Can't see what a person would dislike in those primer bulbs. I see none what so ever.
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Old 08/26/11, 02:50 PM
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Many 2 strokes seem to like full choke until the "pop" (give the slightest hint of wanting to start) then 1/2 choke until they start, 30 seconds or so at 1/2-3/4 throttle, until they warm up a little, then take the choke completely off. The only time I have trouble is if I only run one for a minute or so and then turn it off. Seems like they don't like to start back up very well...

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