Backfire when shuttng off.

[springerpete]

Has not done this for quite some time. But today it started doing this again. Not every time. Seems as tho' it like to surprise me. Is there a cure ?

[Tom Wesenberg]

Try turning off the gas and let the carb run low or out of gas.

[Rock Hornbuckle]

I shut the engine off by putting it in gear with my foot on the brake and let the clutch out slowly.

[700rpm]

Originally Posted by Rock Hornbuckle

I shut the engine off by putting it in gear with my foot on the brake and let the clutch out slowly.

I would worry about damage to the clutch disc or pressure plate. Doesn't your key work?

[Mitch//pa]

make sure your not idling to high, also try retarding your spark lever before shutdown

if you have to shutoff your fuel to prevent backfire its masking another issue

[William Kelchner]

Sponsored Links (Register now to hide all advertisements)

I finally adopted what was mentioned above -- close the fuel valve and let it run out of gas - somewhere between 1-2 minutes. No more embarrassing BOOM.

[Patrick L.]

I shut the fuel valve before shut down, push the left lever up and turn off the key. That said, it should shut down without a backfire without going thru any rig-a-ma-roll.

[ba49]

Check and see if the bolts are loose holding the carb to the manifold. I just went through the same thing and the bolts were loose. Also if your running a tilitson carb, make sure it's not warped at the manifold.

[BILL WILLIAMSON]

An occasional shut down POP is great FUN! "WELL, I hear Ol' Bill, back from shopping"!-----Boy! It's hard to get a Dog knap! Buster T.

[dmaxweb]

Condenser

[Duffy1]

Do a search . A lot of info on this subject.

[Tom Wesenberg]

Originally Posted by dmaxweb

Condenser

The ignition, including the condenser, is out of the picture once the key is turned off.

Raw gas hitting a red hot spark could cause a backfire. My Cub Cadet would always wait about 15 seconds after shut down, then give off a shotgun blast. About a year ago it suddenly quit doing that, and I miss it.

[31 A4door]

Tom is correct in my opinion. Sounds like hot plug or carbon causing the problem. Have you ever had the head off to see how much carbon buildup is in there?

[jerry of whidbey]

un burened gas in the manifold running to rich

[SeaSlugs]

Originally Posted by Tom Wesenberg

The ignition, including the condenser, is out of the picture once the key is turned off.

Raw gas hitting a red hot spark could cause a backfire. My Cub Cadet would always wait about 15 seconds after shut down, then give off a shotgun blast. About a year ago it suddenly quit doing that, and I miss it.

oh yea my B&S rider would do that like clockwork if i killed it at anything other than low idle. I got used to lowering the idle all the way down then let it idle slow for about 10-15 sec then shut the key off. Gives the engine some time to cool down.

[OL JENNY]

I had the problem, and if I did not run the gas out it would have the loudest backfire you could imagine. This was very bad if you pulled in to get gas. I finally found a small crack in the exhaust manifold that apparently provided enough heat on the carb that gas fumes would ignite after shutting the engine off. New manifold resulted in solution.

[Purdy Swoft]

Mitch makes a good point in post 5. Its not the gas in the carb that does it, Its letting the engine idle slowly for the length of time that it takes for the gas to be used up that is in the carb and fuel line. Actually, you must have a leak at the exhaust manifold connections or a cracked manifold that allows air to enter the muffler for the backfire to happen. Weak ignition that doesn't burn up all the fuel is a big contributor. Fuel that isn't burned in the combustion chamber collects in the muffler. When the engine is cut off and the flow through exhaust stops, the muffler gets hotter. Air is necessary for ignition and explosion, this is where a leak between the manifold and block or at the exhaust pipe to the manifold comes into play. Running the GAV too far open or a carb running too rich or weak ignition will cause gas to collect in the muffler. Its a pain and embarrasment but it has happened to most of us at one time or another. just my thoughts.

[Rock Hornbuckle]

Originally Posted by 700rpm

I would worry about damage to the clutch disc or pressure plate. Doesn't your key work?

Yes Ray, my key functions.
I should've mentioned that I let the clutch out slowly as I turn off the ignition. I stop the rotation of the engine so it will not continue to suck in gas and pass it out into the hot exhaust causing a backfire.

As a teenager in my '50 Ford business coupe, I would cause backfires while driving, by turning off the key, pressing on the gas pedal, then turning the key back on. It great fun to do it in front of the High School. lol

I know, it's a great way to blow a piston or blow out a muffler. Been there! But it was such fun being a teenager.