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I have a TORO (see year and model details in my profile) that started "surging / hunting" last fall and naturally it's still doing it this spring (= engine runs fast, slow. fast, slow etc. all on its own when simply sitting and idling). The machine is about 5 years old and it starts and runs fine, but I just don't like the current "surging / hunting" behaviour when it's idling.

I cleaned its air filter [the thin foam piece + it's paper filter part] but it's behaviour hasn't really changed. (Note: The air filter parts were very dirty, so I thought cleaning it might solve the problem but it hasn't). I'm also using fresh gas.

Any suggestions on what I should try next? Is there an option to try, before actually starting to work on the guts of the carb? Does the carb have any adjustment screws?

Surging is always caused by a weak air:fuel ratio.
This can be due to a lack of fuel ( blockage ) or excess air ( leak at manifold ).
Actually cleaning / replacing the air filter usually makes surging worse.

You can start at either the carb or the fuel tank and check for obstructions.
Starting with cleaning the carb is the easiest.
You will find cleaning instructions here http://outdoorpowerinfo.com

If your mower has a closed loop tank breather they can get clogged enough to reduce the fuel flow enough to cause surging.

If you have a Loncin (also know as a Toro engineered engine) I have a trick you might try where you don’t have to disassemble the carb. Tip the handle down to the floor and put a jack stand under the front end. Look at the front of the engine and behind the air filter you’ll see the carb. You should see a black plastic screw which looks like a throttle speed adjusting screw. It will have a T slotted head or have a D shaped opening. You can remove this screw with a screwdriver and set aside. This screw was holding in the idle jet, which you will see as a black plastic part. With a small screwdriver pry this jet up and loose and take out with a forceps or needle nose pliers. There is a large hole going across this jet and a very small hole up the bottom. This small hole ( about .016 inches in diameter ) is probably plugged and needs to be cleaned and opened up. It should also have a good O ring on it. This O ring only needs to be replaced if it is broke or cracked. This is not easy and unless you have micro drills or very stiff small wire, it’s next to impossible. I use a number 79 micro drill bit and after I have it open I make it a bit larger with a number 78 bit. After I have it open I clean out the opening with carb cleaner. Insert it back in the carb, making sure that one of the flat edges is facing out toward you. Push it down tight with your screwdriver. If you are unsure of this step, take a picture of the jet before you remove it. Now put that adjusting screw back in, you just screw it in so the head holds the jet tight in place, it has no other use.

Thanks for your comments, bertsmobile. The site you pointed me at looks great. I'm sure I'll be able to find my carb there and then decide whether I want to try to attack it now, take it to a shop for service or more likely just wait to work on it myself after the mowing season is over (I wouldn't want to take a chance of having it out of commission for a while if I mess up).

Thanks for the thought, Rivets. Because I have issues with fine motor control of my right hand, I'll skip investigating the possibility you've suggested. (It sounds too much like doing "microsurgery" to me, so it's not an option for me),

Hello;

Reactivating this thread, as I need that small/thin O ring for the idle jet, and have no idea where to get one or even a part number. Can the O ring be gotten by itself, or do you need to buy both the idle jet together? Guys at my local parts shop were too busy to look deeply.

This is on a Toro 20383 SR4, with a Loncin engine Model: 120 3949 Serial: 111100002523

Thanks much.

That O-ring is not sold separately, nor is it part of the carb repair kit.

Rivets said:

That O-ring is not sold separately, nor is it part of the carb repair kit.

Click to expand...

Thanks Rivets for the quick reply! Any suggestions on how/where I can find one? These O rings are so darn thin....

Don’t know where you can buy those O-rings. Best bet would be an old fashion hardware store, might have something around. If you disintegrated that O-ring you better check your gas. The only time I’ve seen that part go bad is when the customer allowed the carb to sit with old fuel in it. Might be time to get a new carb.

Absolutely. I was having the surging issue and pulled the jet, only to find it had about half of the O ring. Then cleaned the carb.

I've got a feeling that I might have issues down the road without an O ring in that location....

Might want to try taking it to you local repair shop and see if they have an old one laying around. If they do pay big time for it, as they are preventing you from purchasing a new carb.

Gsnod said:

Hello;

Reactivating this thread, as I need that small/thin O ring for the idle jet, and have no idea where to get one or even a part number. Can the O ring be gotten by itself, or do you need to buy both the idle jet together? Guys at my local parts shop were too busy to look deeply.

This is on a Toro 20383 SR4, with a Loncin engine Model: 120 3949 Serial: 111100002523

Thanks much.

Click to expand...

hi.
If you measure or get someone to measure the ,grove depth and diameter where the O ring fits I can send you one for the cost of postage.
Hutch.

Just get a new Chinese carb off ebay or amazon. Usually around $12.00 shipped to your door. These carbs are not even worth cleaning anymore when a new one is so cheap. People running ethanol fuel take notice of this.

Also remove and clean the fuel tank. You can rinse the tank out with Diesel then paint it on your wooden stockade fence. Replace the fuel line. Install an inline filter and fuel shutoff (on ever mower). Use fuel stabilizer and fresh NON ETHANOL fuel. Change the oil every two months. It only holds like 18 ounces. Not going to break the bank. Get a 2 gallon jug of Supertech 30w at walmart for $19.75. Will last you a long time.

slomo

When I have a very small port to clean I throw it in a pot of boiling water for a while. It usually works. For the O-Ring, you can buy a cheap kit that has about 50 different sizes, down to really small. Something should work. If your in Canada, Princess Auto has kits and I would imagine Harbour freight in the US would have them.

Search the archives for "jet o ring" some one posted a link a while back to a McMaster & Carr number.
Down side was the packet was something like 20.
Jet + o ring is a purchasable part but not the O ring by itself as the cost of shipping would be 10 times the cost of the rings themselves which is why you have to buy them in 20 packs.