Briggs engine kicks back when starting, runs rough, hard to start. But Ignition module, spark plug, flywheel key are fine?

[TylerFrankel1]

Hello all! I am working on a mower for one of my neighbors, that can't get it started. I took it back to my garage and started looking it over. Something is a bit off of it. It's a 650 series briggs 190cc L head. The pull rope does not have as much length as I would expect, and there's a plastic piece missing where the pull rope handle meets the cooling shroud. I feel like it's possible someone else worked on it before, which would explain its strange behavior, which I'll get to in a minute.

Of course I suspected the carb. I fixed one just the other day for someone where as usual, it was just bad gas/plugged carb. I dropped the bowl and checked the jet, but they were pretty clean and there was no corrosion. So I put it back together and checked for spark. There was spark. I then took the air filter off and was greeted by the MOST dirt I have ever seen. It was packed so tight that the fins of the filter weren't visible, it was a smooth rectangle of dirt. I figured that was the problem, and tried starting it with no filter. It would start to kinda go, but it kicked back a bit and I swear I could see exhaust coming out of the intake. After pulling hard for a few minutes I got it to start, and it runs rough. It revs up and down rapidly like it's surging, but also sounds strange. I then assumed it was the flywheel key. I checked the blade, and it is ever so slightly off balance, but not badly. I checked under the starter cup, but the key is fine. So I tested a new spark plug, gapped properly. Still ran badly. I tested a different ignition module. Still ran badly.

I was pretty confused at this point. I took off the head to look at the valves and piston. The piston and cylinder look ok, and the valves seat firmly when they should. The compression release is working too.

With the kill wire removed, I put the engine brake on and it smoothed out a bit with a load, still not perfect.

Everything I know to check is exhausted at this point, spark, ignition, timing, valve seating, carburetor, etc. are ok. At this point, the only thing I can think of is MAYBE someone else rebuilt this engine at some point and put the camshaft in wrongly (lined up timing gears wrong). Before I take it all the way apart, however, I just wanted to get other opinions. Anyone have ideas?

Thanks!

 

[Rivets]

Did you check the float level? I’m thinking being that dirty, the carb has been sitting around with old fuel and the seat has swelled, creating a lean running condition.

 

[tom3]

Still sounds like a lean condition. Try getting it running and put your finger over the carb intake enough to choke it some, see if it smooths out.

 

[TylerFrankel1]

Figured it out. I'm an idiot. The key was sheared after all. It sheared at an angle so that it looked whole on the top, but wasn't really. In fact, it was almost 1/5 of a turn off. I can't believe it ran at all. I'll go replace it tomorrow. I decided to check one of my other engines that is running rough to see if I should order more than one key, and it looks like this:


Is that serious enough to be a problem or can I leave it. This one runs rough like I said, but I wouldn't think this is too too severe. Flywheel wasn't coming off when I hit it with the old hammer and chisel, so I stopped because I don't want to damage it. I broke the flywheel on one of my scrap engines hitting it hard, so I stopped prying until I get an opinion as to if there is even a reason to.

 

[Rivets]

That one is starting to shear, I would replace it also.

 

[ILENGINE]

Think about it this way. The key is offset which is advancing the timing about 6 degrees so instead of firing at 22 degrees BTDC it is now firing at 28 degrees BDTC.

 

[TylerFrankel1]

Good to know, thanks. I'll try and get the flywheel off without using the chisel and hammer. Maybe I finally invest in a proper puller.

 

[PTmowerMech]

Put a pry bar under the fly wheel, screw the bolt back onto the crank until the crank is about 1/4in below the top of the nut. Then give it a whack or two. (the nut) It should pop off without having to hit it too hard. Easy peasy, japaneasy.

Just make sure you got the pry bar on something pretty solid. Taryl makes a pretty good video about this if you're unsure.

 

[StarTech]

I just cringe at the thought doing this on today's thin crankcases and ultra light flywheels. I havedone split in two flywheels and hole in crankcases where a DIYer use the pry bar trick.

Just a note some the holes for pulling do need to be tapped for first time use.

 

[Tinkerer200]

P have

I just cringe at the thought doing this on today's thin crankcases and ultra light flywheels. I havedone split in two flywheels and hole in crankcases where a DIYer use the pry bar trick.

Just a note some the holes for pulling do need to be tapped for first time use.