Toro #521 Snowblower surging

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  #1  
Old 02-26-07, 12:22 PM
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Question Toro #521 Snowblower surging

Recently acquired this snowblower from a deceased uncle's estate. Machine is in very good condition, except that his neighbor messed with the carburetor and ??? when he couldn't get it to run.
Cleaned up the entire machine, completely rebuilt the carb, replaced the fuel line, replaced and gapped the sparkplug, changed the oil. Timing is OK, strong spark.
In spite of setting the carburetor jets to factory specs, the engine surges at high speed throttle under no load. Runs fines under load except for soft exhaust detonation.
Have tried everything except for resetting the governor---which I hesitate doing without a factory manual.
I suspect problem is either the combination of carburetor and governor settings or perhaps valves.
Need factory specs for setting the governor.
Any help?
Thanks---
 

Last edited by spider43; 03-03-07 at 07:10 AM. Reason: Delete
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  #2  
Old 02-27-07, 08:37 PM
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I wouldn't mess with the governor yet. I would adjust the carb loading jet. That type of hunting, as it's called, is often too lean a mixture.
 
  #3  
Old 02-28-07, 08:02 AM
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#521 Snowblower Surging

Originally Posted by marbobj View Post
I wouldn't mess with the governor yet. I would adjust the carb loading jet. That type of hunting, as it's called, is often too lean a mixture.
OK---I understand, but if the carb is set too lean, why would the engine run well under load? When the machine is blowing snow, it's fine. If the carb was set too lean, wouldn't the engine stall under load because of fuel starvation? BTW---do you know where I can get a free shop setup spec?
 

Last edited by spider43; 03-03-07 at 07:02 AM. Reason: Delete
  #4  
Old 03-01-07, 07:37 AM
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It has to do with the throughput of the air/fuel mixture of the engine, particularly of a single cylinder, although you would see similar with a multicylinder engine.

Let me give you an analogy. You run down a hill very fast (no load) you over run and stumble (surging). You run up a hill (load). You (like me get tired, but...) are much more consistent in your efforts.

Under load the pulses of the engine are evened out even although the fuel air mixture isn't at its best. The volume of air moving through the engine is affected by the back pressure of the exhaust and the restriction of the air filter, and the processes going on in the combustion chamber. The movement of the air/fuel is for the most part a smooth flow.

Under no load, the volume is reduced significantly and you get more of a pulsing effect. Although you may have the throttle set at full, the governor will only allow the carburetor to open far enough to achieve the max RPM of the engine.

The point is, you are talking about two different carburetor throttle plate openings for the same throttle setting you have used on the control. A drafting carburetor essentially has two fuel setting devices. One for idle and one (loading) for everything else. The latter has to be a compromise in one of the levels typically defined as low, middle and high.

When you get the surging in the middle or high rpm range you can often get rid of it or at least moderate it by adjusting your main jet (loading screw).

Keep in mind as an engine gets older and parts wear, a setting that works perfectly when new may have to be adjusted later in the life of the engine.

In terms of your engine, I would run it under load for several minutes, kill it with the ignition (not the choke) at full throttle, let it cool and pull the plug.

It should be a light brown. If it is gray or a lighter color, set the mixture richer. As always make sure you have the right plug and range of heat for the plug.

An engine can give the impression it's running well if the fuel/air mix falls within a certain range. Optimal is usually considered 18:1. With fuel injection and emission control considerations, that has probably changed. I don't know what those updated ratios would be.

Hope this helps,

Bob
 

Last edited by marbobj; 03-01-07 at 07:47 AM.
  #5  
Old 03-01-07, 04:07 PM
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Originally Posted by marbobj View Post
It has to do with the throughput of the air/fuel mixture of the engine, particularly of a single cylinder, although you would see similar with a multicylinder engine.

Let me give you an analogy. You run down a hill very fast (no load) you over run and stumble (surging). You run up a hill (load). You (like me get tired, but...) are much more consistent in your efforts.

Under load the pulses of the engine are evened out even although the fuel air mixture isn't at its best. The volume of air moving through the engine is affected by the back pressure of the exhaust and the restriction of the air filter, and the processes going on in the combustion chamber. The movement of the air/fuel is for the most part a smooth flow.

Under no load, the volume is reduced significantly and you get more of a pulsing effect. Although you may have the throttle set at full, the governor will only allow the carburetor to open far enough to achieve the max RPM of the engine.

The point is, you are talking about two different carburetor throttle plate openings for the same throttle setting you have used on the control. A drafting carburetor essentially has two fuel setting devices. One for idle and one (loading) for everything else. The latter has to be a compromise in one of the levels typically defined as low, middle and high.

When you get the surging in the middle or high rpm range you can often get rid of it or at least moderate it by adjusting your main jet (loading screw).

Keep in mind as an engine gets older and parts wear, a setting that works perfectly when new may have to be adjusted later in the life of the engine.

In terms of your engine, I would run it under load for several minutes, kill it with the ignition (not the choke) at full throttle, let it cool and pull the plug.

It should be a light brown. If it is gray or a lighter color, set the mixture richer. As always make sure you have the right plug and range of heat for the plug.

An engine can give the impression it's running well if the fuel/air mix falls within a certain range. Optimal is usually considered 18:1. With fuel injection and emission control considerations, that has probably changed. I don't know what those updated ratios would be.

Hope this helps,

Bob
Bob:
Thanks for your reply.
I've already run the engine as you suggested, let it cool, and removed the spark plug. It was light brown.
I understand carburetor function, and I agree with all that you've offered. I've attempted adjusting the "load" jet with little success. I can get the engine to stall (lean) and to load up and quit due too rich a mixture (black smoke, etc.), but can't seem to find an acceptable middle ground where it will run smoothly.
Yes, it's an old machine, 20 years, but knowing my late uncle, was taken care of and never abused. Without knowing how much it had been used by him and his goofy neighbor, it's hard for me to speculate how much wear the engine has sustained.
What really makes me rammy is that I've been servicing and repairing lots of 2 and 4 stroke engines for friend, neighbors, etc. as well as my own equipment for over 30 years. While I've not earned a living doing this, I consider myself a pretty good shade tree mechanic. I've rebuilt and tuned auto engines and transmisions, outboard motors etc. Until now, I haven't encountered any engine I couldn't tune.
That's why I'd like to get my hands on a page or so of the shop manual. This would give me a starting point.
Thanks again for your preceptive response.
Ron
 

Last edited by spider43; 03-04-07 at 11:24 AM. Reason: Delete
  #6  
Old 03-01-07, 06:52 PM
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With a twenty year old engine a lot of wear may have to be compensated for. Some other possibilities would be exhaust obstructions, a vacuum leak or linkage wear or wear within the governor itself. Sometimes, although we like to have things run perfectly, we have to accept functionality as an alternative.

You would get some other ideas, I'm sure, if you posted a request on surging or the hunting issue on the small engine forum, also on this site. That engine you're dealing with, or at least that type, is common in lawn, garden, and other small engine applications. The guys in that forum have a lot of professional experience with your problem and can offer some other perspectives on it.

Should you decide to do that include engine model and other ID information for them. They can zero in on your problem more quickly that way.

Good luck,

Bob
 
  #7  
Old 12-22-09, 11:04 PM
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There are few reasons for this problem, I have put them in the order I
encounter them most. I assume you drained and refilled the gas from
last year and replaced the spark plug:

1. Dirty Carb: Clean or replace it. If you can't replace/clean a
carb, let the pros do it. Frankly, if you are DIY and you can't clean
a carb or look up online how to do it, then replacing is probably
still cheaper than paying a pro to clean it. If you maintain your
engine per instructions, this is probably NOT your problem. If you
didn't know there was maintenance required then uhh ohhh.

2. Sticky Governor Linkage: Lubricate the linkage friction points
liberally with oil and work it to free it up. Possibly replace the
governor linkage spring. Don't be afraid to do this on an old motor
(then see possibility 3). This is a pretty common problem. If the
engine works under load but hunts when the load disappears, this one
is a good bet. If you know what you're doing, you can hold the
governor back a bit and if the engine runs fine at WOT, you're on the
right track.

3. Carb out of Adjustment: Of course, if it ran fine last year, this
is probably NOT your problem.

4. Excessive Carbon Buildup in Engine: Unless the motor has 20 years
of hard, unmaintained service on it, this is probably NOT your
problem.

5. Air leak in engine: Is the spark plug torqued correctly? Is the
intake (carb) or exhaust loose?
 
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