Adjusting governor spring on briggs and stratton engine

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Table of Contents Show

Types of Governor Systems
How Mechanical Engine Governors Work
How Pneumatic Engine Governors Work
What does the spring on the governor do?

The governor system is like a cruise control system. It maintains the speed of your lawn mower or outdoor power products. When Briggs & Stratton governors are adjusted properly, they keep your speed steady regardless of engine load - the amount of work the engine must perform.

When powering a lawn mower, engine load can be affected by hills or height of grass. For a tiller engine, load may depend on depth of the tines while a chipper’s load may be affected by the thickness of branches.

Without a governor, you would need to adjust the throttle manually each time your lawn mower ran across a dense patch of grass. A governor does the job for you by detecting changes in the load and adjusting the throttle to compensate.

Types of Governor Systems

Your small engine contains either a pneumatic governor or a mechanical governor. The main difference between the two is how they detect speed.

How Mechanical Engine Governors Work

To control engine speed, a mechanical governor uses gears and flyweights inside the crankcase to detect changes in the load and adjusts the throttle accordingly.

If you're operating your small engine under a light load, the carburetor needs to deliver a relatively small amount of air-fuel mixture to the combustion chamber. This is all controlled by the crankshaft - which spins quickly under a light load and slowly when the engine is working harder.

When the crankshaft spins quickly, the flyweights open up, putting pressure on the governor cup and crank. This closes the throttle, limiting the air-fuel released into the engine.

When the engine load increases, the crankshaft spins more slowly. This leads the flyweights to relax and the throttle to open back up. Governor springs hold the throttle in the desired maximum speed.

How Pneumatic Engine Governors Work

The speed-sensing device on a pneumatic governor is a movable air vane, made of metal or plastic. This small engine part registers the change in air pressure around the spinning flywheel.

The pneumatic governor also relies on one or two springs to pull the throttle toward the open position. As the load lessens and engine speed increases, air blown by the flywheel also begins to increase, causing the governor blade to pull the throttle plate toward the closed position in its effort to maintain a steady engine speed. The pneumatic governor design is simpler and parts are easier to access.

More questions about small engine governors for lawn mowers & outdoor power products?
Find out if your lawn mower or outdoor power product uses a mechanical or pneumatic governor in your engine manual.

Contact a Briggs & Stratton dealer near you for one-on-one help!

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Hi All.

I've stretched the governor spring on my B&S 3.5HP (093312-0155-E1), running a SB45 cylinder mower. I seem to do this every time I take the cover off to clean the engine. I forget how fragile the spring is

While I'm replacing this spring, I will also add a controller/lever on the handle bar. I'm wondering if anyone has done modifications/improvements to control/adjust the governor? Like, remove the springs and have it all cable controlled?

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Hi all.

I'm having troubles with my engine, mentioned above. I can't lower the idle. Can someone post a link to a website or a manual showing the governor springs, carby, levers etc. I just want to make sure I have everything in place as it should be.

Thanks.

Last edited by Corduroy; 21/04/14 09:33 AM.

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Pushrod Honda preferrer

Most of that manual is a fairly minimal update from the 1984 classic manual, but the 1984 one did not cover Governed Idle, or emissions carburetors. I sometimes find the 270962 manual takes some fathoming unless you have the machine in front of you. In case it helps, most vertical crankshaft Governed Idle engines have their idle speed adjusted by bending the stationary tang at one end of the second (idle speed) governor spring. This is similar to the procedure for adjusting the maximum speed, with the tang at the end of the main governor spring. Note that your main governor spring is Item 209 on Page 6 of the IPL, while your governed idle spring is Item 211. There is a third spring (Item 629A) but it is only a speed control cable return spring, and has nothing to do with the governor: its role is to keep the Bowden cable inner wire from kinking when you reduce the speed.

I suggest that you post some pictures of the governor mechanism, showing the springs, the wire link Item 216, and their attachment points. That will be useful to other members, and will also make it much easier for us to discuss what is wrong.

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Thanks again Grumpy. I see what you mean about the 270962 manual. Over 300 pages.

As you say, it does sound like its just a matter of bending the tag. This seems a fairly basic setup, rather than having a screw adjustment. I assume its to keep the costs down...

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Briggs claimed that it gave better results than a screw adjustment - you could apply a small load to the engine at idle, without its speed changing. It looks to me as if it was cheaper though. Briggs worked very hard indeed at keeping costs down.

Joined: Dec 2013

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Hi All,

I'm still having problems with the idle on my mower. I've installed a new governor spring but the spring doesn't return the throttle to idle.

I've downloaded the manual from this website (over 300 pages) and Section 4, Page 11 is the closest looking diagram but not the exact model. My engine is a B&S 3.5HP (093312-0155-E1).

What I am after is a photo of the governor spring attached to the governor blade. The black plastic part. If someone has one could they direct me to a website, link the photo or email me? or would it be best to contact B&S direct?

Thanks.

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Pushrod Honda preferrer

I'm a bit concerned that you referred to having installed a new governor spring. As discussed previously, your engine has governed idle, so it has two governor springs, one of which controls the engine speed when it is not idling, and one which just controls the idle speed. You can see these springs on Page 6 of the Illustrated Parts List, which you can download here:
http://bsintek.basco.com/BriggsDocumentDisplay/18muvJXEnfBhU7y.pdf

Item 209 is the governor spring, Item 211 is the governed idle spring.

Please post some pictures so we can see what you have and what you have done. Note that the idle speed is only affected by the 211 spring, not the 209 spring. The 209 spring is still required of course, in its original location, to control the engine's speed when it is running at more than idle speed. The idle speed is adjusted by bending the governor plate tang which holds the end of the 211 spring. If the 211 spring is slack when the engine is set for idle speed, it is either incorrectly installed or incorrectly adjusted. We can try to interpret what is wrong when we see your pictures. Until we see them, we are just spinning our wheels.

Joined: Dec 2013

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Thanks Grumpy, reading your comments again, I have mixed the two springs up.

I'll start again so all is clear.....

As I said in my original post, I stretched the governor spring (Item 209) when taking off the engine cover and I have replaced the spring...purchased via the OutdoorKing website

The engine starts, but I can't adjust the throttle (engine speed) via the factory lever on the side of engine. I haven't touched Item 211 spring, so assumed my issue was only related to the Item 209 spring.

I assume now I need to treat these two issues separately.?

Both springs are slack when the engine is running. I understand now how to adjust the Item 211 spring. But not the Item 209 spring.

I was hoping to get a photo of the carby layout to make sure I have everything right. I wont be able to get a photo of my engine until this weekend.

Joined: Jan 2009

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Pushrod Honda preferrer

The 209 spring should be slack when the speed control is in the idle position, because then the engine speed is being controlled by the 211 spring. At any higher speed than that, the speed must be controlled by the 209 spring. If it is being controlled by the 211 spring, or not being controlled at all, with the speed control above idle, something is wrong with the linkage set-up. A series of pictures of the linkage at various speed settings should help us get to the bottom of the problem.

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What does the spring on the governor do?

The governor spring wants to open the throttle and the governor tries to close the throttle. The interaction of the governor spring and mechanical governor holds the throttle at the desired engine rpms based upon a force balance and the load / operating conditions.

adjusting governor spring briggs stratton engine