Backfire when hot only

civic

Active Member
Joined
Oct 31, 2016
Threads
1
Messages
94
I have a Honda mower HRR216VKA that starts cold fine and runs fine, but when I shut off and restart a minute later it will backfire and then runs. Any ideas?
 

jp1961

Well-Known Member
Joined
Jul 22, 2013
Threads
39
Messages
785
Hello,

My Chilton's guide to small engine repair lists these causes for backfires.

!. The carb is adjusted too lean. (Is the air filter relative clean?)
2. Ignition is not timed correctly. (Spark plug look OK?)
3. The valves are sticking. (Have the valve lash ever been adjusted?)

Regards

Jeff
 

tom3

Lawn Addict
Joined
Apr 9, 2018
Threads
25
Messages
1,579
Somewhat normal for some mower engines I think. When you shut it off, the engine pulls fuel/air until while it is winding down, maybe has a easy start exhaust valve opening at low rpm too. This residual fuel in the exhaust and muffler ignites and causes the backfire I guess. Some mower engines have a solenoid valve on the carb that shuts off the fuel flow when the switch is shut off, shouldn't backfire if so. Might try idling the engine down before shutting off.
 

civic

Active Member
Joined
Oct 31, 2016
Threads
1
Messages
94
Hello,

My Chilton's guide to small engine repair lists these causes for backfires.

!. The carb is adjusted too lean. (Is the air filter relative clean?)
2. Ignition is not timed correctly. (Spark plug look OK?)
3. The valves are sticking. (Have the valve lash ever been adjusted?)

Regards

Jeff

Air filter is new
Spark plug is new
I adjusted valves about a year ago, this I may check again.

It is a little weird when this happens. I pull the cord, backfire, and then it starts all in one pull and only when it is hot.
 

EngineMan

Lawn Addict
Joined
Jun 12, 2012
Threads
9
Messages
2,275
Does it have a solenoid valve on the carb
 

civic

Active Member
Joined
Oct 31, 2016
Threads
1
Messages
94
Does it have a solenoid valve on the carb

It has an auto choke wax cylinder that has never been replaced and there is a TSB on hard starting for this mower. This mower starts in one pull cold or hot except I get one backfire when hot.
 

jp1961

Well-Known Member
Joined
Jul 22, 2013
Threads
39
Messages
785
I'm wondering if carbon buildup is causing the backfire when hot situation.

It's possible the carbon is staying hot enough to partially ignite the fuel before the spark plug does?

Regards

Jeff
 
Top