Briggs 21 HP quits while mowing

[medic2575]

Ok Guys

Every season I have one or two mowers that stump me. This is one of them. Im working on a Craftsman LT 2000 Rider 2008 model. It has the following Briggs Info:
Model
331877
Type
0869-G5
This mower is running me crazy. It will cut for about 15-20 minutes and then it will start cutting out intermittently and will finally shut off for good. Im thinking the coil is probably going because upon it shutting off I immediately check for spark with my trusty in line spark tester and NO SPARK. It cools down for about a half hour and it will fire right back up and repeat the same symptoms. So I put a new coil on it. Same problem, but it will run slightly longer.
Have any of you more seasoned veterans than I ran into a problem like this and where do you think I should go now.
Thanks so much in advance.

 

[Lawnranger]

Is the new coil losing spark, too? If so, then you need to disconnect the kill wire and test again for spark. If you now have spark then something in the kill circuit is causing the problem and not the coil as the coil is just responding to the signal. I'll admit that that is a strange issue but there are also several other causes for the same symptom.

An engine needs three factors present and in the correct proportion to start and run properly 1) the correct air/fuel ratio (fresh, quality fuel is a must), 2) sufficient compression (see manufacturer specification) and 3) sufficient spark at the correct time. If one of these factors is missing or out of proportion, the engine will run poorly or not start/run at all. Your task is to find the missing factor by inspecting and testing the systems involved. Which factor is missing or out of proportion in your case?

There are conditions that will prevent an engine from starting even though all three factors are correct such as a plugged muffler/exhaust but that is not the case here.

You will need a compression gauge to test compression so if you do not have one or do not have access to one you will need to take it to someone who can test it for you. You already have a spark checker. My method of testing for lack of fuel is to spray a shot of carburetor cleaner directly into the carburetor (air filter removed) and try to start the engine. If the engine starts and runs for a second or two and then dies you most likely have a fuel delivery problem.

Perform the necessary tests, report back with your findings and you will receive further advice based on your answers.

 

[Rivets]

I believe LawnRanger hit it on the head when he said, "Is the new coil losing spark, too? If so, then you need to disconnect the kill wire and test again for spark. If you now have spark then something in the kill circuit is causing the problem and not the coil as the coil is just responding to the signal. I'll admit that that is a strange issue but there are also several other causes for the same symptom.". You are going to have to do some electrical testing to find a hot short or hot open.

 

[medic2575]

Ok Lawn Ranger and Rivets. Thanks for taking your time to help me with this. I will jump on those test first thing in the morning and let you guys know what I found. Thank yall both and have a great night.

 

[medic2575]

OK guys. I have tried to get this mower to run until it completely shuts off so I can try the test you all recomended. I run the mower under load while cutting grass and it will intermittently try to shut of to only catch again and run fine for 10 minutes or so and repeat the same symptoms but will never completely shut off. This mower has a line running from the top of the fuel tank to the horn of the intake manifold. I checked that line thinking it may be clogged for lack of a better idea but it is clear. Could my gas cap be not properly venting causing this intermittent problem? I have no idea how to check the cap for proper venting and the cap looks fine. I have already cleaned the carb although it looked real clean throughout. I also disconnected the wire to the fuel anti diesel solenoid that screws into the bottom of the carb and also cut the tip off of the solenoid to surcumvent any problems that the solenoid might be intermittently loosing current and shutting the fuel flow off from time to time. Like I said. I'm lost.
Thanks

 

[Lawnranger]

To diagnose a plugged gas cap vent all you have to do is unscrew the cap about a turn or so and try the machine again. In your first post you said "the engine shut off for good" and now it won't duplicate that symptom but has the erratic running condition still. Have you tried any kind of fuel enrichment while the problem is acting up? You can try adding some choke via the lever to see if the problem goes away. If it does then you know it's fuel related, if not, keep looking. Did you ever disconnect the kill wire from the coil and try running again? Just remember you'll have to choke the engine completely to kill it once the small wire is disconnected from the coil.

Any smoke coming out the exhaust when the problem is happening?