B & S Engine Mower Running Rough

[Kennykenny]

This is an autochoke engine, right? No primer bulb? If so, I think that's the problem. Either the autochoke linkage is hooked up wrong, or the actuator spring on the muffler has failed.

Yes, it is an autochoke. No primer bulb. I am attaching pics of the engine/carb. The revving of the engine is surging and slowing down, surging and slowing down continously but not at full throttle. It doesn't normally run semi-smoothly upon initial start. As previously mentioned, the mower is hard to start and it takes a bit before it runs semi-smoothly at all.

You mentioned about either the autochoke linkage is hooked up wrong, or the actuator spring on the muffler has failed. If you still think that these are the issues after my additional information, is it possible to provide me how to on fixing these scenerios?

Thanks so much for your help!!

 

[primerbulb120]

Start the engine and try moving the autochoke lever manually to see if it makes a difference. The autochoke lever is the large, black plastic lever that opens and closes the choke valve on the carburetor. The choke should open when the engine starts and stay open as it runs. You can remove the air filter to verify that the choke is opening all the way. If it isn't opening all the way, that could be your problem.

I noticed in your second picture the linkage return spring is disconnected. (Stretched silver spring. This is not the actuator spring.) Did you disconnect it for pictures, or was it disconnected to begin with?

 

[Kennykenny]

Start the engine and try moving the autochoke lever manually to see if it makes a difference. The autochoke lever is the large, black plastic lever that opens and closes the choke valve on the carburetor. The choke should open when the engine starts and stay open as it runs. You can remove the air filter to verify that the choke is opening all the way. If it isn't opening all the way, that could be your problem.

I noticed in your second picture the linkage return spring is disconnected. (Stretched silver spring. This is not the actuator spring.) Did you disconnect it for pictures, or was it disconnected to begin with?

I had done as you said previously and moved the lever to open the choke valve. Opening the choke does help make the moter run at a higher RPM. When I let go the rpm goes down. Yes I did remove the spring to take the picture. It had been attached.

 

[primerbulb120]

If you start the mower and attach a zip tie to keep the choke open, will it run properly or does it still sputter?

(Just make sure you don't zip tie the throttle open - your engine could explode! The choke valve is the one nearest to the air filter. Throttle is closest to the engine.You probably already know this, but I'll mention it anyway in case some less knowledgeable person sees this thread.)

 

[Kennykenny]

If you start the mower and attach a zip tie to keep the choke open, will it run properly or does it still sputter?

(Just make sure you don't zip tie the throttle open - your engine could explode! The choke valve is the one nearest to the air filter. Throttle is closest to the engine.You probably already know this, but I'll mention it anyway in case some less knowledgeable person sees this thread.)

The choke valve is the flap inside of the carb that opens/closes? Right? You just have me wanting to make sure after your comment of the engine exploding...:smile:

 

[primerbulb120]

There are two flaps (butterfly valve is the technical name) in the carb. One is the throttle, other one is the choke. I circled them in the picture to show you which one is which.

The choke should be closed when the engine starts and all the way open when the engine is running. The engine won't start cold with the choke open, so what I would do is:

1. Zip tie the choke fully open.
2. Put a quick shot of starting fluid in the carb throat to prime the engine.
3. Start engine and see if it runs better.

 

[Kennykenny]

View attachment 31822

There are two flaps (butterfly valve is the technical name) in the carb. One is the throttle, other one is the choke. I circled them in the picture to show you which one is which.

The choke should be closed when the engine starts and all the way open when the engine is running. The engine won't start cold with the choke open, so what I would do is:

1. Zip tie the choke fully open.
2. Put a quick shot of starting fluid in the carb throat to prime the engine.
3. Start engine and see if it runs better.

Here is the pic using a zip tip following your directions. Following a couple squirts of carb cleaner inside of the carb, it took about 6 pulls to get the mower to start. I let the mower run for about 30-45 seconds. The engine ran the same way as it was doing prior, low rpm's, slow surging of the engine and then back down and then repeat. The only way that the rpm's would increase was to pull on the spring that is attached to the throttle, pulling the spring toward the front of the mower. I turned the mower off and tried to start the mower again(with the zip tie still keeping the carb flap open) and it wouldn't start. I sprayed more carb cleaner in the carb and it took about 10 pulls to start the engine and it ran the same way as before.

Thoughts? BTW, great visual that you provided in the last response. That helped a lot!!!

 

[primerbulb120]

Hitherto, I have been giving you one thing at a time to check. However, this is too slow of a process for both of us. Therefore, I will give you a list of all the things I would check. It may look intimidating, but it will probably take you less time to do everything than it has taken me to type this list. :wink:

1. Make sure the mower blade is installed properly and in good condition. Make sure the blade adpator cannot spin on the crankshaft. The mower blade acts as a secondary flywheel, and the mower will exhibit the symptoms you describe if the blade is missing or excessively worn. Be sure to tip the mower so that the carb is facing up to prevent oil from draining out the crankcase breather.

2. Did you drain and clean the gas tank before reinstalling the carburetor? If not, drain it and clean it with fresh gas. Make sure the fuel line is free of obstructions. Then drain the gas from the carburetor and re-assemble everything. Bad gas or an obstructed fuel line can cause the symptoms you describe.

3. Make sure the three inlets in the carburetor bowl bolt are all clear of obstructions. The passages within the bolt form a "T" . If one or more of them are clogged or obstructed the engine will exhibit the symptoms you describe.

4. Ensure that the spark plug is gapped correctly. I would set it at 0.025 inches.

5. Attach an inline spark tester to make sure the magneto is working properly. If you don't have an inline spark tester, skip this one for now, as it's one of the less likely causes.

6. Remove the muffler and see if the engine runs smoothly without it. If so, you have a clogged muffler.

7. Ensure that the O ring behind the carb is in good condition.
:thumbsup:
8. Inspect the intake tube (plastic tube from carb to engine) and ensure that it is free of cracks. Make sure the bolts holding it to the engine are not loose. You will have to remove the metal shroud to do this.

9. While you have the metal shroud removed, make sure there is no debris preventing the governor and throttle linkage from operating properly.


10. Inspect the head gasket to make sure it's not blown. Ensure that all cylinder head bolts are tight.


If none of these are the problem, I'll suspect one of three things: sheared flywheel key, bad carburetor or valves not seating properly.

If you could take a video of the engine running for me to listen to, that would also help. History of the problem would also help. (Did it begin while you were using the mower, or did it begin after the mower was in storage for a while?)

If you need any help with the items on my list, let me know. I assure you, these inspections/repairs are easier than they sound.:thumbsup:

 

[Kennykenny]

Hitherto, I have been giving you one thing at a time to check. However, this is too slow of a process for both of us. Therefore, I will give you a list of all the things I would check. It may look intimidating, but it will probably take you less time to do everything than it has taken me to type this list. :wink:

1. Make sure the mower blade is installed properly and in good condition. Make sure the blade adpator cannot spin on the crankshaft. The mower blade acts as a secondary flywheel, and the mower will exhibit the symptoms you describe if the blade is missing or excessively worn. Be sure to tip the mower so that the carb is facing up to prevent oil from draining out the crankcase breather.

2. Did you drain and clean the gas tank before reinstalling the carburetor? If not, drain it and clean it with fresh gas. Make sure the fuel line is free of obstructions. Then drain the gas from the carburetor and re-assemble everything. Bad gas or an obstructed fuel line can cause the symptoms you describe.

3. Make sure the three inlets in the carburetor bowl bolt are all clear of obstructions. The passages within the bolt form a "T" . If one or more of them are clogged or obstructed the engine will exhibit the symptoms you describe.

4. Ensure that the spark plug is gapped correctly. I would set it at 0.025 inches.

5. Attach an inline spark tester to make sure the magneto is working properly. If you don't have an inline spark tester, skip this one for now, as it's one of the less likely causes.

6. Remove the muffler and see if the engine runs smoothly without it. If so, you have a clogged muffler.

7. Ensure that the O ring behind the carb is in good condition.
:thumbsup:
8. Inspect the intake tube (plastic tube from carb to engine) and ensure that it is free of cracks. Make sure the bolts holding it to the engine are not loose. You will have to remove the metal shroud to do this.

9. While you have the metal shroud removed, make sure there is no debris preventing the governor and throttle linkage from operating properly.


10. Inspect the head gasket to make sure it's not blown. Ensure that all cylinder head bolts are tight.


If none of these are the problem, I'll suspect one of three things: sheared flywheel key, bad carburetor or valves not seating properly.

If you could take a video of the engine running for me to listen to, that would also help. History of the problem would also help. (Did it begin while you were using the mower, or did it begin after the mower was in storage for a while?)

If you need any help with the items on my list, let me know. I assure you, these inspections/repairs are easier than they sound.:thumbsup:

Thanks. I will let you know.

 

[primerbulb120]

I'll stay tuned. Whatever you do, don't assume that my list is too hard because it covers the whole page. :laughing: