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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?

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

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.

jp1961 said:

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

Click to expand...

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.

Recheck the exhaust valve gap.

EngineMan said:

Recheck the exhaust valve gap.

Click to expand...

Valves were very loose. Will report on outcome.

civic said:

Valves were very loose. Will report on outcome.

Click to expand...

Didn't work still backfires. Runs great though

Does it have a solenoid valve on the carb

EngineMan said:

Does it have a solenoid valve on the carb

Click to expand...

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.

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

Jeff,

I thought your idea was great and I bought Sea Foam. I let it do its thing and today no backfire. Makes a lot of sense about carbon build up. This mower is about 10 years old and been through 2 floods. I don't mind throwing money at this mower, best mower I have ever bought but I have had lots of maintenance work. I do it all myself some is trial and error others is from other members here like you that give tips. Will report back on this issue. Thank you!

Hello,

You're welcome. Every once in a while, the two brain cells I have left, hold hands and fire an electronic signal in my brain,,,lol.

Regards

Jeff

So far so good, no backfires since cleaning intake with SeaFoam and adding to fuel, must have been carbon deposits.

Hello,

FWIW, G.M. sells a "Top Engine Cleaner", that does a pretty good job of removing carbon deposits.

It was sold in a quart can, back when cars had carburetors, to pour down the throat of the carb, and now as a spray to use in the intake of fuel injected engines.

Available at G.M. dealerships only.

I'd change the oil, maybe a few times, to clean out any gunk the seafoam dissolved.

Regards

Jeff