Engine in John Deere Snow Thrower 522 Cannot Run without Choke

[Jay Chan]

I have a John Deere Snow Thrower Model 522 that has a Tecumseh engine (model HSSK50). Since several years ago, I have been having a problem running its engine without any choke. It will run if I put it on Full Choke or at more than 60% choke. But the engine will stop if I reduce the choke to less than 60%. I was under the impression that this problem means that the carburetor needs to be fully cleaned. Today, I finally have the carburetor fully disassembled and sprayed and soaked the components in carburetor cleaner. And I also replace some parts with parts from a repair kit. But after I have cleaned it and re- assembled it, I find that the problem is still there.

Now that I have the carburetor cover removed, I can see the arms of the various valves of the carburetor in action. I notice these:

1. When the engine is running at Full Choke, the throttle valve is open. I think this is normal because I am running the engine in full throttle.

1. When the engine is running at 80% choke, I notice that the throttle valve is nearly closed. This is odd because I have set the throttle lever to Full (Fast); the throttle valve seems to be closing by itself. The engine "seems" to be running fine. But I have a feeling that the engine "sounds" like it is running in slow throttle. Is this normal? What's sucking the throttle valve from Full to Slow?

2. When the engine is running at less than 60% choke, I notice that the throttle valve is opening and closing, opening and closing, and so on ... all by itself. Therefore, the engine is speeding up and then slowing down, speeding up and then slowing down, and so on... This opening and closing cycle is like just 1.5 seconds. This opening and closing cycle will increase to something like 2 seconds if I slightly open the choke just a bit (something like 55% choke). I don't think this is normal. But I don't know what is causing it to automatically closed and then opened again.

1. When the engine is running at 50% choke or lower (less choke, more open), the engine will stop, and the throttle valve will go back to the full open.

What is going on here? I have checked the spring that keeps the throttle valve at full open (and is the one linked to the throttle lever), and it seems strong enough to keep the throttle valve at full open position if the throttle level is in the Full (Fast) position. What is so powerful that it can suck/push this throttle valve to close?

Is the carburetor needed to be cleaned one more time?

One additional question: The Tech Manual from John Deere asks me to make sure the engine is running at 3600 rpm when the engine is set at high-speed mode. I am under the impression that we don't want the engine to spin too fast and burn itself. That's why we want to keep its rpm to not more than a certain limit. This means I need a tachometer. But tachometer seems to require seeing or touching the spinning part of the tachometer in order to measure the rpm. Unfortunately the engine is fully enclosed, and I cannot see the spinning part of the engine. Is there any tachometer that doesn't require seeing or touching the spinning part of the engine? Can we measure the rpm by timing the number of sparks that the spark plug makes?

Thanks in advance for any help.

Jay Chan

[JIMMIE]

It sounds like you left gas in the tank last season and it cruded up your carb. Applying the choke increases the vacuum pulling the gas through your carb so it makes it run even though you cruded up your carb. Get your carb cleaned. Then use Stabil in your gas from now on.

Jimmie

[Joe]

Good advice. One reason why an engine won't run without a choke is because of an air leak in the intake somewhere and the extra fuel is needed to make it run.. Make sure all your fuel system gaskets are in top shape. Good luck.

Joe

[E Z Peaces]

It's either too much air or too little gas. If it's too little gas from varnish or corrosion in a passage, maybe cleaning didn't remove it. I've had good luck with Sea Foam. I don't understand why it works. It seems to be mineral oil, rubbing alcohol, and a little ether, and you add just a little to your gas.

I think the problem isn't that. I think it's too much air. If it's too much air, you will need less choke when the engine is under a load (actually throwing snow). I'd look for a place air might leak in, on the carburetor or between the carburetor and the intake valve. Loose fastener? Bad gasket? Disconnected tube?

I had a tachometer that you could clip around the spark-plug cable to pick up pulses. If your magneto sparks every revolution, you'll get a reading that's twice as high as the RPMs. I had another tachometer that was a strobe light. You'd make a mark on a rotating part, start the engine, turn the strobe down slow, and speed up the strobe until the mark appeared to freeze.

[E Z Peaces]

Where grass wasn't heavy, I used to throttle my mower down to reduce noise an save gas. Now my mower has only one speed.

I think manufacturers have found that engines that can't be run slow have fewer warranty claims. Keeping the RPMs up can mean better lubrication and cooling.

[ransley]

If by cleaning you mean with spray carb cleaner, that isnt the same as what you soak them in. Are there needle adjustments on the carb, often that is all that is needed. 3600 rpm is a base for most all small power equipment like this, a cheap hour meter usualy has a tach, they have a wire that wraps around the plug wire

[hrhofmann]

It also sounds like the throttle spring is crazy in its operation. The throttle spring should keep the throttle closed and the control should work against the spring to open the throttle. That seems to not be what the original poster described. ALso If the carburetor has really beeen cleaned , then an air leak beteen the curburetor body and the manifold or the manifold and the main engine block is suspect.

Bob Hofmann

[E Z Peaces]

The opening and closing at 60% choke makes me think the problem is an air leak. With 80% choke it gets a good no-load mixture. With 60%, it's too lean, so the engine slows and the governor opens the throttle. With the throttle open much wider, the air leak matters much less. The mixture is better, the engine speeds up, and the governor closes the throttle. Then it's too lean. Vicious cycle.

[bq340]

The tension on the governor spring is set by the speed control & the governor maintains it under varying load.

If an engine is off & the control is set to fast, the throttle will be pulled wide open.

MikeB

[James Sweet]

Usually the banjo bolt that holds the float bowl on clogs, it has some tiny holes around it near the head that you can clean out with some piano wire or something similar. As for the tach, the RPM isn't very critical and you can do it by ear usually, otherwise a stroboscope can be used to measure it.

[James Sweet]

It's more expensive to add the required throttle linkage and most people never use that feature anyway. More often than not, it comes down to nothing more than cost of goods to manufacture, though that isn't as exciting as conspiracy theories.

[ransley]

Slower running engines last longer and run cooler, single speed is cheap to make. 3600 rpm is normal full speed, cut it in half and motor life increases at least 4x. Long life engines run very slow.

[James Sweet]

And require greater displacement to produce a given horsepower. Like I said, it all comes down to cost. People want cheap, and they want enough power to cut their grass. These motors hardly ever wear out before the equipment they power anyway, change the oil yearly which hardly anyone ever does and a lawnmower engine can last 50 years.

[E Z Peaces]

My John Deere LA100 manual says idling or operating at less than full throttle can be harmful. Half throttle should be used only for a warm start or a brief warm-up after a cold start. Full throttle should be used for cold starting, running, and shutting off.

I suppose it has a throttle lever for safety, as a quick way to reduce speed.

[ransley]

An hour rating is better and its from maybe 350-2000 for a cheap Honda, ive worn out a B&S that was well maintained in 350, and I have an 83 Lawnboy thats great. 50 years, with a small lawn.

[James Sweet]

Yeah that sounds reasonable.

I figure most people mow their lawns about 15 times a year, although obviously that depends on location. If a typical suburban lawn takes roughly a half hour to mow, and 350 hours engine life is good for 46 years. Not saying nobody ever wears them out, but I've scrapped a number of lawnmowers due to rusted out decks but the only motors I've ever junked were ones somebody ran out of oil.

[dpb]

Joe wrote: ...

Another prime place on many of the Tecumseh engines is around the throttle axle--they tend to wear out oversize holes in the carb body. Unfortunately, if that's the problem there's no way to fix permanently other than replace.

[mkirsch1]

You are seeing the engine's GOVERNOR in action. The governor senses load on the engine, and opens and closes the throttle to maintain a constant RPM.

When the RPM goes up, the governor closes the throttle. When the RPM goes down, the governor opens the throttle.

It will run at "full speed" with the throttle 80% closed if you are not blowing snow. When you start pushing through a snow bank, the throttle opens up to wide open.

Probably. Some things need to be cleaned again, and it needs to be reassembled correctly. From the sounds of it, the engine is not getting enough fuel. That's why you have to choke it. Choke reduces the amount of air coming in and brings the air/fuel mixture back into balance.

Pay specific attention to the float, needle valve, and seat.

[Jay Chan]

I think you are probably right.

I disassembled and cleaned the carburetor for the second time. This time I soaked the main part of the carburetor (the one that has many holes in it) in carburetor cleaner overnight, and then I used compressed air to blow all the holes in the carburetor (especically the holes where the "high speed mixing needle" is, and I observed that the compressed air could force the carburetor cleaning solution through the holes. It is all clean. But, the engine still exhibits the exact same problem. I have a feeling that this problem has nothing to do with the carburetor being dirty or not. Actually the carburetor was not that dirty to begin with even before the first cleaning. It is no where near as bad as those dirty carburetors shown in YouTube.

I begin to feel that your "air leak" suggestion is probably right because you seem to be able to explain why the throttle valve behaves like what it does now.

Although cleaning the carburetor doesn't seem to help, I think I have found a way to workaround the problem. I turn the "high speed mixing needle" half a turn more open than what the manufacturer suggested, and then I find that I can keep the choke at full open, and the engine doesn't stop, and the throttle valve doesn't exhibit the opening and closing cycle. Therefore, "may" be the problem was as simple as a mis- adjusted mixing needle. But I am not sure for the following reason:

When the engine speed lever is at full throttle, and the choke is wide open, and the engine is not under load, I see that the throttle valve is almost fully closed. I don't know how the engine is getting air under this situation because the throttle valve plate doesn't have any hole in it. The air must be coming from some where. I thought the engine might not need that much air when it was not under load. But when I put the engine under load, I see that the engine speed up and the throttle valve briefly open. But the engine "sounds" like it quickly slows back down and the throttle valve goes back to almost fully closed.

My questions are:

1. Where does the engine get air when it is under load and the throttle valve is somehow closed? Is there a big air leak somewhere?

1. Where is the likely air leak? There is no gasket between the engine air intake and the carburetor. I don't see a gasket there, and the Technical Manual doesn't show there is a gasket either. May be I should try adding some gasket in a tube kind of thing? Other than this, where else is the likely air leak? Does this mean that I need to fully disassemble the whole engine block?

2. The fact is that I can keep the choke at full open after I have adjusted the mixing needle. Does this mean that I have no problem getting fuel from the mixing needle? Does this also mean that dirty carburetor is not an issue here?

1. What is the problem of running this snow thrower as is? I mean running it in full open choke, with the speed lever at high speed, but the throttle valve is somehow closed. Does this mean that the snow thrower will run slow and cannot throw the snow to the proper distance? Sorry, I don't have any snow on the ground to test this.

By the way, can you show me a link to the tachometer that you use to connect to the spark plug? May be I am not using the correct key words to search for it because I cannot find it in the net.

Jay Chan

[Jay Chan]

Thanks for the suggestion. You are right about the engine is not getting enough fuel and the mixing needle needs to be adjusted. As mentioned in my other post, after I have turned the mixing needle an additional 1/2 turn more open than what the manufacturer suggested, I can keep the choke fully opened and the engine will not stop. Seem like this is the way to send enough fuel to the engine. Still, as mentioned in my other post, the throttle valve is somehow closed even though the engine is under load and the speed lever is set at high speed.

Jay Chan