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Need Help WithToro Wheel Horse Carb Issues

Posted by itzbinnice Long Island NY (My Page) on
Mon, Jun 9, 14 at 9:30

My neighbor was given a used older Toro riding mower,14-38 HXL Model 71193, with carb model 497061 from his wife as a gift.
She bought it from her cousin who buys used mowers and sells them. The mower has begun to have fuel issues.
There is something wrong with the float since the engine keeps flooding and the cylinder builds up with fuel and will not crank because of the pressure build up. The fuel also contaminates the oil and must be changed. The cousin that sold the mower had installed a fuel shut off valve and instructed to shut the fuel off when not in use, This worked for a while but now constantly floods when attempting to start.

He has no experience with mower repairs and I am far from an expert.
This engine (14 HP Briggs) has a solenoid that screws into the bottom of the bowl and holds the bowl in place to the carb body. We tried to remove the carb but the 5/16 head bolts (brass) stripped and we were unable to remove the carb. We may replace the carb so when a replacement is found we will use vice grips to remove the bolts and replace them.

I've never seen a carb like this and I'm puzzled regarding the solenoid.
I removed the solenoid and the bowl dropped down revealing the float. The float had little movement which surprised me.
Looking at the carb diagram, the solenoid inlet needle goes into the inlet seat.
When the key is turned on the solenoid engages and pulls the solenoid needle away from the seat.
I assume this would let fuel to flow constantly which makes no sense to me since whenever the key is on the solenoid will behave as described,

Can somebody please advise me the principals of how these solenoid carbs work.
The mower is not in the best of shape so I'm not even sure if it's worth it to replace the carb


Follow-Up Postings:

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RE: Need Help WithToro Wheel Horse Carb Issues

"Looking at the carb diagram, the solenoid inlet needle goes into the inlet seat.
When the key is turned on the solenoid engages and pulls the solenoid needle away from the seat. "

I'm not sure how you came up with that?
The fuel solenoid is simply a plunger that blocks the main jet when power is removed to avoid after fire/run on.

The float needle & seat simply isn't sealing off the fuel flow for whatever reason. Possibly a piece of crud??


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RE: Need Help WithToro Wheel Horse Carb Issues

Bill,
Thanks for the reply, I now undestand it better.
With the key OFF the solenoid plunger is in the extended position that SHOULD seal off the main jet. With key turned ON it retracts and lets the fuel flow.

Although I'm still stumped with the float. By blowing into the fuel inlet valve hose with the float at rest no fuel can enter, by pulling down on the float a bit the blown air will now reach the bowl, however, that distance of float travel is minimal. Without touching the float no air can be blown into the bowl, quite the opposite of what I expected since it's flooding.

I really need to get the carb off to disassemble and clean, but I'm still unsure how to adjust the float since it has such minimal travel distance.

Since the carb hold down bolt heads are stripped, I'll try to put two nuts on the stud, locking them together and attempt to back out the studs that way, but I'm not optimistic about that since the studs are brass and are soft.


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RE: Need Help WithToro Wheel Horse Carb Issues

Floats generally don't go out of adjustment. Metal floats can spring a leak and fill with gas but I've only seen that rarely

Bill is right on point advising you to look for a piece of crud. A very small piece of dirt can result in exactly what you're experiencing.

Also look for a loose jet or nozzle.

Be VERY careful with those carb studs. Snap them and you'll increase the difficulty factor of this repair exponentially.


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RE: Need Help WithToro Wheel Horse Carb Issues

OK, first of all, let me say that fuel does not flow out of a carburetor into the engine because it is pressurized by a fuel pump, or by gravity. There is a form of pressure involve in how fuel gets from the carb to the engine, but not like you may have thought
Lots of folks think that a fuel pump, or gravity pushes fuel out of the carb and into the engine. That ain't how it works with a carburetted fuel system.
A carburetor operates like this:
The carburetor Fuel Bowl is FILLED with fuel by a fuel pump or by gravity, but that is only for FILLING the bowl.
The float then rises as the fuel fills the bowl and as the float rises, it operates a "needle valve" to close off the flow of fuel into the carb so that the flow of fuel INTO the bowl is stopped at a specified point, or "float level".
Fuel is "withdrawn" from the carburetor bowl and into the engine induction system (intake) due to what is called "venturi generated vacuum", which is created when the air flow being inhaled by the engine causes a "vacuum" inside the carburetor throat. Because there is a vacuum inside the carburetor, atmospheric pressure is able to cause the fuel to flow out of the bowl through prescribed passages and into the carb throat.
The strength of the venturi vacuum applied to the carb fuel passages is in direct proportion to how far the carburetor throttle plate is opened. Open the throttle plate, and you are "giving it the gas"......as in: "Here, take this gas, its a gift.".
Not like the carb is force feeding gas to the engine, but only OFFERING the gas to the engine, venturi vacuum is actively drawing the gas out of the carb bowl, not simply receiving the gas fed to it.
That is the basic outline of how carburetion works.
Now, about that strange little solenoid on the bowl.
That solenoid is included in the more recently manufactured engines to prevent what is known as "afterfire combustion" in the exhaust system. Afterfire is most commonly called "back fire" by people who have heard it.
Afterfire happens AFTER the engine has been put into shut down mode (ignition system has been stopped) either by the operator turning off the key, or because a safety interlock switch has been activated (seat switch etc.)
Afterfire is the loud bang that issues from the muffler/exhaust system as the engine finally winds to a halt after the ignition system has been turned off.
Old school machines where there was not a fuel solenoid would almost always produce a loud bang or pop when shut down hot. That is because even though the ignition system has been "killed", the fuel system continues to carry fuel into the still spinning engine by venturi vacuum.
The interior walls of the exhaust system are still hot enough to support combustion at all times during engine operation, but because there is little or no fuel in the exhaust stream, afterfire is not possible when the engine is running.
But..........just as soon as you shut down the ignition system, fuel is no longer burned INSIDE the engine. Instead, the unburned fuel flows on into the exhaust system, where temperatures are still high enough to ignite the fuel.
So long as the exhaust stream is rushing through the muffler while the engine winds down, the fuel does not ignite.
But when the engine finally stops, the fuel heats up and detonates, and that is when the bang occurs.

The fuel solenoid prevents (or minimizes) afterfire by stopping the flow of fuel out of the carb main jet as soon as the key switch is turned off.
With the main jet now closed off by the solenoid valve, the fuel component is mostly absent from the air flowing into and out of the engine. This "air only" flow through the engine effectively purges all traces of residual fuel from the exhaust system, so there is no fuel to make the big bang.

Now, back to your neighbor's carb.
Installing a manual fuel shut off valve does work to prevent any small leakage past the needle valve from drowing an engine while the machine is stored between use cycles.
But, the fact you see little movement in the float may be an indication that the float system is not working correctly, and is incapable of shutting off the fuel flow, or " maintaining optimum fuel level" during operation.
During operation, the float keeps the needle valve ALMOST SHUT OFF, allowing only enough fuel into the bowl to maintain the correct fuel level. The fuel rate entering the carb exactly matches the rate at which the engine is withdrawing fuel from the carb........but only if everything about the float, needle valve, and its valve seat.....are in good order.
If the float and needle valve are not operating properly to limit fuel entering the carb, the fuel level will rise and overflow the bowl and when that happens, the fuel mixture becomes too rich to burn efficiently, and the engine might not run at all.
I think in the case of you and your neighbor, a new carb will be the best action to take. And replace those bolts with new also, vise grips are not the tools to use for installing bolts.
Removing when necessary, yes. Installing.......never.


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RE: Need Help WithToro Wheel Horse Carb Issues

The float is plastic so quite unlikely it has a leak.

I agree, removing the studs will be a challenge since they're brass. Will soak with penetrating oil and let it sit before attempting removal. Can't use heat that can potentially start a fire.

Once the carb is out I can get a better idea of what the problem may be. I still don't know if the float can even be adjusted if need be since I don't see any tangs to bend.
There is just a pin that holds it in place.


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RE: Need Help WithToro Wheel Horse Carb Issues

@mownie
Thank you for taking the time for a comprehensive explanation on how the carb system works. I now see the reasoning for the solenoid.

I agree, I think it's best to replace the carb and studs to have it function properly. Since the rider is so old and not in the best of condition my neighbor will have to decide if it's worth the cost of the replacement parts.
He checked a local mower parts store and was told the carb alone is 150.00. The mower is not worth investing that much into since the mounting studs will be another 12.00

I checked on Ebay and found a new replacement carb for 90.00 and free shipping. The only problem is the part # is different.

http://www.ebay.com/itm/331223330404?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT#ht_2894wt_1242

The parts for his 28N707-0131-01 indicates Carb part # 497061.

The replacement part on Ebay indicates replaces Carb Part # 498061.

Looking at both parts schematics I see all the component carb parts are the same, the only difference is the carb part #. I think it would fit and that the 498061 is newer than the 497061. I can't find a 497061 replacement doing a google search.

I'm going to call the seller and see if he knows if the 498061 will work.

Many thanks to all that responded, I sincerely appreciate your input.


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RE: Need Help WithToro Wheel Horse Carb Issues

Instead of penetrating oil get a can of PB Blaster which is sold almost everywhere. Judicious application over a few days works amazingly well especially on non like metals.

You have to get the carb off to repair or replace so that's first.

If you don't have the knowledge to see what the problem is with the carb I'd get the carb to someone who does before I spent the $$$ for a new one. Physical damage aside I've never had to replace a carb that I could get parts for and that's a lot less expensive than a new one... and that's IF you can get the correct replacement carb.

This post was edited by justalurker on Mon, Jun 9, 14 at 19:28


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RE: Need Help WithToro Wheel Horse Carb Issues

Follow Up,
I got the studs off by using PB Blaster and vice grips, came out quite easily. I then used a file and squared off the rounded bolts to fit a wrench. Next I used a die to thread the bolts the vice grips had damaged. Keeping these only as spares since we bought brand new ones as a replacement.

Next I ordered a new carb on Ebay (big mistake).
While waiting for the car to arrive I took the original carb apart, cleaned everything and used my compressor to blow out all the orifices. I replaced the carb bowl rubber gasket with one from my spare parts.

When the new one arrived I installed it, I then opened the fuel shut off valve. Gas started pouring out of the top of the bowl and flooded the engine. While it was leaking I tried to tighten the solenoid to put more pressure on the bowl gasket but it did no good. Removed the carb, then the spark plug, and cranked the engine until all gas was discharged. Also changed the oil just in case it got contaminated with fuel.

Next I installed the old one (original) I rebuilt.
No fuel leaks, started right up and runs smoothly.
I returned the new one purchased on Ebay and got a full refund less return shipping. I couldn't believe a brand new carb would also have float issues. I tested it before installing by blowing through the fuel inlet while in the mounted position. I was able to blow air into the bowl (worked properly. I then turned the carb upside down and blew in again, no air entered since the float was in the closed position (worked properly).

I have no idea why the thing overflowed like that and at this juncture no longer care.


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RE: Need Help WithToro Wheel Horse Carb Issues

Yeah, some folks can fall off a 12 foot high wall onto concrete--and never get hurt!
Consider yerself lucky! And, lucky because yer fix worked! by: That old sage--rusty Jones


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