Predator 9500 Generator backfiring on shutdown.

[ILENGINE]

I see you're a certified B&S engine Master Service Technician. Good to have on the forum. What I know about small I've learned the hard way; other than the training I had in high school (about 50 years ago when rural schools were still funded for agricultural/craft education). I also owned an air-cooled VW for 35 years, which is basically a very large 4-cylinder lawn mower engine. Once you understand how air-cooled engines work, it really isn't hard to keep them running well. Somehow, the importance of being able to tune up an air-cooled engine, or sharpen a chain saw, or set the kerf on a handsaw all took a back seat to pronoun awareness and diversity sensitivity. Meanwhile, we have about 4 generations now that the majority of can't tie shoelaces or look up from their phones long enough to have an intelligent debate about anything.

There is a story behind my MST. Back in 2001 when I first became a Briggs dealer my area rep for Briggs was an A--. So his remarks to me was I don't know when I will be able to get you set up for the 4 day Briggs factory school, but if you take the MST test and pass it you will be exempt from the factory school. At that time the test was a 4.5 hour hands on timed test with a 80% first time failure rate. The day I took my test there was another person that had been a tech for close to 30 years that was taking it for the 5th time.

Anyway I took the test and received an 86% which made me one of only 2 in the state of IL to ever pass the test without going to the school first. And I later becomes friends with the other person which got an 88% on his test So after that the Briggs field rep never give me a hard time.

But like you, I learned to work on small engines by trial and error, mostly error. No formal training as far the basics. Had to do the Kohler and Tecumseh factory schools to become a dealer but no other prior training.

 

[Gord Baker]

Hello this is kind of the sequel to another post I made about a week ago regarding a predator 9500 generator backfiring on shutdown. I have been working on the unit for a family friend. He asked for a full service and a few repairs. One of his complaints was that the generator backfired on shutdown when flipping the shutoff switch. On these generators there are 2 ways to shut them down.. 1:Turn the fuel valve on the front of the generator (proper way according to the manual. 2: Flip the electric shutoff switch (manual states emergency use only.) The customer claimed he had always shut it down using the electrical shutoff switch instead of doing it the proper way. He claimed it started backfiring occasionally on shutdown a couple months ago and now it backfires every time he shuts it down. Generator has 1,690 hours on it and figured a valve adjustment would get back to normal. After the full service (including valve adjustment) the generator would still backfire when it had slowed completely down and was hot.

Because it backfires when the engine has practically come to a stop, and only when it has time to get warm, I assumed it was fuel related. I tore into the carburetor to clean it during the service and the float was not stuck and neither was the solenoid at the bottom of the bowl. I assumed the solenoid had failed internally and was not shutting off the fuel on shutdown like it should. In one of the videos, you can see me testing it with a 12v battery hooked up to my powerprobe. Thanks to some help from ILENGINE on my other forum, I found out that the anti-backfire solenoid runs off power from the generator on shutdown rather than battery voltage like is commonly seen on other small engine applications. In the other video, you can see that it gets plenty of A/C voltage on shutdown but doesn't necessarily continue to provide adequate voltage all the way until the engine stops. Do you guys think it's providing enough voltage until the engine stops? If not, what would be causing this?


What could potentially be the problem here?
Any further diagnostics I could use?
Any thoughts or help is appreciated
Thanks for your time!

Let it come to an idle for a minute or so before shutting down.

 

[Old_Paint]

There is a story behind my MST. Back in 2001 when I first became a Briggs dealer my area rep for Briggs was an A--. So his remarks to me was I don't know when I will be able to get you set up for the 4 day Briggs factory school, but if you take the MST test and pass it you will be exempt from the factory school. At that time the test was a 4.5 hour hands on timed test with a 80% first time failure rate. The day I took my test there was another person that had been a tech for close to 30 years that was taking it for the 5th time.

Anyway I took the test and received an 86% which made me one of only 2 in the state of IL to ever pass the test without going to the school first. And I later becomes friends with the other person which got an 88% on his test So after that the Briggs field rep never give me a hard time.

But like you, I learned to work on small engines by trial and error, mostly error. No formal training as far the basics. Had to do the Kohler and Tecumseh factory schools to become a dealer but no other prior training.

I took a Vocational Agriculture class in high school. The instructor worked out a deal with some of the local small engine shops to supply parts and engines for teaching, both 4-stroke and 2-stroke engines. Back then 2-strokes were pretty much exclusively used for chain saws. He kept a bunch of defective parts around and for our tests, he would put a failed part on the engine or just unplug something and grade us on how long it took to correctly diagnose and repair the problem. At the beginning of the class, he made us disassemble an engine completely and would watch to see if we used the right tools and methods. End of the class was reassembly of one he took apart, and may or may not have put all the parts in the container. It was up to us know if something was missing.

The first time I popped the flywheel off our little mower (because it needed new ignition parts) my folks had a high speed come apart. When they saw how much better it started and ran when I finished, they never took one to a shop again.

Ultimately my curiosity and thirst for knowledge led to an electrical engineering degree, and I still love learning. I hope that never changes. I’m retired now, not so much by choice as physical necessity, so I’m not quite as physically fit for some of the mechanical work. But I still try. I enjoy fixing broke things and making things work. The phrase “It can’t be done” sounds like “Hey yall, hol’ muh beer, hide in the bushes, and watchiss” to me. I’m an educated redneck and love it when I’m underestimated.

 

[Auto Doc's]

I recommend shutting it down using the fuel cut off valve.

I've dealt with too many headaches with anti-backfire valves over the years. Modern fuels gum them up, especially if they sit for long periods in hot weather. (I'm in South Texas)

Personally, I removed the pintle tip off of everyone of mine (riders and generators) and installed manual fuel shutoff valves inline. I do not do that for customers machines.