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NITRO-BTU · Dec 4, 2007, 09:53 AM

I have a 1997 mtd Yardman 18.5 hp.tractor. I have a no start no run condition which I've tried to trouble shoot. I removed the air cleaner and have been able to run gasoline primes through the air horn so, the ignition system seems to be OK. Secondly, I removed the gas line from the inlet of the fuel pump and have gas to the inlet of pump. I believe the problem has something to do with the carb. However, the fuel pump or possibly something else could be the problem. Please, advise, Thank You, All for your inputs. Sincerely, Jim Norris

KISS · Dec 4, 2007, 10:42 AM

Does it have an elecreical solenoid on the carb? This is the fuel-cut solenoid.

MOWERMAN2468 · Dec 4, 2007, 07:52 PM

??

NITRO-BTU · Dec 6, 2007, 05:51 AM

Originally Posted by KeepItSimpleStupid

Does it have an elecreical solenoid on the carb? This is the fuel-cut solenoid.

NOPE, NO SOLENOID ON THE CARB. THE TRACTOR IS A "YARD MACHINE" NOT A YARDMAN. ANY OTHER SUGGESTIONS? JIM

KISS · Dec 6, 2007, 08:27 AM

Then I guess the fuel valve is stuck in the carb. Time to takei t apart and thouroghly clean the carb and the fuel system. Pay particular attention to the fuel valve.

This assumes that you get a sputter when you introduce gasoline or carb cleaner in the air horn. Don't use starting fluid.

NITRO-BTU · Dec 7, 2007, 05:50 AM

Originally Posted by KeepItSimpleStupid

Then I guess the fuel valve is stuck in the carb. Time to takei t apart and thouroghly clean the carb and the fuel system. Pay particular attention to the fuel valve.

This assumes that you get a sputter when you introduce gasoline or carb cleaner in the air horn. Don't use starting fluid.

Hello there, i get more than a sputter, it runs the engine for a few seconds. Please, define this fuel valve in the carb. Jim

KISS · Dec 7, 2007, 08:14 AM

There are 3 basic carb designs that I know of: 1) float (characterized by a bowl and usually a spring loaded valve to drain the bowl), 2) Diaphram and 3) Direct feed where the carb sits on the gas tank.

Gum and varnish accumulate, especially with fuel left in the engine/tank for a long tiime untreated with additives, like Stabil. I treat fall/winter gas for both 2 cycle leaf blowers and 4 cycle snow blowers. The gas could sit from November to May. Not good.

Well, the gum acts as glue to the fuel valve and varnish restricts passages in the mixture needle valves or makes the fuel valve not seat properly.

In the float type carb, the fuel is gravity or pump fed and stopped by a small valve in the carb. That valve basically lets fuel into the bowl and stops when the bowl is full, because the valve is actuated by a lever arm of a float. If the float gets a hole in it, the carb floods. If the valve sticks, no fuel. Debris in the fuel system may also cause the valve to stay open.

In the diaphram type carb, the valve is very light and small. Gum can easily make it stick.
Engine vacuum basically activates the diaphram and the diaphram is connected to a very small fuel valve. A miniature pump so to speak. If the diaphram gets a hole in it, no fuel.
If the fuel valve sticks. No fuel. If there is debris in the gas, the valve may stay open and the carb floods. The diaphram carb sometimes has a primer bulb attached to it.

Design 3 is not likely in your case.

You already confirmed it's not the gas shut off, fuel filter or fuel pump if equipped.

Some carbs have two mixture screws. One for the idle RPM range and another for high speed.

Both Welcome to the Parts Store and briggsamdstratton.com have engine diagrams on their website.

The only real cure is to rebuild/clean the carb. This requires disassembly.

I'm not sure of the procedure to set the mixture on the newer engines, but in the old ones, you'd just bottom out the mixture screws and open about 2 turns. Start the engine and adjust until it sounds right.

Cars, on the other hand, in later years cars required drilling out the caps on the mixure screws. I set the idle/mixture using propane gas and a tach which would get the emissions right.

NITRO-BTU · Dec 8, 2007, 07:03 AM

Originally Posted by KeepItSimpleStupid

There are 3 basic carb designs that I know of: 1) float (characterized by a bowl and usually a spring loaded valve to drain the bowl), 2) Diaphram and 3) Direct feed where the carb sits on the gas tank.

Gum and varnish accumulate, especially with fuel left in the engine/tank for a long tiime untreated with additives, like Stabil. I treat fall/winter gas for both 2 cycle leaf blowers and 4 cycle snow blowers. The gas could sit from November to May. Not good.

Well, the gum acts as glue to the fuel valve and varnish restricts passages in the mixture needle valves or makes the fuel valve not seat properly.

In the float type carb, the fuel is gravity or pump fed and stopped by a small valve in the carb. That valve basically lets fuel into the bowl and stops when the bowl is full, because the valve is actuated by a lever arm of a float. If the float gets a hole in it, the carb floods. If the valve sticks, no fuel. Debris in the fuel system may also cause the valve to stay open.

In the diaphram type carb, the valve is very light and small. Gum can easily make it stick.
Engine vacuum basically activates the diaphram and the diaphram is connected to a very small fuel valve. A miniature pump so to speak. If the diaphram gets a hole in it, no fuel.
If the fuel valve sticks. No fuel. If there is debris in the gas, the valve may stay open and the carb floods. The diaphram carb sometimes has a primer bulb attached to it.

Design 3 is not likely in your case.

You already confirmed it's not the gas shut off, fuel filter or fuel pump if equipped.

Some carbs have two mixture screws. One for the idle RPM range and another for high speed.

Both Welcome to the Parts Store and briggsamdstratton.com have engine diagrams on thier website.

The only real cure is to rebuild/clean the carb. This requires disassembly.

I'm not sure of the procedure to set the mixture on the newer engines, but in the old ones, you'd just bottom out the mixture screws and open about 2 turns. Start the engine and adjust until it sounds right.

Cars, on the other hand, in later years cars required drilling out the caps on the mixure screws. I set the idle/mixture using propane gas and a tach which would get the emissions right.

Question / 0n the last n0.3 type carb did you mean the gas tank sits over the carb, or how you stated it " THE CARB OVER THE TANK " for the direct feed ? The tractor was last used in may of 2007 then topped off with gasoline. If it's not gum and varnish then what? Jim

KISS · Dec 8, 2007, 07:33 AM

The carb it literally bolted to the gas tank with a tube into the tank with a screened inlet. The tank is just one big bowl. No fuel valve used in this system. Seen in 3-3.5 HP Briggs engines.

It's a carb problem because you have eliminated the fuel pump and filter. A rebuild kit will probably cost about $15.00. If your afraid to rebuild the carb ask your nearest lawn mower shop, if they will do it for you if you bring just the carb in. They should be able to tell you how to adjust it.

KISS · Dec 8, 2007, 08:56 AM

You can try emptying the tank and use fresh fuel. There could be water in the gas. Also look to see if the plug is wet after trying to crank it, but I assume it's not.

Having been idle since May, suggests the gum and varnish as a real possibility.

NITRO-BTU · Dec 8, 2007, 06:28 PM

Originally Posted by KeepItSimpleStupid

The carb it literally bolted to the gas tank with a tube into the tank with a screened inlet. The tank is just one big bowl. No fuel valve used in this system. Seen in 3-3.5 HP Briggs engines.

It's a carb problem because you have eliminated the fuel pump and filter. A rebuild kit will probably cost about $15.00. If your afraid to rebuild the carb ask your nearest lawn mower shop, if they will do it for you if you bring just the carb in. They should be able to tell you how to adjust it.

Hi, i don't believe i eliminated the fuel pump, i did say there was gas at the pump inlet when the fuel line was removed. However, the gasoline in the plastic fuel tank on the tractor was at the same level as the pump inlet, relative to the engine block. In other words, the gas may have sought it own level being the same as the plastic tank level. Do you still think it's the carb ? Jim

KISS · Dec 8, 2007, 07:10 PM

Post the model number and/or the Briggs engine number, please.

I can't make any suggestions without seeing the unit. Usually sears has a full diagram on the web for almost anything. The engine is definitely at the Briggs website.

If you didn't eliminate the pump, then do.

You can always gravity feed the carb fuel inlet with a hose and funnel. I did that many moons ago with an older car. Put a jug of gas in the engine compartment to get someone home with a bad fuel pump.

If there is an outlet to the pump before the carb, see if you can remove the hose from the carb and pump the fuel into a container by turning the engine over.

Any sort of engine troubleshooting always starts with:

Fuel (simple problems: fuel filter, no fuel and bad fuel)
Air (Simple problems: dirty air filter)
Spark (Simple problems: Spark plug)

NITRO-BTU · Jan 22, 2008, 06:58 AM

Originally Posted by KeepItSimpleStupid

Post the model number and/or the Briggs engine number, please.

I can't make any suggestions without seeing the unit. Usually sears has a full diagram on the web for almost anything. The engine is definately at the Briggs website.

If you didn't eliminate the pump, then do.

You can always gravity feed the carb fuel inlet with a hose and funnel. I did that many moons ago with an older car. Put a jug of gas in the engine compartment to get someone home with a bad fuel pump.

If there is an outlet to the pump before the carb, see if you can remove the hose from the carb and pump the fuel into a container by turning the engine over.

Any sort of engine troubleshooting always starts with:

Fuel (simple problems: fuel filter, no fuel and bad fuel)
Air (Simple problems: dirty air filter)
Spark (Simple problems: Spark plug)

Hello there, the model number is 42a707, series 1238, made in 1997.
I have done a few checks... removed the carb drain plug, and cranked... fuel did spurt from the hole. I really need to know what is the mim. spec. in psi. for the fuel pump.
Next, i sprayed gumout carb cleaner into the main jet, and watched it trickle from the main nozzle. However, the engine still won't start, and will only run on gas primes through the carb.
Please advise, thanks, jim

KISS · Jan 24, 2008, 01:18 PM

The diagram should be here: http://www.briggsandstratton.com/pdf...0%5CMS0635.pdf

I'd suggest rebuilding the carb with the suggested kit. Parts 117 (main jet) and 105. I'd expect it to be the main jet. 117. The float should just be keeping the bowl full of fuel and I think you verified that's happening.

If there was no intake vacuum, you would not draw fuel into the carb either, but then I would not expect the sputter.

In general fuel pumps just keep the bowl full. This isn't fuel injection.

It's NORMAL to have to rebuild the carb, if you don't use fuel stabilizer. You can clean externally until your blue in the face.

NITRO-BTU · Jan 29, 2008, 09:00 AM

Originally Posted by KeepItSimpleStupid

The diagram should be here: http://www.briggsandstratton.com/pdf...0%5CMS0635.pdf

I'd suggest rebuilding the carb with the suggested kit. Parts 117 (main jet) and 105. I'd expect it to be the main jet. 117. The float should just be keeping the bowl full of fuel and I think you verified that's happening.

If there was no intake vacuum, you would not draw fuel into the carb either, but then I would not expect the sputter.

In general fuel pumps just keep the bowl full. This isn't fuel injection.

It's NORMAL to have to rebuild the carb, if you don't use fuel stabilizer. You can clean externally untill your blue in the face.

Hello it's me again, what do you think of using a small wire to run through the main jet orifice, i just don't know what size wire? [ do you ] also, is it possible to fill the carb to the top with a strong carb cleaner... then, letting it soak would this give the same results as if it soaked in an external bath?
After soaking for awhile, then remove the bowl drain nut to drain the cleaner out. The only difference between these two methods that i see is that no internal parts, main jet, idle needle screw, etc. are not removed, but are left in place during the soak. What do you think of my idea, would it be effective? Please evulate, and respond asap. Thanks, jim

KISS · Jan 29, 2008, 11:17 AM

No. Won't be effective. Might be damaging to seals. Cost estimate: < $15

KISS · Jan 29, 2008, 10:06 PM

Now that I'm not replying from my cell, I can elaborate. You have gummy varnish deposits and small passages. You cannot get that stuff off without taking it apart. You cannot get the stuff off, just by soaking. It needs a little bit of mechanical work. There are "O" rings and gaskets and they may not like carb cleaner.

MOWERMAN2468 · Jan 30, 2008, 05:03 PM

Originally Posted by NITRO-BTU

QUESTION / 0N THE LAST N0.3 TYPE CARB DID YOU MEAN THE GAS TANK SITS OVER THE CARB, OR HOW YOU STATED IT " THE CARB OVER THE TANK " FOR THE DIRECT FEED ? THE TRACTOR WAS LAST USED IN MAY OF 2007 THEN TOPPED OFF WITH GASOLINE. IF IT'S NOT GUM AND VARNISH THEN WHAT ?? JIM

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