Will not start after engine is hot

[kinsler33]

The traditional problem in a Briggs and Stratton engine that won't start when hot is that the valves are out of adjustment. As the engine wears the valves sit lower in their seats and they'll leak slightly when the engine is hot because the valve stems expand with heat. An engine so encumbered will run but not start, at least not willingly. Your car doesn't have this difficulty because its valves adjust automatically, but a small four-stroke engine needs an occasional valve adjustment. When I last did this I fashioned a feeler gauge out of a plastic bubble pack and gently applied a file to the valve stems, for the older B&S engines don't have adjustable valves. Yours may be improved in that regard.

Mark Kinsler

 

[bertsmobile1]

Because of idiot emission laws mower engines are jetted way too lean.
The volume of fuel sucked into the engine is a function of how fast the air is rushing past the venturi in the carb & the height of the fuel in the float bowl .
When running at idle the engine is doing something like 1500 rpm
When pulling the starter cord you would be lucky to be doing 500 rpm
So the slightest constriction to the idle circuit will mean there is not enough fuel to start the engine
From cold you have a primer which will squirt some fuel directly into the carb throat or raise the height of the fuel in the float bowl so it is easier for the air rushing past the venturii to suck fuel up into the carb throat.
The joke of this is every push mower in the entire USA running 24/7 for an entire year would not put out as much pollution as a single jumbo doing the NY to LAX route an there are near 50 of them a day

 

[wrldtvlr]

Because of idiot emission laws mower engines are jetted way too lean.

It's not just carbs. The bloody stupid gas cans that take a three armed contortionist to pour are equally as bad. I love the guys selling water can nozzels that just happen t fit gas cans.

 

[you tube mechanic]

Test of primer bulb results: cold start- 3 x push on primer bulb + 4 pulls on the rope = starts right up. Run for 10 minutes, shut off and let 5 minutes pass to simulate time to dump grass catcher. Hot start- 35 pulls on rope and at pulls 12,15 and 21 back fired through carb and popped pretty loud, after 35 pulls sputtered a bit and died. 3 x push on primer bulb + 4 pulls on the rope, started right up. Repeated 10 minute engine run and shut off, waited 5 minutes. Pulled 5 time on rope, no start. 3 x push on primer bulb + 3 pulls on rope, started right up. Looks like the bulb is the issue and I am going out to get one. Removed bulb and I don't see any obvious defects but will post again if a new bulb fixes the issue. Thanks for everyone's help, even the ones who busted me out for being a YouTube Master Mechanic, LOL.
Say what you like, but Youtube and Forums have saved me a lot of money as usually there is someone out there that has seen or done it all. Its all good.

 

[Mower King]

Test of primer bulb results: cold start- 3 x push on primer bulb + 4 pulls on the rope = starts right up. Run for 10 minutes, shut off and let 5 minutes pass to simulate time to dump grass catcher. Hot start- 35 pulls on rope and at pulls 12,15 and 21 back fired through carb and popped pretty loud, after 35 pulls sputtered a bit and died. 3 x push on primer bulb + 4 pulls on the rope, started right up. Repeated 10 minute engine run and shut off, waited 5 minutes. Pulled 5 time on rope, no start. 3 x push on primer bulb + 3 pulls on rope, started right up. Looks like the bulb is the issue and I am going out to get one. Removed bulb and I don't see any obvious defects but will post again if a new bulb fixes the issue. Thanks for everyone's help, even the ones who busted me out for being a YouTube Master Mechanic, LOL.
Say what you like, but Youtube and Forums have saved me a lot of money as usually there is someone out there that has seen or done it all. Its all good.

Alrighty then....that means the primer bulb is working and there is nothing wrong with the bulb, sounds like it primes each time you want it too......so NO NEED to change it!
Some engines need primed every time to start up....especially with no choke assembly!
Even 98% of NEW MOWERS, even HIGH $$$ Mowers (if carbureted), have to be choked to start every time, even after being ran and are hot!

 

[Hammermechanicman]

I love the guys selling water can nozzels that just happen t fit gas cans.

Yeah..............i put those on my water cans. Honest.

 

[you tube mechanic]

ok, just saw Mower Kings post. but I already spent a whopping $4 for the bulb and installed to find out that didn't really fix the underlying issue, but at least I know how to get it started again in hot condition. I couldn't figure how changing a rubber bulb that was not cracked was going to fix the issue but for the cost I was willing to rule that out. So still having a hard to start problem when engine is hot, but if you give it 3 primes then it starts after about 4 pulls. If you don't prime then your pulling for about 30 times and it backfires at least 3-4 times in during the 30 pulls.

 

[Scrubcadet10]

Pull the spark plug out and take note of the color of it around the bottom of it where the electrode is....white? Brown?Black?

 

[you tube mechanic]

Alrighty then....that means the primer bulb is working and there is nothing wrong with the bulb, sounds like it primes each time you want it too......so NO NEED to change it!
Some engines need primed every time to start up....especially with no choke assembly!
Even 98% of NEW MOWERS, even HIGH $$$ Mowers (if carbureted), have to be choked to start every time, even after being ran and are hot!

I do not have any choke on this mower. Carburetor has a priming bulb on the intake, next thing in the carb is the automatic throttle control as see in pictures I posted on 8/29.There is no manual choke auto choke or thermostat to control an automatic choke.

 

[you tube mechanic]

Pull the spark plug out and take note of the color of it around the bottom of it where the electrode is....white? Brown?Black?

Spark plug looked ok, just pulled it out of a hot engine, man that sucker was hot. here is a pic. I have a brand new autolite 3924 that says it crosses to a RC12YC i can install if needed. Electrode looks like a new one.