Briggs Hot Start Problem

[Mek-a-nik]

Customer has a 31P777-0299 E1-041118 ZE. It's on a Craftsman Tractor. He's owned it since new and takes pretty good care of it. For a while now (2 years), it will not restart until it is cooled off. It has spark when it does it. Still, because of its age, he agreed to a new mag, and it still does it.
Besides the mag, I have opened the valve adjustment to I- .008 and E- .009, just in case the valves aren't closing all of the way when it heats up.
I also swapped carbs with another tractor he has to see if maybe a rich condition is occurring. It is the same carb.
I thought maybe he was using the choke even when hot, flooding it, but he'd been starting it for 8 years or so without a problem. So he knows how.
It has 133# compression cold. Seems high, but the MCR is working and it's not hard to crank, even with the lash opened.
One thought I had while typing this is; maybe the MCR is holding the valve open when it's hot? If it is, it does it consistently, as it will not start hot every time.

[KE4AVB]

Have tried a known good plug? I have had a few that would not fire under compression when hot.

[HondaG100]

Have you checked compression while it's hot?

[Mek-a-nik]

Have tried a known good plug? I have had a few that would not fire under compression when hot.

This runs until you shut it off, then won't start until it cools off. Would that count? I'll try a different one, but I think he has, too.

Have you checked compression while it's hot?

No, good idea.

I don't go back until next week, so I'm collecting ideas.

[Arkie]

I just flogged a aggravating Briggs l-head opposed twin (valves in head) engine that would not start sometimes after it had been run quite awhile. Seemed like it would not re-start right when the mower was really needed to finish a job and when getting ready to test ignition it would start. The spark was also weak when the engine was cold and the engine would start ok cold. I got on the right track by comparing the spark to a good engine. (and taking time out to fix my own aggravating engine)
I used a Briggs 19368 ignition tester and found that the unit had weak ignition. (also use a inline flasher type light ignition tester but the Briggs actually showed the weak spark jump across the gap. Place a piece of black tape over one side of the viewing window so as to have a black background when viewing the spark or look at the spark in a dark place, not bright sunlight. I kinda ignored the weak looking spark because the engine would run great once it started and sometimes while testing the ignition. When viewing the spark on the 19368 tester you could just barely see a small narrow spark leaving the plug wire end and could not see the the arc all the way across tip to tip of the tester. A good spark can be seen like a bolt of lightning all the way across tip to tip across the tester gap, when cranking and also with the engine running. The spark should jump across a 3/8 inch gap easily. I've spread the gap on a spark plug and other Bubba methods to test for spark but the 19368 is more user friendly.
the thread is here: http://ppeten.com/forums/viewtopic.php?f=3&t=1371

[KE4AVB]

Arkie's recent problem had reminded of a problem I have had a few times on other Briggs engines. Check the kill wire for the magneto. I have seen a few where they were pinch between the starter and the crankcase that would ground out after the everything is good and hot and return to normal when cooled. When you shut down the engine it would continue to heat up for short time and this might cause problem.

[Mek-a-nik]

Arkie, I followed your thread about the spark problem. Interesting. I always thought that an electronic ignition magneto either worked or it doesn't. I've seen points magnetos act funny. I never considered a pinched kill will. I will check it out on this tractor.
Come to think of it, I did see that on a 2 stroke a few years ago. It wouldn't spark on the Briggs tester, but would using the "cheapo" kind with the bulb in it. I think in that case though, it was a bad mag. There is a use for those things...

[Arkie]

Arkie, I followed your thread about the spark problem. Interesting. I always thought that an electronic ignition magneto either worked or it doesn't. I've seen points magnetos act funny. I never considered a pinched kill will. I will check it out on this tractor.
Come to think of it, I did see that on a 2 stroke a few years ago. It wouldn't spark on the Briggs tester, but would using the "cheapo" kind with the bulb in it. I think in that case though, it was a bad mag. There is a use for those things...

My thoughts also about magnetos and ignition and that is main reason why I checked everything else first. Fuel, valve lash twice, compression, and when I would start to check the ignition spark it would start and run ok and I would quit testing and go mowing until it quit again.
The real life saver was when I had the one good engine I decided to just transfer parts. The good starting engine was one that should have gave starting issues, it was just thrown together, been sitting outside for over year and I just purchased it for parts for $25, intake valve was stuck, I got a used valve, lapped the valves, installed the heads with the used head gaskets and just hung it together for a test run, intake valve seat popped out, staked it into place couple months back and used the same old head gasket, had to ultrasonic clean the carb and install a pump kit and when it ran ok I installed it onto a yard tractor with no deck and a trailer behind for yard clean-up and hauling tools. The ole junker engine just kept running and starting like the energizer bunny, the engine I really needed was the aggravater.
The engine is now starting ok when hot.

[Mek-a-nik]

Yeah, I see so many pieces of equipment that are in amazingly bad condition and they just keep right on going. Makes maintenance a tough sell on lower end equipment. Why spend to maintain a $200 mower when it'll just keep running?

[Mek-a-nik]

Looked at this again today.
No crimped wire.
140 psi comp cold, 175 psi comp hot.
I put a new plug in it. It had a "FirstFire" in it. I think FF22. The owner said that's what Sears sold him for it. I couldn't hang around long enough to see if it helped. (Mobile biz.) He'll report back to me.