# Tecumseh HSK70 Over-revs shutting off



## Ariens-777 (Dec 8, 2015)

Working on a Toro 724 like the one in the pic. It runs fine at WOT but over-revs when putting the throttle lever in the idle position. Can anyone tell me if the linkage to the carb is correct? Thanks.


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## Jackmels (Feb 18, 2013)

Took this pic from the same model....there should be a idle adjusting screw on the carb that will allow the throttle butterfly to close more to get the desired idle speed.


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## unknown1 (Dec 13, 2015)

Stating the obvious.. you guys are using different holes on the bottom linkage.
I'd be interested to hear if switching that hole makes such a big difference.
I'm still learning about snowblowers and governors and such.


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## 43128 (Feb 14, 2014)

the linkage arms look bent to me


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## Ariens-777 (Dec 8, 2015)

Thanks for the replies. I moved the lower-left rod up to the next hole
and it is still doing it.

Jackmels: can you confirm that the upper linkage goes to the carb
as shown in my picture? I've only seen them go from the carb to the governor. Thanks.


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## Jackmels (Feb 18, 2013)

Top linkage goes to carb. Did you adjust the idle screw on the carb to close down the throttle? Does the Governor kick in at WOT?


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## Ariens-777 (Dec 8, 2015)

Jackmels said:


> Top linkage goes to carb. Did you adjust the idle screw on the carb to close down the throttle? Does the Governor kick in at WOT?


The idle screw was set to just open the throttle. I don't think the
governor is working properly. Got it to idle-down without runaway
RPMs but couldn't adjust the engine speed high enough. I tried to
adjust the governor but it didn't make any difference.


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## Jackmels (Feb 18, 2013)

Governor is probably toast. It is a plastic gear assembly bolted inside the rear crankcase cover. Here's a photo of what it looks like. Not a hard repair, but you'll most likely need a case gasket as well as the governor.


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## nt40lanman (Dec 31, 2012)

I'd disconnect the governor and run it and see if the governor lever pushes harder with more RPM. Post more pics of the arms and governor.


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## Ariens-777 (Dec 8, 2015)

I took the cover off and the governor looks good. I expected to find broken
pieces of plastic but didn't. The spool also lifts when moving the arm.

I am going to change the intake and carb gaskets and then go over the linkages and governor adjustment again. Thanks for the replies.


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## Ariens-777 (Dec 8, 2015)

OK. Comparing the 2 linkage lever pictures, I can tell you that the linkage lever (the one with the holes in it) on mine does not move to the left enough to expose the top mounting screw, even with the throttle lever wide-open. What might cause this?


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## topher5150 (Nov 5, 2014)

very intrested to see what the problem is. I saw some people talking about the linkage. Does it take much damage to the carb linkage to make it run like this?


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## Ariens-777 (Dec 8, 2015)

After more research, I believe the Speed Control Spring, Part #34663 is the
problem. I'll post an update after it comes in and is installed.


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## ELaw (Feb 4, 2015)

I hate to be a downer but in my opinion it's very unlikely that's the problem.

The way that spring works is that when the engine speed control is at a high setting, the spring is put under tension and pushes the throttle plate open. When the RPM increases, the governor in the engine counterbalances the force of the spring and gradually closes the throttle to regulate the RPM at the desired value.

When the speed control is set lower, the tension on the spring is reduced so it pushes the throttle open with less and eventually zero force, allowing the throttle to close further and lowering the RPM. As others have mentioned, there's a screw that limits how far the throttle can close, and if it's screwed in too far the RPM will not be able to go to idle.

There's no way I can think of that the actual spring could fail in such a way that it provides more force when you lower the speed setting. That could possibly happen if the spring were installed improperly, but in that case the solution would be to reinstall it correctly.

Is there any way you could post a video of the behavior you're seeing? It would be very helpful to be able to see what the throttle plate and linkages do as you move the engine speed control from high to low.


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## Ariens-777 (Dec 8, 2015)

UPDATE: the wrong carb is on this engine.


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## classiccat (Mar 1, 2014)

Holy smokes! Glad you figured that out!


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## topher5150 (Nov 5, 2014)

Ariens-777 said:


> UPDATE: the wrong carb is on this engine.


What exactly do you mean by wrong carb?


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## Ariens-777 (Dec 8, 2015)

topher5150 said:


> What exactly do you mean by wrong carb?


The previous owner installed a carb that isn't for an HSK70 engine.

It doesn't work correctly as the carb linkage holes are all in the wrong places and had the effect of keeping the throttle plate closed, rather than holding it open and allowing the governor to control RPM. 

It was slightly opening the throttle plate when shutting it off because the geometry is all wrong.

Take a look at the pic I posted. The carb linkage is hooked to the right of the throttle shaft:









This pic shows the correct carb. See how the upper-right linkage hole is ABOVE the throttle shaft? The wrong carb has the linkage holes to the right of the throttle shaft, not above as it needs to be. This completely messed up the angle of the carb linkage and caused it to not open the throttle plate.









It should be like this (red area with white dot):


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