mower difficult to start after emptying the bag

[pbenson23]

I have a Scott mower with a Briggs and Stratton Intek OHV 6.5 HP engine. It starts fine. However, after emptying the bag, I can't start it. Usually, I have to wait for some time, not sure how long but I typically wait for an hour. Then, I can start it again.

What is the cause of the problem and how can it be solved?

 

[slomo]

Fuel tank cap vent bad possibly. Grass, dirt and bugs IN the tank. Choke not working proper. Plugged air filter. Spark plug burried with deposits.

Clean some engine cooling fins when you are at it. See below that red text?

 

[sgkent]

I would suspect it is either the coil if no spark, or if there is a spark then the carb is spilling some fuel, choke closing, either making it too rich to start. Dirty air cleaner could do it too. Do make sure all the cooling fins are clean and that the cooling system is working right. If the engine overheats then it could cause fuel to boil in the carb and dump into the engine making it too rich. Check the oil to be sure it is clean, the correct level AND does not smell like gasoline.

 

[Haligan3]

What "sgkent" said above.....
What you are experiencing is vapor lock. The longer you take to remove and reinstall the bag with the engine off, the more likely you will experience vapor lock. If you kill the engine and immediately try to restart it, it will probably crank. Let it sit without airflow and the cooling effect of fuel flow vaporizing thru the carb due to the engine being off, the carb will get hot. Spray some ice water onto the carb bowl and it will start without having to wait for the carb to cool. If it is a push lawn mower: remove the bag, raise the front of the mower by pushing down on the handle bar all the way to the ground and let it rest there. That will give you easy access for spraying cold water onto the carb bowl. Make sure to keep the air filter dry

It is associated primarily with: mowing a heavy grass load, cooling fins being dirty or air blockage to the cooling fins.
Switching to a full synthetic oil (after it is broke in) seems to help the engine run cooler also.

Let us know if that helps.

I'm not a mechanic but when you farm and ranch, you are forced to become one.

 

[slomo]

Never seen a mower vapor lock. Especially this time of year with cooler temps.

 

[Haligan3]

Mr. slomo, I agree with cooler temperatures lowering the possibility of vapor lock.
I can make a "brand new" DR Trimmer vapor lock(close to 10 years old now), all related to it's workload around my barns and fences.

Quoting from my comment in post #4 relating to vapor lock as a strong likelihood:
"It is associated primarily with: mowing a heavy grass load, cooling fins being dirty or air blockage to the cooling fins."

Quoting pbenson23 from Post #1: "Usually, I have to wait for some time, not sure how long but I typically wait for an hour. Then, I can start it again."
The carb bowl was probably heating up after a few minutes sitting next to a hot air cooled engine radiating heat in still air.
An hour later, the gasoline filled carb bowl was probably much cooler to the touch allowing the vapor lock to dissipate.

Mr. pbenson23, if your mower fails to start again under similar conditions, touch the carb bowl to see if it feels hot to touch. The carb bowl needs to be near the same temperature that it was when you first killed the engine to be able to restart it again.

My take on Adding Engine Heat to a gasoline filled carb bowl.......And my leaning towards Vapor Lock as the culprite for a delayed engine restart.

The carb will absorb heat due to it's close proximity to a hot engine. As long as the engine is running, the engine is being cooled by hopefully adequate air flow that is carrying heat away from the engine. The gasoline filled carb bowl may be less than an inch away from a hot engine. If the fuel bowl is hot, it is a prime candidate for vapor lock. Give a vapor locked engine and carb time to cool, it will start AGAIN if there are no other issues.

While mowing heavy grass, "the governor / air flow vane" maintains engine rpm in a heavy load environment which makes the engine do more work along with producing additional HEAT.
Engine heat is also increased by cooling fins that are dirty or air blockage to the cooling fins.
A lean running engine also produces more heat but I would look at load and air flow first.

As I stated earlier, I farm and ranch.
I'm not a mechanic but I am always trying to bring life back to my equipment from chainsaws to bull dozers.

 

[slomo]

Mr. slomo, I agree with cooler temperatures lowering the possibility of vapor lock.
I can make a "brand new" DR Trimmer vapor lock(close to 10 years old now), all related to it's workload around my barns and fences.

Clean the cooling fins then. It's in every small engine manual known to man as a yearly to-do. Something is causing "your" engine to get hot. Either you have a couple cooling blades broken off the flywheel or something cooling related. A heat related posting topic like this is rare on this board. A 10 year old trimmer will have some grunge around the block.

 

[Haligan3]

It is what it is. Edit/addition: In my opinion, I believe what Mr pbenson23 experienced was Vapor Lock.
I hope we have answered Mr pbenson23 question.

Edit/addition:
Working With What Was Presented:
If the --"engine had died while mowing" -- and not killed by the operator, I would suspect it coil related.
Nothing was noted of a misfire or erratic running prior to being killed by the operator or when it was restarted by the operator.
After restarting, it apparently runs fine (coil working as designed) and to the point as it should that the operator --- deliberately --- kills the engine.
:
Why I Ruled Out The Coil
Coil: It is distinct that pbenson23 ---deliberately--- killed the engine, it was not a coil malfunction that caused the engine to die........
An operating coil should not change status because the "operator killed the engine" (operator stopped electrical flow to the coil).
Coils do not generate heat when electrical flow is "stopped" by the operator nor absorb heat due to not being in close proximity of cooling fins or exhaust.
:
Why I Ruled Out A Non-Venting Fuel Cap
Fuel cap: It apparently was operating as designed up to the moment the "operator killed the engine".
:
If the carb bowl is cooled with a spray of water and it then cranks, suspect "vapor lock"(gasoline vaporizing due to heat when the engine is not running).
A metal carb and bowl absorbs engine heat quickly without the cooling fuel vaporization and airflow of a running engine.
Analogy: A car without airconditioning -"fuel vaporization" or 4 windows open at 70 mph -"airflow of a running engine"; a metal carb / bowl can get hot.
The intake side of an aircooled engine under "normal load" is about 250 deg F but with poor airflow or increased load, expect closer to 300 deg F.
Jerry Toman: Former Heavy Oil Refining Engineer, MS in Chemical Engineering, Massachusetts Institute of Technology
https://www.quora.com/Does-gasoline-have-a-lower-boiling-point-than-water
The lightest components of gasoline begins to boil from 120 - 140 deg F.




Edit/addition:
I think Mr slomo responded to an event that I noted that was 10 years ago when it was a "Brand New" machine.
I am still using the same machine to this day, 10 years later.
What sgkent said post #3 and "If the engine overheats then it could cause fuel to boil in the carb and dump into the engine making it too rich."
Honor your replies with as many replies that may be helpful to the creator of this thread (Mr pbenson23) and the question he posted.

 

[peteco]

Every engine in good conditions starts any time. Did you check spark and coil.

 

[slomo]

If a carb, on a Briggs engined push mower, is getting hot enough to percolate fuel, inside the carb, then that engine block is massively overheating. Think about it.

Not much heat transfers into the fuel tank in a push mower. Same for the rubber fuel line. Next is the engine mounted carb. Could get some heat there from the carb mounting screws and carb gasket.

Never seen boiling fuel inside a push mower fuel tank.

This post came in on Sep 24. Ambient temp at the OP's house "should be" below 80 degrees F. I have no clue what that temp is. Vapor lock is a stretch.

More likely a non venting fuel cap or a flaky ignition coil.