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.
I may have found something better, a vibra tach. You put it against the engine and adjust it so the reed vibrates the most.
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.
Thanks for telling me that the type of tachometer is called "Hour Meter".
Having said this I decide to get a cheap optical tachometer. The reason is that I have found a way to get access to the spinning part of the engine, and I can use the optical tachometer to measure the rpm of the spinning part of the engine.
the throttle on these small engines is controlled by a GOVERNOR system, when the engine is under light load, the throttle will be more closed, when the engine is under heavy load the governor senses the engine trying to slow down and will open the throttle to tey to keep it running at a constant speed as the load changes. The governor usually is a mechanical setup with springs and rotating weightsw or fan air pressure usually inside the engine that you cannot see. All you see of the governor is a lever that comes out of the engine and is connected to the springs. This level is suposed to move as a fnuction of the engine spped. You have to understand the concept of the governor to troubleshoot these problems. If you disable the goverenor and operate the engine at wide open throttle and no load, IT WILL over rev and can possible fly apart, that can be dangerous. If you don't nuderstand all this., proceed with caution. When you first start it up after any repair, you have to be ready to SHUT ER DOWN immediatly if it starts to over rev. There are many good websites on small engine repair.
Thanks for taking the time to warn me about the danger of letting the engine to spin too fast. Yes, I know about this. This is the reason why I want to get a tachometer to make sure I don't let the engine to spin more than what the manufacturer's has recommended (3600 rpm). So far, just by hearing the sound from the engine, the problem with the engine seems to be running too slow and is not running too fast. The tachometer will arrive in this weekend or early next week just in time as a X'mas gift for myself.
Currently I am suspecting that the spring that is supposed to keep the throttle valve open may have become weak; I am waiting for the tachometer before testing this theory in case I manually open the throttle valve too wide and let the engine spins too fast. Or the throttle lever arm is not setup in the correct position; I checked this once by following the manufacturer's recommended setup and I don't think this is the problem.
The hardest part that I can think of is how to simulate the situation when it is running under load while monitoring the rpm using a tachometer. Currently there is no snow on the ground to test the snow thrower. Even if there was snow on the ground, I would have a hard time using the machine to throw snow while holding the handheld tachometer to point at the spinning part of the engine. I may just have to lift the wheels off the ground with wood blocks, and let the wheels and the snow throwing mechanism to free spin. Seem like a "Hour Meter" is a better device for this test instead of the handheld tachometer that I have ordered. Oh well...
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.
Does turning the needle affect engine speed? If not, it sounds as if a channel is clogged.
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.
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:
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.
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.
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.
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.
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.
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.
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.
Thanks for pointing out that "my simulated load" is just like "no load". As soon as the snow stops, I will try running the machine up the hill (my driveway) while throwing snow at the same time to put it under load to see if the throttle valve will open or not. Seem like I have plenty of opportunity to put the machine (and myself) under load today.
Also thanks for telling me that this is normal for the throttle valve to be closed if the engine is not under load (that is even if we have turned the speed lever to High). I mistakenly assumed that the throttle valve should open up strictly following the speed lever. Thanks for the correction.
As mentioned in another of my post, I find that the engine cannot idle slow. According to other web sites, this means there is likely an air leak somewhere in the engine. Seem like you are right.
The hard part is to find out where the air leak is. And I will need to connect an air regulator to my small air compressor and inject 3- lbs-per-sq-in air through the choke air intake and spray soapy water around the engine to see where the bubbles will come out.
Meanwhile, I will have to start using the snow thrower today and tomorrow regardless the fact that the engine cannot idle snow. I think it should not hurt the engine -- just burn more gas.
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.
I received the snow thrower as a "hand me down" years ago. I was not able to set the speed lever to low. If I tried, the engine would stop. After I cleaned the carburetor a week ago and made adjustment on the high speed mixing needle, I can put the speed lever to low and the engine will continue running. The only remaining problem is that the engine will run in high rpm, not in slow idle speed.
Based on the research on another web site and what have been suggested in this news group, the problem might have to do with air leak. The engine may get air elsewhere from air leak (not just from the air inlet in the carburetor). I don't fully understand this. But I just have to keep this in mind.
Because of the fact that I have been using the snow thrower for years without the use of running it in idle speed, I probably will leave this problem alone.
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).
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