If it's Not the Governor, Why Is It Over Revving?

Davinci856

Forum Newbie
Joined
Oct 25, 2019
Threads
1
Messages
3
Hi All.

Before anyone asks why I'm going through all the below...this is sort of personal now. I like working on engines, even small ones, because I find it relaxing (usually), but this is bugging the heck out of me.

I have an old (as in 1973) B&S 8HP engine on a Snapper rider (B&S model 190702-0867-01) that worked well for years, but has been sitting for about 4 in a garage after I got a new mower. The new one blew up (threw a rod) so I wanted to use the old rider again for a while rather than the pushmower. It was stored out of gas, so I made sure the air cleaner was in good shape, changed the fuel filter, put new gas in it and it started. Problem is that it ran very fast - (estimate 4000 or so) so I shut it down immediately and looked for a linkage problem. Everything was clear, checked the governor by moving the throttle to fast, saw the governor arm move all the way over, even loosened the locknut after noting where the shaft was, saw the governor shaft smoothly moved through travel from one end to the other, then ended up rotating it in the same direction of fast while the throttle was open all the way and tightened it in the same place it was originally.
I next verified that all the throttle linkages were again in the right places, the butterfly moved correctly with the throttle, I noted positions of the high and low speed mixture screws and then set to a starting point as per the shop manual and started it again. Not as fast as before because it was slightly out of adjustment, but still really fast, so shut it down. Then I got some WD40 to look for what I thought must be an air leak around the carb, but when it was running nothing changed the speed no matter what I soaked with WD40. I found that if I held the throttle with my finger about all the way closed, it will idle sort of normally, but it's not too happy because it's pretty much on choke that way. If I come off of closed with it running even a tiny it (I mean so that you could barely fit a toothpick under the butterfly if you could get it in there) it is off to the races again.
I then thought that something internal must be messed up, but didn't know what. I ordered gaskets and tore the engine down completely. Governor looked to be in good shape, valves were so/so, so I cleaned/lapped/adjusted to spec (which wasn't much different) and decarboned the piston top and head, which were fairly cruddy. I thought maybe something in that carbon might have been the issue, or maybe at least the new gaskets would seal a leak I couldn't find. I even honed the cylinder a bit, but surprisingly could still see shadows of the original hone marks after all these years. After putting it back together, exactly the same situation. It thinks it's a Ferrrari. I remembered that I'd rebuilt the carb not long before storing it, but said since it was really old and a new one was cheap, got a new one and put it on. Still the same.
So, this is where I am now. I know the governor is right, it's got a new carb, and it still races.

Anyone got any ideas?
Thanks.
 

ILENGINE

Lawn Pro
Joined
May 6, 2010
Threads
39
Messages
9,865
Still sounds like a governor issue Either something isn't connected correctly after the carb change, or something is out of adjustment. Could you post pictures of the throttle linkages and make sure to get the connection at the carb to verify that the linkage is in the correct holes.

Would hurt to also make sure that the butterfly screws that hold the throttle plate to the shaft haven't became loose or fell out preventing proper throttle control.
 

Davinci856

Forum Newbie
Joined
Oct 25, 2019
Threads
1
Messages
3
Of course, I agree that it absolutely sounds like a governor problem. This issue is that I can't figure out what in the wrong. I've adjusted governors before and this appears correct. The part that tell me that I don't think it's the governor is that it if hold my hand on the throttle butterfly of the carb it is lower (but still a little high) and then if it only comes up a tiny fraction, it races. I admit it. So far, I've been beaten by a machine made 10 years before my first child was born. This is a simple machine, which is why I am so puzzled.

The pix are pretty terrible - sorry. I really need to pull off the cover and aim down, but the top of the Governor arm is connected to the throttle plate (both the stiff arm and the small spring). The choke is connected to the moveable piece that the throttle cable connects to so that when it's all the way to choke, the choke engages.
The first pic is looking FROM the governor arm are toward the carb. Above the breather tube is the choke arm, and to it's right is the governor linkage with the stiff arm and the spring, which connect to the top of the moveable governor arm.
From gov arm_left is choke arm right is spring and throttle.jpg

The next pic is looking from where the carb attaches to the engine. It shows where the governor arm and spring attach to the throttle plate. The idle speed adj screw to the far right is where I can put my finger to manually bring the idle down to a less terrifying level.
DSC_0776.jpg

I have several more from when I tore the engine down, but these may help a little. Tomorrow I'll pull off the recoil cover and take some better ones if it helps.

Thanks.
 

Attachments

  • Throttle place_top is arm, spring in small hole below.jpg
    Throttle place_top is arm, spring in small hole below.jpg
    80.3 KB · Views: 17
Last edited:

ILENGINE

Lawn Pro
Joined
May 6, 2010
Threads
39
Messages
9,865
Not much to mess up on that setup. if the governor is adjusted correctly that should eliminate that issue. Something else to check is how much slop is in the throttle shaft. that style of carb had issues with wear around the throttle shaft and it would get sloppy and also create an air leak around the shaft.
 

Davinci856

Forum Newbie
Joined
Oct 25, 2019
Threads
1
Messages
3
That was also my feeling originally - that some sort of extra air was getting in that I couldn't figure out.
I thought that spraying the WD40 around while it was running on the original carb would have located it, but was unsuccessful. That's why I spent the $25-ish (if I remember right) on a new carb.

After sleeping on this and since I'll have time this morning, I'll take the recoil off, get a few decent pix and look at it all again because I really believe it HAS to be the governor somehow, despite my certainty that it's right.
I'll search around the Net for a few drawing of what it should look like just in case while drinking coffee, but I made a sketch from memory about what it looks like right now. Maybe I hooked something wrong after taking everything apart? I have no idea, but despite the fact that it looks right to me in how it operates, SOMETHING is wrong.
Does this look right to anyone? Governor Drawing 1.png
 

Attachments

  • Governor Drawing.png
    Governor Drawing.png
    35.4 KB · Views: 17

ILENGINE

Lawn Pro
Joined
May 6, 2010
Threads
39
Messages
9,865
What I normally do is move the throttle to the full position which holds the throttle wide open on the carb. Determine which direction the governor arm moves from idle to full throttle position, and then loosen the governor arm nut and turn the shaft in the same direction as the shaft rotated when moving from idle to full throttle. and while holding the shaft in place tighten the governor arm nut.

I worked a Craftsman a couple months ago that would idle at 2200 rpm and full throttle at 3800 rpm, and did everything I could think of to adjust the governor system but in the end replaced the governor gear. It was like it didn't have enough movement to bring the engine down to idle. This was on one of the newer MTD made in China engines but could apply to your situation also I guess.
 

PTmowerMech

Lawn Addict
Joined
Apr 16, 2018
Threads
387
Messages
2,954
That was also my feeling originally - that some sort of extra air was getting in that I couldn't figure out.
I thought that spraying the WD40 around while it was running on the original carb would have located it, but was unsuccessful. That's why I spent the $25-ish (if I remember right) on a new carb.

After sleeping on this and since I'll have time this morning, I'll take the recoil off, get a few decent pix and look at it all again because I really believe it HAS to be the governor somehow, despite my certainty that it's right.
I'll search around the Net for a few drawing of what it should look like just in case while drinking coffee, but I made a sketch from memory about what it looks like right now. Maybe I hooked something wrong after taking everything apart? I have no idea, but despite the fact that it looks right to me in how it operates, SOMETHING is wrong.
Does this look right to anyone? View attachment 46010

The heavy spring that's connected to the plate, can you not bend the plate the spring is connected to?
 

sgkent

Lawn Addict
Joined
Sep 27, 2017
Threads
30
Messages
1,679
an engine needs air and fuel to race like that. The air is getting into the cylinder somehow. If the butterfly is closed, and you can see that then it is coming from somewhere else. If it were a 2 stroke I would say look at the crank seals but most likely it is a 4 stroke. Try using some carb cleaner, the flammable kind, or some Berrymans around the engine area instead of WD40. See if you get any RPM change. You can use windex or water too because it will cause it to run different or die. I am willing to be that if you put your palm over the carb inlet it still runs. If not then it is a carb issue where something is holding the throttle plate open. Normally that would be the governor but you say you can see the throttle plate completely closed when it happens.
 
Last edited:

cpurvis

Lawn Addict
Joined
Aug 25, 2015
Threads
21
Messages
2,256
Worn throttle shaft or throttle shaft bushings can cause a lot of problems but not the problem described in the original post.
 

bertsmobile1

Lawn Royalty
Joined
Nov 29, 2014
Threads
64
Messages
24,647
Start the engine and work the governor arm by hand.
If you can keep the engine running at the correct speeds then it is a governor problem.
As the engine is a bit long in the tooth it could just be that the governor spring has stretched a little bit.
 
Top