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Discussion Starter #1
I'm fixing a couple of mowers for a friend. One is a B&S 4.5 on a Bolens 21 inch push mower. It has the plastic carb on it. I did a oil change, plug, air filter . It had been sitting a year or so and would not start. I got it to start and die several times. Took the tank and carb assy off and separated the carb from the tank. I cleaned the passageways in the carb with carb cleaner and some comp air. Re-assembled it and put it back on the mower. Starts fine now, but runs at a high rpm. Not quite to where you'd think the governor was stuck or kicking in. Seems awful fast for this type of carb. THere no speed control on this mower at all. It must run at one speed. I checked the linkage to the governor and it works fine. Just seems too high for me. Any ideas or suggestions?
 

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If the linkage moves free and isn't bound up there should be a spring going from the governor rod to a tab on the front of the tank bracket. If you bend that tab you should be able to adjust idle up or down. A little goes a long way and its very easy to bend when you take the tank and carb off. Hope this helps.


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Make sure the legs on the throttle lever are on either side of the stop tab on the carb body, they have a tendency to skip over the little tab..
 

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Discussion Starter #4
The legs are where they should be, I had one do just that before. It raced up real fast. I will bend that tab slightly and try that. It's just too fast in my opinion. It's amazing how cheap they've gotten. No mechanical throttle control at all. I guess they depend on the governor to speed up under a load while cutting.
 

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Discussion Starter #5
Update- I bent the tab to increase the spring tension, but no effect, it still races. I looked at the governor rod and linkage, it moves freely. I've never seen a mower without some type of throttle. THis one has the rod from the carb, which goes to a pivot and on the back side of the engine is the governor. All that is free. I have another carb I can try, but I don't think it's going to do anything. I wonder if it has anything to do with the fact that the blade was curled down on one side and the bolt holding it to the engine was loose. They won't admit to hitting anything, but the evidence was there. I checked the keyway, it's right where it should be. I'm wondering if it jammed the governor or broke it inside. But all that is moving freely on the outside. Anyone know where I can find a repair manual on these B&S engines? B&S only has the op and parts manuals available.
 

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You want to decrease spring tension, to lower engine speed...

If you were maybe a little rough on it, when removing the carb from the rod..it may have moved the governor lever on the back of the engine, on its shaft...
 

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Discussion Starter #7
The spring tab was bent towards the carb quite a bit. I brought it up about a 1/4 inch I'll move it back to the original position. The rod goes to a pivot and that allows it to go around the corner to the governor.
To adjust the governor, do I loosen the nut and then turn the governor rod to the left while holding the arm to the left? I can't seem to find a repair manual online. It's a 2009, so you'd think even B&S.com would list it. I guess they'd rather you took it to a shop. I'm that shop.....sort of.
 

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Is your 4.5 like the older 3.5?

hey bonusbuilt, maybe you could send a picture of the carbureator with the A/filter removed so we could see what you have. On the older 3.5 hp engines the plastic carb. was mounted directly to the gas tank, the carb. also had a primer bulb...is that about what you have?

On those motors I usually look for a cracked or loose mounting of the plastic intake manifold pipe. I also verify that on the carbureator, (where is slides onto the pipe), there is a "o" ring, but even if the O-ring is there, there also is a plastic O-ring retainer than must be snapped fully in place, it fits into the carbureator body at the mounting area where the pipe goes into it, it retains the O-ring. Make sure the metal shroud that covers the flywheel is not dented from something being dropped on it, a bent shroud would cause the air vane of the governor to hang, and cause an overspeed/incorrect governed action. A mouse nest under the shroud might cause the same thing but you already said you checked the flywheel key...so I doubt you have that problem. If you have a mechanical governor, make sure the lever is not binding while the engine is at rest.

Ummmmmmmm ya your right, the governor controls the speed in relation to the load. If it is running too fast, you should be able to slow it down by adjusting that tab. But that is rarely ever necessary unless someone has already bent the tab, for more speed!!! ohhhhhhh yeah LOL

wwxx
 

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Discussion Starter #9
It is an older plastic carb that is bolted directly to the tank. The tab was bent down enough so there wasn't alot of tension on the spring. I did blow alot of acorns out from under everything. The o ring is there and the retainer. I'll check the tube and make sure it's ok. I am going to look closer at the governor linage. It looked ok, but I will check again. THere isn't an air vane on it. It has a rod that goes from the carb to a pivot so it can go around to the back of the motor where the governor is. I'll post some pics tomorrow.
 

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probably a bent crankshaft

hey bonusbuilt, I think you said the blade was bent, did you replace the blade with a new one, and more importantly is the crankshaft warped? The intense vibration from an out of balance blade/slightly bent crankshaft will cause all kinds of engine speed trouble, especially with carbureator/gov. linkage/spring of that type. Typically a bent crank will show signs of faster than normal speed, and while running on concrete floor the thing will literally try to walk away~~from the incorrect vibration.

To adjust the static governor linkage, while the engine is turned OFF, loosen the clamp on the governor lever, move the governor linkage back & forth several times at the carbureator throttle, from idle to wide open, notice which way the the governor lever moves each time you move the linkage to wide open. Hold the linkage in the wide open position, turn the governor cross shaft back & forth then turn the shaft fully in same direction as if moving it toward wide open, hold the cross shaft & lever (both) in the wide open position tighten lever clamp. Test that the lever & throttle move freely back & forth.

I don't need a picture now, that I know what your set up is.

wwxx
 

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Discussion Starter #11
Success! OK, I don't quite understand how the governor got so far out of wack , but I adjusted it and it runs at a regular speed. THe cover looked like it had never been off, but now I have my doubts. When they hit whatever it must have jarred things pretty good. the blade was dragging on the ground with the wheels at a high setting! guess I learned a few things on this one, for sure!! THanks to Red and WWXX who helped me with what to look for. Every one I work on helps me understand small engines better.
 
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