Tecumseh OHSK100 governor linkage setup, governor sag - Snowblower Forum : Snow Blower Forums
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post #1 of 11 Old 02-28-2015, 10:07 PM Thread Starter
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Tecumseh OHSK100 governor linkage setup, governor sag

I have a Tecumseh OHSK100 OHV engine on my blower, model 221608B. I'm not sure if the governor is hooked up properly.

The engine runs very well. But I've noticed the RPM will sag, even when it seems like I'm not putting much load on the machine (it's a 24" bucket). And I've discovered it's not going to full-throttle even when slowing down.

So today I took the covers off and had a look. The attached picture shows how the governor linkage was connected. But when I bought this machine (used), the crankcase breather tube was hooked up wrong. So either the previous owner messed with it, or something happened, but I no longer trust that it's definitely correct.

One link to what I'll call the intermediate governor arm goes to the last hole, furthest out on the arm. But the Tecumseh Technician's Handbook for 4-cycle OHV engines shows a different diagram for my engine's governor, attached picture. I don't know if that diagram is somewhat generic, however.

I drove the machine into 2-foot deep snow, and the engine slowed, but I watched the throttle plate, and it never opened fully. So I moved the governor linkage in by one hole, to match what the Tecumseh manual shows, and tried again. I couldn't say for sure if it was better or worse, I think maybe a little better, but I was busy trying to control the machine. But the throttle still did not open all the way.

I have not loosened the governor's arm on the governor shaft to check that adjustment, but with the engine off, the throttle plate is open all the way, FWIW. So the governor *can* open the throttle fully, at least.

The other thing I noticed is the throttle plate has a tab that presumably acts as a travel stop. There is a casting on the engine which looks like it should be the stop for the tab. It's flat. But my throttle plate tab is long enough that it actually hits the curved casting below that, and looking in the carb, I don't think the throttle plate is quite opening fully.

- Does my governor look like it's connected properly, at that outermost hole?
- Should I try replacing the governor spring, to see if that helps hold the RPM better, with less sag?
- Should the throttle tab actually be hitting the flat area of the casting? I could probably bend the tab to let it travel further.

I'd appreciate any help. If the engine is bogging, while still never going to full throttle (and is therefore not providing full power), well, I'd like to fix that Thank you!
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Name:	Governor linkage, as-assembled.jpg
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Name:	Tecumseh OHV manual, OHSK governor, pg 26.jpg
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Name:	Throttle plate stop tab.jpg
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post #2 of 11 Old 03-01-2015, 11:29 AM
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I think that tab is for your low idle RPM adjust. It looks like when the butterfly moves to the extreme other side that tab is hitting a screw.


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post #3 of 11 Old 03-01-2015, 01:32 PM Thread Starter
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Thank you Shyrp, you're right. That tab is also is used to set the idle position of the throttle Oops.

Great video, thank you!

His governor linkages are somewhat different than mine, unfortunately, so it doesn't answer which hole the governor link should go to.

But at 41 seconds, it looks like his idle tab is cut at an angle on the bottom. And at 51 seconds, it looks like his tab is actually hitting the flat area of the casting, which mine cannot reach.

So if I can get the governor to open the throttle fully, I'll see if I can help the throttle plate to open further on mine. Maybe by trying to cut the tab at an angle. Or, I suppose I could bend the tab to allow more rotation towards full-throttle, and simply re-adjust the idle-position screw as necessary.

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post #4 of 11 Old 03-01-2015, 03:26 PM Thread Starter
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OK, I finally mounted a tach "permanently" to the dash of my machine. So I can watch RPM more easily, and maybe also get a sense of running hours. During testing yesterday, the tach was attached temporarily, and was just hanging on the dash, so I couldn't read it during use.

I adjusted the long arm coming off the governor per the instructions I found online. I loosened the bolt, rotated the governor fully CW, then rotated the long arm fully CW (pulling the throttle plate open), and re-tightened the bolt securing them together.

I re-adjusted the engine to 3600, then again drove it into 2-foot deep snow, the width of the bucket. The RPM dropped (I saw 3150 on the tach), and the governor still didn't open the throttle fully.

I didn't have time to try moving the governor linkage back to the original hole (shown in my first picture). I may try that. I'll probably also try replacing the governor spring, since that's an easy thing to try.

I find it interesting that the engine is likely more powerful than I've been giving it credit for, based on bogging.

I've never taken the cover off and watched the throttle plate on previous 8hp Tecumseh blowers of mine, so I don't know if those were opening the throttle all the way under a heavy load. So, unfortunately, I have no context for this.

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post #5 of 11 Old 03-01-2015, 04:38 PM
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You could try connecting the spring at one of the coils or pulling both ends off and "screwing" it into the hole on one side. That will tighten the spring a bit. If you can see in the side of the carb I would say you should be able to see if the throttle plate opens fully from the inside. Just look and see if it is straight inline with the air intake. If it opens more then 90 degrees it is actually closing itself back up. Also, most don't close to full 0 degrees, so they should probably only open about 80 - 85 degrees.

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post #6 of 11 Old 03-01-2015, 08:18 PM Thread Starter
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Thanks. I ordered a new spring; I'll try putting that on first. If it doesn't do what I want, then at least I'll have a brand-new spring available, and I can mess with the old one, like you suggested, to see if I can improve the performance.

I looked yesterday, the throttle plate is not quite opening fully. You have to look through the carb throat at an angle to line up with the "fully-open" plate. It's not going past-open, it's still in the process of opening.

Of course, I can't actually get it to open fully at the moment, so it's not *really* an issue. But it is impacting the governor adjustment slightly, since the governor and throttle should both be fully-rotated before tightening the governor's bolt. But I don't actually have the throttle all the way open. I don't know how much of a difference that actually makes.

I tried using diagonal cutters on the bottom of that tab, but that didn't work, it's too thick. I can probably cut the tab back with a Dremel if needed, as long as I completely block the carb's intake first. No need to get steel bits into the engine.

Just curious, has anyone else watched their governor open the throttle fully when a heavy load is applied? I'd never given it much thought before now, I always assumed it must be opening fully.

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post #7 of 11 Old 03-01-2015, 08:42 PM
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Quote:
Originally Posted by RedOctobyr View Post
I tried using diagonal cutters on the bottom of that tab, but that didn't work, it's too thick. I can probably cut the tab back with a Dremel if needed, as long as I completely block the carb's intake first. No need to get steel bits into the engine.
Just use a pair of needle nose pliers to bend the tab away from the casting until the throttle plate is open fully.

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post #8 of 11 Old 03-08-2015, 03:43 PM Thread Starter
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I got a chance to work on this today. I Dremeled away the bottom of the throttle plate's tab, so it can open fully (I confirmed that the plate now opens parallel to the carb's intake throat). Then I re-adjusted the governor arm link, for the new throttle plate position.

I installed the new governor spring. It is somewhat shorter than the original spring, which I suppose is good (showing that the original has stretched).

I did also move the throttle linkage back to its original, outermost hole.

After I'd moved the throttle linkage last week, I found the engine was surging after it warmed up (I didn't change mixtures or anything; I can't even if I wanted to, it's a fixed-jet carb). But today, after warming up, it seemed smooth, no surging.

The engine seems to hold RPM better now. I still have about 2 feet of snow in the backyard, and I shoveled a bunch of it into a pile. This loosened it up, and let the machine drive into it more easily (I want to be power-limited, not traction-limited).

I still got the RPM to drop some, but with a 3600 setpoint, I think I saw 3450 while driving into it hard (last week I saw 3150; it's tough to watch closely, though). The throttle still wasn't open fully, but at least the sag seemed reduced.

This improves what you might call the perceived power. The engine hasn't changed, of course, but if it bogs less under the same load, it is effectively more powerful. And it's taking better advantage of what it actually has available. If next winter the sag is bothering me, I'll try shortening the old spring.

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post #9 of 11 Old 03-10-2015, 07:38 AM
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Nice work!! I like to keep mine a couple hundred low to take the stress off it.

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post #10 of 11 Old 12-12-2017, 12:03 AM
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Although this post is a bit old, I wanted to update with my experiences with the same engine in an Ariens ST1024 snowthrower with an OHSK100-221608C engine.


My engine was also bogging down under load with the governor not increasing the rpms so that the engine could keep up with the load. I happened to have a similar blown engine and decide to look into it and took the front cover off so I could look at the internals for the governor (it was a blown rod btw in that one). The weights of the governor spin out as the rpms are increased in the engine, causing it to push the spool down which works on the lever that is connected to the governor arm connected to the throttle's butterfly. But there is no counterforce inside the engine to return the spool back to original position, rather the spring attached to the linkage between the governor arm and throttle plate is what returns the governor back. IMO the governor spring (some sites call it a 'throttle spring') is very important to the proper function of the governor, so that the engine can keep up with the loads it sees. And this spring is stretched many times leading to its fatigue over time and reduced function of the governor.


In my case the governor function had decayed over time - at first I thought the carburetor was not working well and replaced it - but after replacement in the first use the malfunctioning governor became very apparent.


A good way to diagnose it, is to remove the shields around the carb /linkages, run it thru some snow to provide a load (hard to diagnose this without some way to provide a load to the engine that reduces RPMs) and watch the governor arm - if it does not move or barely moves, I would suspect the spring.
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