# Best to run carb dry when putting away at night or no?



## Snowslinger (Feb 1, 2019)

Assuming that I am using ethanolated fuel with a stabilizer would it be better to shut the fuel supply off at the supply valve and run it dry until it shuts off or kill the ignition and just leave some in the bowl?

I’m not talking about seasonal storage just in between uses during the season.


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## WVguy (Nov 24, 2018)

You'll get different opinions. After every use I turn off the fuel and let it run until it dies from fuel starvation. Others leave fuel in the carburetor bowl and have had no ill effects. At end of season I even remove the carburetor bowl drain screw and drain out that last little bit.


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## cranman (Jan 23, 2016)

no......


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## Dannoman (Jan 16, 2018)

I turn off the fuel and let it run dry. Not sure if that's the absolute best thing to do but I figure if no gas is in the bowl there is less of a risk of water and gum building up in the carb.


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## Snowslinger (Feb 1, 2019)

WVguy said:


> You'll get different opinions. After every use I turn off the fuel and let it run until it dies from fuel starvation. Others leave fuel in the carburetor bowl and have had no ill effects. At end of season I even remove the carburetor bowl drain screw and drain out that last little bit.


Okay thanks. Hey since you do the same thing, have you ever had any leakage from around the carb when priming it before starting? I’ve never had it before but did the other day and wasn’t sure if it was definitely from a leak or if it just overflowed out of something from over-priming?


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## WVguy (Nov 24, 2018)

I've never had it leak fuel from use of the primer but I've seen youtube videos in which that does seem to happen a lot. As long as it doesn't leak when using or when the engine is off I wouldn't worry about it.


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## Dannoman (Jan 16, 2018)

On my old MTD I have the same leakage when I prime. It's not unusual and nothing to worry about.


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## Town (Jan 31, 2015)

I don't think the fuel shut-off valve is designed for frequent operation so I leave it open, relying on the carb float valve to shut off fuel flow to the bowl. The float bowl valve is designed for frequent operation. Never had any problems. Allowing the engine to run out of gas and buck and spit as it does so every use is not a great idea in my opinion.


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## sscotsman (Dec 8, 2010)

My thoughts from another recent thread:

IMO, there is absolutely no need to run the carb dry after every use. 
Does it hurt? Probably not.
Does it help? Probably not.
Is it necessary? Definately not. 

It could actually be worse though, because you are getting *most* of the gas out of the carb, but not all, so the little bit left over could dry out leaving varnish deposits behind, which could then gunk up and clog the carb. But if you just leave the gas alone until the next use, days or weeks later, there is too much gas to dry out completely, which IMO is the far better scenerio.

Most people do drain the carb, but *once a year*, at the end of winter, to prep the machine for 7 or 8 months of summer storage. In that case, they also remove the carb bowl and dump the excess gas, and wipe down the carb, to be sure its fully dry. Recent thread on that topic here:

https://www.snowblowerforum.com/for...scussion/146667-end-season-run-dry-treat.html

If you choose to run it dry after *every* use, its probably fine. But IMO there is no good reason to do it, and it could in theory be worse than not doing it.

Its always best to follow the manufacturer recommendations:



> In the Honda 1332 Manual it states:
> 
> To shutoff track unit:
> 
> ...


Which in this case is *not* running the carb dry after every use.

Scot

Copied and pasted from thIs thread 

https://www.snowblowerforum.com/for...35-shutting-off-storing-honda-snowblower.html


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## 59ctd (Jan 25, 2014)

In between uses I just shut the machine down. No need to run the fuel out of the bowl for such a short period - IMO.


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## RedOctobyr (Mar 2, 2014)

I've done it both ways, with no noticeable difference. Currently, I've been running it dry after using, but that's partly because I have no idea when it will actually be needed again. 

A middle ground would be to just close the fuel shutoff between uses. That helps avoid drips, or a crankcase full of gas (bad news), if the float valve starts leaking.


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## Snowslinger (Feb 1, 2019)

Town said:


> I don't think the fuel shut-off valve is designed for frequent operation so I leave it open, relying on the carb float valve to shut off fuel flow to the bowl. The float bowl valve is designed for frequent operation. Never had any problems. Allowing the engine to run out of gas and buck and spit as it does so every use is not a great idea in my opinion.




The bucking and spitting is exactly what conceded me a bit. I’m sure it’s fine but on a regular basis could it cause problems or cause unnecessary wear? Who knows


Sent from my iPhone using Tapatalk


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## Snowslinger (Feb 1, 2019)

Thanks scotsman! 

The little things like the fact that if you leave only a little in the carb then it’s more likely to varnish is exactly what I was looking for.

I’ll leave the bowl full till the season ends!


Sent from my iPhone using Tapatalk


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## tlshawks (Feb 9, 2018)

I do simply because I own too many snowblowers (wide smiley face), and while I try to use them all every time I have snow to throw, our winter storms can be infrequent enough to where sometimes, the latest time I use them is the last time that winter I use them.

I've had winters where they don't get used past New Years Day. Last winter (especially late January to mid April) - and so far this winter (especially the last 3 weeks) - lots of use compared to our average winters.

I never used to run them dry and I constantly fought carb issues - and that's with using 91 no ethanol pump gas. I started doing it last winter after rebuilds - no issues on those two machines (one sold) since. The other two machines just got rebuilt...doing it with them also.

As the saying goes, "your mileage may vary". But over time, I've become anal with all my gas powered small engine machines - and my "luck" with them has improved across the board. Go figure.


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## Homesteader (Jan 12, 2019)

Snowslinger said:


> WVguy said:
> 
> 
> > You'll get different opinions. After every use I turn off the fuel and let it run until it dies from fuel starvation. Others leave fuel in the carburetor bowl and have had no ill effects. At end of season I even remove the carburetor bowl drain screw and drain out that last little bit.
> ...


The primer pulls a vacuum on the gas line to fill the bowl. Once the bowl is full, excess gas will flow past the jet and come out of the carb’s air intake.

This is a normal process.

Generally three primes is recommended if you follow the manufacturer shut down procedure:
- disengage auger
- throttle from fast to slow
- turn off engine 
- turn off fuel shut off
This leaves the bowl rather full with fuel.

If you run it dry or drain the bowl, then you will need to prime it until you see fuel from the carbs air intake dripping out, maybe 10 pumps or more.


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## RedOctobyr (Mar 2, 2014)

I'm not quite following. Are you saying the printer is needed to refill the empty bowl, after opening the shutoff?

I don't think that's true. Gravity should refill the bowl once the shutoff is opened.


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## Homesteader (Jan 12, 2019)

RedOctobyr said:


> I'm not quite following. Are you saying the printer is needed to refill the empty bowl, after opening the shutoff?
> 
> I don't think that's true. Gravity should refill the bowl once the shutoff is opened.


Gravity will feed fuel to the bowl because the float needle is lowered when carb is empty.
I disengage the fuel shut off, then start priming when the bowl is empty. I don’t wait for the bowl to fill then prime. It’s a guess as to how long it will take, I just start priming until a drip of fuel exits the air intake.
That way I know it’s ready to start.


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## SnowH8ter (Oct 8, 2018)

sscotsman said:


> Most people do drain the carb, but *once a year*, at the end of winter, to prep the machine for 7 or 8 months of summer storage.



That must so nice. At best we get two, maybe three months of lousy dog sledding. July is the only month I'm aware of that has no snow in the record books. :frown:


Re the Op's query, I do turn the fuel off and let the beast pop and fart until she's still. Did that with the old Mastercraft too. However, and as has been noted, the primer may need a workout to get things going again.


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## HCBPH (Mar 8, 2011)

Homesteader said:


> The primer pulls a vacuum on the gas line to fill the bowl. Once the bowl is full, excess gas will flow past the jet and come out of the carb’s air intake.



I think you meant it pressurizes the fuel bowl (at least on a Tecumseh engine). The primer bulb is nothing more than a miniature bellows. Pushing the primer bulb increases the pressure in the fuel bowl which in turn causes some fuel to be forced into the throat of the carb. You'll notice the nipple on the carb where the primer bulb connects is nothing more than a open channel to the fuel bowl area of the carb.

On the question of shutting off the fuel line prior to shut down letting the engine die due to lack of fuel, I do that. One additional thing I've done, some of the older Tecumseh carbs have a drain button on the bowl. If the seal is still good, swapping out the bowl allows you to finish draining the carb bowl when not in use (assuming you've turned off the gas line). I like a dry carb when not in use, but that's a personal thing.


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## Homesteader (Jan 12, 2019)

HCBPH said:


> I think you meant it pressurizes the fuel bowl (at least on a Tecumseh engine). The primer bulb is nothing more than a miniature bellows. Pushing the primer bulb increases the pressure in the fuel bowl which in turn causes some fuel to be forced into the throat of the carb. You'll notice the nipple on the carb where the primer bulb connects is nothing more than a open channel to the fuel bowl area of the carb.


No, I mean’t draw a vacuum. 

https://www.jackssmallengines.com/diy/how-primer-bulbs-work/


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## RedOctobyr (Mar 2, 2014)

Primer bulbs for small 2-strokes with diaphragm carbs work differently than larger engines with float carbs. On float carbs, at least the ones I've worked on, the primer does pressurize the line going to the bowl. 

As HCBPH said, you're compressing a flexible bellows, pressurizing the air in it. Then when you let go, your finger uncovers the hole in the middle of the primer button, allowing air back in, as the bellows expands again. 

And even on my weedwhacker, etc, I think the primer may also be pressurizing the tank. There can be some resistance while pushing it, so it's doing something during that phase. I think it may pressurize while pushing it, then draw a vacuum while the bulb expands back to its normal shape.


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## sturgissteele (Feb 7, 2019)

I wonder if, on a 2-stroke, pressing the bulb pushes fuel in and on the rebound, it pulls fuel up into the bulb which allows you to repeat the process. 

On the 4-stroke, the bulb has a hole in it. Covering the hole with a finger while depressing pushes fuel in but can't make any vacuum when rebounding because of the hole now opened.

I'm not an expert, by any means; but I did stay at a Holiday Inn Express once. 

Sent from my moto x4 using Tapatalk


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## HCBPH (Mar 8, 2011)

Homesteader said:


> No, I mean’t draw a vacuum.
> 
> https://www.jackssmallengines.com/diy/how-primer-bulbs-work/


Notice I said Tecumseh engines (should have said 4 cycle but didn't - sorry), which that does not appear to be for. I've even blown into the hose to 'prime' an engine before. See this query for pictures:
https://www.google.com/search?sourc.......1..gws-wiz.....0..35i39j0i131.mxo0ueZSf1A

There's only a single hose on a Tecumseh primer which pressurizes the carb bowl. Never saw one like that before, what's it off of?


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## RedOctobyr (Mar 2, 2014)

sturgissteele said:


> I wonder if, on a 2-stroke, pressing the bulb pushes fuel in and on the rebound, it pulls fuel up into the bulb which allows you to repeat the process.


That's what it seems like to me. Once the primer gets things moving, I think my little diaphragm 2-strokes flow on both the press, and the release.


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## RedOctobyr (Mar 2, 2014)

HCBPH said:


> There's only a single hose on a Tecumseh primer which pressurizes the carb bowl. Never saw one like that before, what's it off of?


His primer bulb picture looks like the one on my 2-stroke weedwhacker (or similar equipment) with a diaphragm carb.


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## HCBPH (Mar 8, 2011)

Now a diaphragm carb makes sense for a 2 line bulb. No bowl to pressurize so suctioning fuel in would be the most logical solution I assume. Haven't worked on one of those so never seen one.


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## SimplicitySolid22 (Nov 18, 2018)

HCBPH said:


> Now a diaphragm carb makes sense for a 2 line bulb. No bowl to pressurize so suctioning fuel in would be the most logical solution I assume. Haven't worked on one of those so never seen one.



HCBPH how the heck is it going??? Do you still have those killer Craftsman II's I think it was???


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## gibbs296 (Jun 22, 2014)

The main reason I shut off the fuel and run my machines dry is to prevent fuel smell from any leakage. I love my snowblowers, but they all seem to weep fuel a bit sometimes and if I run them dry, no smell of gas.


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## ron3033 (Oct 22, 2015)

HI Snow slinger
I have a 42 year old ariens ST 724 
The instructions say to leave it dry. The only carb part I ever changed was the little "O" ring that the adjustment screw in the fuel bowl seals.
In the spring I run it. Take off the gas tank and put the gas in the lawn mower. Swish the tank out with seafoam or carb cleaner and dump out. Start blower and let it run and stall, restart as needed, I spray carb cleaner down the fuel line and restart the blower. I spray carb cleaner in the carb, when it will not run I take the float bowl off and spray it and the float and wipe out the bowl. Clean the needle adjustment. Put it all back together, set at 1 1/8 turn. Change engine oil, put a capful of oil down spark plug hole and turn over. Then grease and give a coat of wax. Put her away. It will start generally on first pull in the late fall with fresh gas, if not the second pull. When warmed up I readjust the needle setting under load by ear, a very, very slight tweak rich. There is only a choke on the engine, no primer.
I have fixed blowers for friends, usually the main culprit is gummed up carb, dirt and water in the carb and especially the carb bowl. They had left gas in them over the summer.
If you are able to get marine gas it has no ethanol, some premium gas does not as well. A little Seafoam in your gas container is a good idea, as frost will often form inside your gas can and lead to water in the gas.
Any way that is my 2 cents, but it works, my Ariens always goes. Hope this helps.
ron3033


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## Homesteader (Jan 12, 2019)

HCBPH said:


> Homesteader said:
> 
> 
> > No, I mean’t draw a vacuum.
> ...


Notice I said pulling a vacuum on the fuel line. 

Just because the primer is pushing air, does not mean it isn’t pulling a vacuum.

It’s no different than using compressed air to pull a vacuum and start a siphon.

<iframe width="560" height="315" src="https://www.youtube.com/embed/PuS3QkH7Wn4?start=45" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen>


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## UNDERTAKER (Dec 30, 2013)

Snowslinger said:


> The bucking and spitting is exactly what conceded me a bit. I’m sure it’s fine but on a regular basis could it cause problems or cause unnecessary wear? Who knows
> 
> 
> Sent from my iPhone using Tapatalk


* I have been running everything Bone Stinking dry after every use. that being Lawnmower, SnowBlower, Generator and in all my years here on this 3rd Rock from the Sun I HAVE NEVER, EVER HAD 1 BLOODY PROBLEM DOING IT THIS WAY!!!!!!!!!!! k:k:k:k:k:k:k: *


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## HCBPH (Mar 8, 2011)

SimplicitySolid22 said:


> HCBPH how the heck is it going??? Do you still have those killer Craftsman II's I think it was???


Still hanging in there. Retiring (so to speak) soon. I'm officially retired from work about 4 months ago due to conditions beyond my control. Down to 4 or 5 blowers for the moment. The Searsasaurus is still my go-to machine for snow. It starts and runs when the Ariens wouldn't. Planning on making a Searsasaurus clone this spring, I've already collected all the parts so it's just a matter of time and warm weather to put it together.

Oh yeah, the Searsasaurus isn't a Craftsman II, it's build from the earlier gear drive model machines. Got to love it.


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## SimplicitySolid22 (Nov 18, 2018)

Nice!!!!!! Cant wait to see your Searasaurus clone. Glad Searasaurus I is still treating you well!!!!!! 



Well I hope you are hanging in there due to beyond your control. I can't believe you only have 4 or 5????? HAHAHA.....Geesh I only have one...well one and a half my little Toro power curve for Deck. Thinking about a Second one for spring myself either a Gilson or a Bolens??? I have a thing for the mid 90's Bolens look...No Idea why. Green with light green lettering. Want to repower one.


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## tadawson (Jan 3, 2018)

Homesteader said:


> No, I mean’t draw a vacuum.
> 
> https://www.jackssmallengines.com/diy/how-primer-bulbs-work/


That's on a 2 cycle, not a 4 cycle blower engine. As stated prior (and I have personally verified on Tecumsehs), the primer bulb stays dry and pressurizes the bowl. On a 2 cycle, the bulbs are wet and draw in fuel and force it into the carb via a totally different mechanism.


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## RedOctobyr (Mar 2, 2014)

Homesteader said:


> Notice I said pulling a vacuum on the fuel line.
> 
> Just because the primer is pushing air, does not mean it isn’t pulling a vacuum.
> 
> ...


From Tecumseh's 4-stroke OHV engines Technician's Handbook, page 9: 



> Primers may be mounted remotely or as an integral part of the carburetor. The basic function of the primer is to supply an air pressure charge to the carburetor main well or carburetor bowl to displace fuel directly into the carburetor venturi. This displaced fuel provides a rich mixture necessary for engines to start easily on the first or second attempt (diag. 4 & 5).
> 
> Primers must be vented either internally through a passage in the carburetor air horn prior to the venturi or externally through a hole in the primer bulb. The vent allows atmospheric air to enter the fuel bowl during operation and to fill the primer bulb after the primer bulb is released.


You push the primer button. It pressurizes air into the bowl, which forces fuel from the bottom of the bowl, up the main jet, into the carb's throat. The jet is the outlet available from the pressurized bowl, as the needle valve is closed. The fuel is coming from the bowl, not getting drawn in from the fuel line. 

Unlike the linked video, I can't see how there'd be any appreciable venturi effect created. There is very little airflow created by the primer bulb, and it has no reason to pass by the needle valve, which is where you'd need to create your vacuum to draw gas in from the fuel line. 

With that said, your video's tip is pretty cool. I've never tried to start a siphon that way, but it's a good thing to keep in mind.


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## Homesteader (Jan 12, 2019)

RedOctobyr said:


> Homesteader said:
> 
> 
> > Notice I said pulling a vacuum on the fuel line.
> ...


It’s still pulling a vacuum. 

The excerpt from the manual quotes the “venturi” a form of vacuum pump - a part of the carb responsible for creating the Venturi effect or vacuum pump, hence “pulling a vacuum”

The Venturi Siphon is exactly what I showed you in the video with compressed air and the same physics are at work in the carb with the fuel line and primer.

Venturi Siphon: A venturi siphon, also known as an eductor, is not a siphon but a form of vacuum pump using the Venturi effect of fast flowing fluids (e.g. air), to produce low pressures to suction other fluids; a common example is the carburetor. See pressure head. The low pressure at the throat of the venturi is called a siphon when a second fluid is introduced, or an aspirator when the fluid is air, this is an example of the misconception that air pressure is the operating force for siphons.

From wiki
https://en.m.wikipedia.org/wiki/Siphon#Venturi_siphon


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## RedOctobyr (Mar 2, 2014)

Homesteader said:


> It’s still pulling a vacuum.
> 
> The excerpt from the manual quotes the “venturi” a form of vacuum pump - a part of the carb responsible for creating the Venturi effect or vacuum pump, hence “pulling a vacuum”
> 
> The Venturi Siphon is exactly what I showed you in the video with compressed air and the same physics are at work in the carb with the fuel line and primer.


I get how the venturi siphon works, and it is pretty cool. 

But they are referring to a physical item, when talking about the carburetor venturi. Not referring to a venturi effect, creating negative pressure (vacuum), etc. They may as well be saying "to displace fuel directly into the carburetor *nozzle*". They're not saying it to mean "to displace fuel directly into the carburetor *vacuum*". 

The carb's venturi is only creating negative pressure when a lot of air is rushing in through the carb's throat, towards the engine, due to being drawn in by the piston moving down during the intake cycle. When the air is just sitting there (not running), no vacuum is being created by the venturi. 

https://en.wikipedia.org/wiki/Venturi_effect
https://carbiketech.com/carburettor-venturi-design-theory/

I apologize to all for :icon-deadhorse:


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## Homesteader (Jan 12, 2019)

RedOctobyr said:


> Homesteader said:
> 
> 
> > It’s still pulling a vacuum.
> ...


The shape of the Venturi causes a pressure differential that creates vacuum. 

I said it the beginning just because it’s applying pressure doesn’t mean it isn’t pulling a vacuum.

Pressure pushes. 

Vacuums pull. 

It’s a common misconception to believe pressure is responsible for the uptake of liquids with a gas(air/fuel) but it’s the venturi’s pressure differential (vacuum) that pulls both air and fuel up together. 

The venturi system creates a pressure differential that forms a vacuum. As air flows through the tapered venturi orifice, a rapid change in velocity occurs. This velocity change creates a reduced pressure (vacuum), which draws air and liquid to be injected into the system. The air and liquid injection rates vary with the pressure differential across the venturi.

Their’s a reason it’s called a Venturi and where the air and fuel flow through from bowl to intake when the primer is pressed. 
Think about it.

Try reading a physics book or two before you dismiss an argument and think you’ve correctly educated someone on a topic then leave a condisending remark.
Maybe you’ll learn something - probablly not - I’m certainly done trying.


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## classiccat (Mar 1, 2014)

Homesteader said:


> The shape of the Venturi causes a pressure differential that creates vacuum.
> 
> I said it the beginning just because it’s applying pressure doesn’t mean it isn’t pulling a vacuum.
> 
> ...


You're describing the Bernoulli effect. 

The pressure differential is across the emulsion tube, not the fuel line.

in small engines, the float bowl and fuel tank are both at atmosphere; no pressure differential.


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## tdipaul (Jul 11, 2015)

_"Best to run carb dry when putting away at night or no?"_

mower: no, because it is going to be used every 5-7 days during the growing season

blower: yes, because (in NJ) it could be weeks or months before the next snow, or no more at all.


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## Jason B (Jan 28, 2015)

RedOctobyr said:


> From Tecumseh's 4-stroke OHV engines Technician's Handbook, page 9:
> 
> You push the primer button. It pressurizes air into the bowl, which forces fuel from the bottom of the bowl, up the main jet, into the carb's throat. The jet is the outlet available from the pressurized bowl, as the needle valve is closed. The fuel is coming from the bowl, not getting drawn in from the fuel line.
> 
> ...


Pretty cool diagram you posted.


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