Engine in John Deere Snow Thrower 522 Cannot Run without Choke

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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.
2. 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?
3. 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.
4. 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
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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
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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
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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.
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Jay Chan wrote:

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.
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Jay Chan wrote:

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.
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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
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hr(bob) snipped-for-privacy@att.net wrote:

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.
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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?
2. 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?
3. 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?
4. 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
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Jay Chan wrote:

If there's no snow, I guess you aren't running it under a load. It shouldn't take much throttle to run the engine pretty fast without a load. If there's an air leak, it would take even less throttle opening.

I can't remember if air can be sucked in past a cylinder-head gasket. Why not take a syringe and squirt water around the carburetor and cylinder head? If you can affect the engine speed that way, you've found an air leak.

There could be a passage to add a little gas at low throttle settings. That part could be clogged. (I don't know if your carburetor has such a passage.)

If it's an air leak, the engine may run rich when the throttle stays open to throw snow. With the throttle open, the air leak would matter less and the rich adjustment of the mixing needle would matter more.

engine and adjust it so the reed vibrates the most.
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Thanks for the reply.
I try running the snow thrower under load by the combination of using the self-propel function of the snow throw to run it in high speed, and using the snow throwing mechanism at the same time. But the throttle valve is still closed when I run it under load. There is a V- belt connecting the engine to the snow throwing mechanism. If I turn off the snow throwing mechanism, the V-belt will dis-engage the engine from the snow throwing mechanism, and put the engine off the load. On the other hand, if I turn ON the snow throwing mechanism, the V-belt will engage the engine with the snow throwing mechanism, and I believe this puts the engine under load.

Test didn't reveal where the air leak is. I tested this by using both a feather and the water test. I tested this around the engine, especially in the joint of the carburetor and the engine cylinder. The feather didn't show any air movement when the engine was running -- except near the fly wheel where I believe the cooling fan is.. And the water test didn't slow the engine in anyway. Therefore, I don't know where the air leak is.

There is an "Idle Mixing Needle" and the channel for it. And I have cleaned it and used compressed air to blow the channel. Honestly, I don't know if this matters or not because the problem that I have is with running the engine in high speed; therefore, the idle mixing needle should be irrelevant.

If there is an air leak and the throttle stays open under load, the engine should be running lean because of the extra air. This may explain the reason why the "engine-stall" problem goes away when I open up the high speed mixing needle an additional 1/2 turn to add extra fuel to the carburetor. Is this what you are trying to tell me?

I think I have found what it is called. It is called "Hour Timer" and is connected to a spark plug to count the number of sparks. I have decided to get an optical tachnmeter instead. The reason is that it is cheap, and I have found a way to get access to the spinning part of the engine.
Seem like I cannot determine where the air leak is, and I am not sure if the engine really has an air leak or not. Therefore, I need to get a tachometer to see if the engine can run in high speed or not. If the engine can run in high speed, this may mean I really don't have a problem, and I may just have to accept the fact that the throttle valve cannot open wide. If the tachometer shows that the engine cannot run in high speed when it is supposed to be, this means I really have a problem, and I will try to manually open the throttle valve slowly to see if doing this can make the engine run in the correct high speed (3600 rpm). If the engine can run in the proper high speed when I manually open the throttle valve, this may mean that the spring that is supposed to keep the throttle valve open has become too weak, and the suction from the engine is too powerful for the weak spring and sucks the throttle valve closed. That's despite the fact that the spring "seemed" strong when I manually moved it around.
Because I need to manually open the throttle valve, I am afraid that I may run the engine too fast. Therefore, I definitely need to get a tachometer before I do anything further.
Jay Chan
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Jay Chan wrote:

There's an idle mixing needle! Great! That should help troubleshooting.
When carburetor people talk about idle and high speed, they're really talking about throttle opening. You say the throttle is pretty well closed, so the idle mixing needle should be the most important adjustment.
1. Does turning the needle affect engine speed? If not, it sounds as if a channel is clogged.
2. Can you turn the high-speed needle to where the manual suggests, then adjust the idle mixing needle to run the engine with no choke? If you can, and that adjustment is reasonably close to what the manual suggests, great! No air leak!

Suppose the throttle is closed and the leak adds 10% to the air the engine gets. That will make the mixture leaner. If you open the throttle to let 10 times more air through the carburetor and the leak stays the same, it will be adding only 1% to the air the engine gets, so it won't matter much.
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The engine speeds up and slows down following the adjustment of the idle mixing needle. I guess this means the channel related to the idle mixing needle is not clogged. But adjusting the idle mixing needle only has effect if the high speed mixing needle has opened 1/2 turn more than the manufacturer's suggested initial setting. Otherwise, adjusting the idle mixing needle doesn't have any effect.
I have also tried setting the high speed mixing needle back to the manufacturer suggested initial setting, and then trying to adjust the idle mixing needle to see if I can run the engine with no choke. But this doesn't work. Doesn't matter how I adjust the mixing idle needle, the engine still needs to have some choke (at least 40 to 50% choke). Even with 50% choke, the throttle valve is opening and closing by itself frequently. The only way to make the engine running without any choke and without having the throttle valve opening and closing like crazy is to turn the high speed mixing needle 1/2 turn more open than what the manufacturer has suggested (from 1-1/4 turn to 1-3/4 turn). This is as far as I can manage to achieve; still, the throttle valve is mostly closed.
Having said this, I have a feeling that this may not be a problem for three reasons:
1. The manufacturer suggested setting is just a initial setting. The manufacturer expects us to adjust it. Therefore, the fact that I need to keep the high speed mixing needle more open than what the manufacturer has suggested as the initial setting may not mean that there is anything wrong -- I think.
2. The fact that the throttle valve is mostly closed when the engine seems to be running OK even under load may not mean much. The load that I put on the engine is a "simulated" load, not real load. I am just letting the wheels of the snow thrower and the snow throwing mechanism free spinning. This "simulated" load may not be enough for the engine to open the throttle valve. I will have to try this again with real load when there is snow on the ground.
3. The engine sounds fine when I turn the lever in high speed with no choke. This may mean that the engine is running at the correct rpm. Having said this, I don't quite remember how the engine sound is supposed to be -- afterall, this snow thrower has not run right for two years. I will have to wait for the tachnmeter to use it to confirm if the engine is running at the right rpm.
Therefore, I may not really have a problem -- that's after I have cleaned the carburetor and adjusted the high speed mixing needle.

OK, I understand what you mean. I just don't know how this is related to my situation. Thanks anyway.
Jay Chan
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I have received the tachometer. I immediately try it and find that the engine can run close to the manufacturer's suggested speed (3600 rpm) when I set the speed lever to high speed. But the problem is that when I set the speed lever to low idle speed, the engine still run at high speed (3400 rpm instead of 1700 rpm as what the manufacturer's suggested speed). This means I have a problem.
Doesn't matter I have a problem or not, I will have to use it tommorrow. I will see how it runs when it is under load.

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Don't forget about the points. They can cause symptoms that one would swear up and down were carburetor problems. Maybe your problem isn't in the carburetor at all.
Dan
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I don't know what you mean about the "points". Which parts of the engine are called "points"?
Yes, the problem may not have to do with the carburetor. Now, I am concentrate on the fact that the engine idles fast (not slow). According to other web sites, this likely means that there is an air leak somewhere in the engine.
Jay Chan
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Most likely no points in this engine. Electronic ign.

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Jay Chan wrote:

If it happened to me, I'd dial the tach back to 1700 and see if it showed just one mark. If it's a strobe, it can read 2x, 3x, or 4x the actual RPMs.
If it really is idling too fast, maybe you need to adjust the idle-speed screw. It's a screw the throttle bumps when it closes. All carburetors used to have them.
Each time you unscrew the idle-speed screw a little, you adjust the idle mixture needle for the fastest idle. Then unscrew the idle-speed screw a little more.
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No, the tachometer doesn't have the option to see the number in 2x, 3x... This tachometer shows the actual rpm of the engine shaft, not the number of sparks from a spark plug.
I tried adjustng the idle speed mixing needle; but that didn't make a difference.
In the past weekend, I tested the snow thrower with real load (12" of snow), and I found that I could not make the throttle valve open more than just a little. Anyway, the snow thrower was working fine and could throw snow 20-ft away _if_ the snow was not wet.
At this point, I have decided to live with the minor problem of "cannot slow to idle speed". I could not run the engine at idle speed since I received the snow thrower as a "hand me down". I don't have a need to run the engine in idle speed any way.
After I have cleaned the carburetor and adjusted the high speed mixing needle, I have found the following good things:
(1) I can run the engine without any choke (that had been bothering me for two years).
(2) I can pull start the engine with just one pull. I used to always use electric start because hand pull didn't work before from day one when I received it.
(3) I can put the speed lever to idle and the engine doesn't stop (that I could not do from day one) (the engine is still running in high speed though).
All in all, there are a lot of positive things. Therefore, I am happy with the outcome. And I consider all these positive things as X'mas gifts to myself (in addition to a Rockwell SoniCrafter power tool that I have ordered for myself).
Thanks for everyone who has replied and helped.
Jay Chan
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That is correct, what you describe is basically NO LOAD. Just free turning the wheels and snow screw is NOT a load. It is normal for the throttle to be mostly closed and the enhine running at 3600rpm in this condition. Put the machine on the ground and let it pull itself up a hill... You want the engine to have reserve POWER so that it can maintain 3600rpm even under a heavy load. That means it is normal for the throttle to be NOT full open at 3600 RPM except under the most heavy of loads.
Mark
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