# Carburetor solenoid



## JOSE M. (Jun 27, 2020)

Hi there, trying to replace carburetor on Kohler Courage 20 (Husqvarna riding lawnmower), solenoid on old carburetor has a red wire, solenoid on new carburetor has a receptacle with 2 prongs, can somebody tell me which one is positive and which one is negative, or it doesn't matter? (carburetor kit comes with male connector with 2 wires -red and black- that fits either way, with red wire on the left, or on the right)


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## marc_hanna (Apr 10, 2017)

It will matter which way, because your red is positive and your black is ground. Usually the plastic plug will only fit in one way. Your old one must have grounded to the block through the metal case.

Inspect the plug and make sure there's not a tab that aligns in the receptacle, it might just be a sloppy fit. It might be energized when the key is on, so you can always try to just plug it in without it being installed and see if the butterfly valve actuates with the throttle. if it doesn't, flip the plug around. Be prepared to replace a fuse.


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## FredM (Nov 18, 2015)

If you own a multimeter, set this to ohms and place a probe on any spade terminal on the solenoid and the other to the solenoid housing and see if you get a reading, change the probe onto the other terminal and do the same as with the other probe to the housing and see if you have a reading, if no reading after touching both spade connectors with the probe, then you have a coil that feeds in positive and the other spade terminal goes to earth.

So you need to connect the red to red and the black to an earth point close by or you could solder a black wire to the solenoid black wire from the connector and run this to an earthing point on the motor, and it wont matter which way the connection fits onto the solenoid if there is no guide to make this connection one way.


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## Bob Driver (Nov 1, 2017)

Not a big fan of anti-backfire solenoids. Just another expensive part that is eventually going to fail..... Idle the engine down for 5 seconds before you shut it off and there is absolutely no need for one.

Kohler Bowl Nut 47 100 06-S runs around $2 wholesale, never fails, and there's only one way to install it. "Righty Tighty, Lefty Loosey" 

I've probably got 20 of them in a tray at my carb bench. When I come across a $20-$50 back-fire solenoid screwing up, it gets a $2 bowl nut and move on down the road


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## andyvh1959 (Jul 1, 2015)

Is the solenoid on the bottom of a B&S Intek single carb also an anti-backfire solenoid? I thought it was simply a fuel cutoff solenoid. Now as I recall, on occasion if I shut the engine off too quickly by turning off the key it would backfire. My natural reaction was to do exactly as you say, throttle it down for 5 seconds before shutdown, no backfire


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## Bob Driver (Nov 1, 2017)

It's sometimes called a backfire solenoid or fuel solenoid, but the technical term
is actually "Anti-after fire Solenoid". 

In my opinion, it is a government mandated, $20-$50, PITA part that routinely fails with the use if ethanol fuel. The tip (rubber, or brass) blocks off the main jet tower when 12VDC is not present. The stem and biasing spring are exposed to ethanol fuel in the off position. Let the engine sit for 60 days and the electromagnet doesn't have enough power to retract the plunger that is coated with shellac from the ethanol fuel breaking down.

Score 1 for the Bright Idea Fairy...


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## Phil B (Jun 11, 2020)

Yeah, the stupid solenoids. Earlier this year, I bought a Sears 2013 lawn tractor that wouldn't start. Seller said the carb needed replacing. I removed the carb and found the solenoid stuck into the port. The mower hadn't been used for a couple months. Worked fine after a cleaning. Made $400 on that mower.


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## Bob Driver (Nov 1, 2017)

If it's a Kohler, I just replace them with a $3 bowl nut


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## andyvh1959 (Jul 1, 2015)

I found the operator's manual for my old 80's vintage Ingersoll/NOMA lawn tractor. In it, is a paragraph that specifically says to avoid a pop/bang on shutdown, slow the engine down to an idle before shutting off the ignition. So it's nothing new, and nothing that requires a complex solenoid system to avoid a "bang" from the exhaust on shut down.


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## Phil B (Jun 11, 2020)

When we bought our Toro ZT in '18, they told us to leave the throttle wide open and shut off the key. I don't think it's ever popped.


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## Bob Driver (Nov 1, 2017)

Personally, I kind of like a pop. It bugs the hell out of the wife. Whenever she gets on my case to mow and I don't feel like it, I can always say......... 

"I don't know if I can. You heard the mower when I shut it off. I think it blew up"


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## andyvh1959 (Jul 1, 2015)

your 2018 Toro ZT doesn't pop because the fuel solenoid is still working. When it quits working, you'll know it, as in hard starting and occasional cylinder flooding. That's what the B&S Intek did over the past two years. It'd be running fine, I'd shut it off to move a branch off the yard, and I couldn't start it again because the cylinder flooded into hydraulic lockup. I'd remove the spark plug, which was wet, and crank the engine over to clear a spray of fuel out of the plug hole. Then it'd start and run just fine again.


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## Phil B (Jun 11, 2020)

I removed the solenoid from the carb, actually by breaking the solenoid off the nut. Of course, the nut is hollow, so I cleaned it all up and filled it with a bit of JB Weld, and it's working great.


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## wjjones (May 28, 2010)

Did you install a inline fuel shutoff valve?


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## Phil B (Jun 11, 2020)

I didn't.


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## Longhorn294 (Oct 13, 2019)

andyvh1959 said:


> your 2018 Toro ZT doesn't pop because the fuel solenoid is still working. When it quits working, you'll know it, as in hard starting and occasional cylinder flooding. That's what the B&S Intek did over the past two years. It'd be running fine, I'd shut it off to move a branch off the yard, and I couldn't start it again because the cylinder flooded into hydraulic lockup. I'd remove the spark plug, which was wet, and crank the engine over to clear a spray of fuel out of the plug hole. Then it'd start and run just fine again.





andyvh1959 said:


> your 2018 Toro ZT doesn't pop because the fuel solenoid is still working. When it quits working, you'll know it, asked in hard starting and occasional cylinder flooding. That's what the B&S Intek did over the past two years. It'd be running fine, I'd shut it off to move a branch off the yard, and I couldn't start it again because the cylinder flooded into hydraulic lockup. I'd remove the spark plug, which was wet, and crank the engine over to clear a spray of fuel out of the plug hole. Then it'd start and run just fine again.


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## Longhorn294 (Oct 13, 2019)

The fuel shutoff solenoid servers one purpose, to stop gas from being sucked into the cylinder (s) as the engine is dying an still spinning and pumping raw gas fumes out your exhaust.. If you're getting gas into your cylinder without it running, your problem is your needle and seat which shuts off the gas when the bowl is full. If your needle and seat are leaking, gas will continue to flow into the bowl, down your intake, into your valves and cylinder ending up in your oil pan. A quick fix is to change your contaminated oil and put a shutoff valve on the fuel line...tho I don't recommend it because the first time you forget to turn it off when you kill the engine, you have a crankcase full of gas again! Best to replace n&s. If the fuel shutoff isn't working, the main Jet is closed off and it won't start at all in the closed position. Usually happens when it's sitting with bad gas and is stuck from varnish. They can be easily cleaned out usually by removing it and sprayed with carb cleaner while working the needle up and down till it frees up...of course, drain and add fresh gas


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## Bob Driver (Nov 1, 2017)

It's actually called an "anti-backfire solenoid" by the OEM's, and you can thank the California Air Resources Board (CARB) for it. California was the first State to establish emissions standards for small engines in 1990.

There are far more small engines in use in the U.S. today than there are cars by a long shot. Some of the emissions stuff can be a PITA, anti-backfire solenoid as an example, but most of it makes sense as far as controlling air pollution. Small engines are 40-80% cleaner today than they were before those programs began in the early90's. I see almost all lawn/garden equipment being battery powered in the next 20 years. It's just a matter of time until they develop the batteries to do the same job as a big V-twin on a lawn mower. When they develop a battery powerful enough for both the ground drive and blades, that weighs in the 100LBS range (same as a V-twin), the path is set. As far as a time line, pay attention to what Briggs and Kohler does, it's their future on the line. They are in the position of being like a major carriage maker, or harness maker, in 1903.... The clock is ticking


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## Phil B (Jun 11, 2020)

We sold the Toro ZT, and will use the Husqvarna Rider 155 to mow the lawn. If she doesn't like that, she can use the X738.


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## Longhorn294 (Oct 13, 2019)

Bob Driver said:


> It's actually called an "anti-backfire solenoid" by the OEM's, and you can thank the California Air Resources Board (CARB) for it. California was the first State to establish emissions standards for small engines in 1990.
> 
> There are far more small engines in use in the U.S. today than there are cars by a long shot. Some of the emissions stuff can be a PITA, anti-backfire solenoid as an example, but most of it makes sense as far as controlling air pollution. Small engines are 40-80% cleaner today than they were before those programs began in the early90's. I see almost all lawn/garden equipment being battery powered in the next 20 years. It's just a matter of time until they develop the batteries to do the same job as a big V-twin on a lawn mower. When they develop a battery powerful enough for both the ground drive and blades, that weighs in the 100LBS range (same as a V-twin), the path is set. As far as a time line, pay attention to what Briggs and Kohler does, it's their future on the line. They are in the position of being like a major carriage maker, or harness maker, in 1903.... The clock is ticking


It's actually called a Fuel Solenoid by the OEMs in their parts breakdown..


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## Bob Driver (Nov 1, 2017)

Longhorn294 said:


> It's actually called a Fuel Solenoid by the OEMs in their parts breakdown..


Huh... I stand corrected. What I actually heard the Instructors call it when I went through both the Kohler and Briggs Service Technician Schools was an “Anti-Afterfire Solenoid” (I made an entry in my notes). That's also what they call it in both sets of study guides they gave out to prep for their certification tests (I just looked it up). I can give you the contact numbers at both schools if you think you need to call that to their attention? 

http://www.small-engines.com/afterfire


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