GT1800 backfire

[Wayne0 453]

1984 GT1800 Work Horse (Ol' Rusty) has backfired on shutdown since I've owned it. 30+ years. I'd say 80% of the time. Out the exhaust. Ideas?

[wallfish 16,994]

Try shutting it down with the throttle wide open full

I know this sounds counterintuitive but it worked for me

[Wayne0 453]

Sounds bass ackwards, but I'll try it.

[c-series don 8,687]

I’ve had a GT-1800 since new, I always let it run at an idle for at least 30 seconds before shutting it down.Actually I do this with most of my tractors. Does yours have the factory muffler? 

[Wayne0 453]

12 hours ago, c-series don said:

I’ve had a GT-1800 since new, I always let it run at an idle for at least 30 seconds before shutting it down.Actually I do this with most of my tractors. Does yours have the factory muffler? 

Not original, but genuine B&S replacement. Original did the same.

Edited August 7 by Wayne0

[cleat 5,915]

My Briggs single in a 17-44HXL did the same.

I would idle it down for a bit then shut it down and at least half of the time there was a bang.

It got so that i would idle it down then get off the machine and reach over and shut the key off as I then quickly got away as the backfire would be quite loud.

Must be a Briggs thing as none of my other tractors do this.

 

[Fordiesel69 263]

Our GT1642 does this too.  The key is to idle down and wait 1 minute before shuttiing off.  That's all it takes.

 

[pfrederi 17,700]

I have some K series that will do that if they have been run hard and shut off right away ...so does my 4 Cylinder 1951 Case VAC

[Bill D 1,916]

Try running some Seafoam thru it to clean some of the carbon from the cylinders.  Then adjust the main jet to make it run a little richer.  My dad's 312-8 did this until I set the carb a bit richer.

[c-series don 8,687]

 @Bill D If I remember correctly there’s no high speed adjustment on those engines? Or maybe it was just no low speed? Whatever it is it’s not a simple an adjusting a K-Series Kohler, that I do know. I’ve ran my Work Horse with the choke slightly out for years even after a thorough cleaning of the carburetor. 

[Wayne0 453]

I broke the throttle cable the other day and had to shorten it a couple inches to repair. Since then, the low end idle has been lower/slower. So far, it has not back fired! Seems the idle was too high at shut down?

Edited August 31 by Wayne0

[ebinmaine 67,401]

5 minutes ago, Wayne0 said:

I broke the throttle cable the other day and had to shorten it a couple inches to repair. Since then, the low end idle has been lower/slower. So far, it has not back fired! Seems the idle was too high at shut down?

 

That's a thing. 

 

Oddly enough,  if you shut down an engine at FULL throttle it won't backfire though.....

[Handy Don 12,206]

56 minutes ago, Wayne0 said:

I broke the throttle cable the other day and had to shorten it a couple inches to repair. Since then, the low end idle has been lower/slower. So far, it has not back fired! Seems the idle was too high at shut down?

The thing it took me a while to “grok” is that the carb, piston, valves, and muffler are totally unaware that we’ve shut off the spark (except on the newer engines that have the solenoid fuel cutoff at the carb). Air is still being pulled in, mixed with fuel, compressed, and exhausted.

If the muffler is hot enough to ignite that exhausted fuel/air mixture, it’ll backfire.

For engines I use only sporadically, I close the fuel petcock and let the engine run until fuel starvation shuts it down. Lessens the chance of mess in the carb from fuel evaporation and for sure no backfires!

[ebinmaine 67,401]

32 minutes ago, Handy Don said:

The thing it took me a while to “grok” is that the carb, piston, valves, and muffler are totally unaware that we’ve shut off the spark (except on the newer engines that have the solenoid fuel cutoff at the carb). Air is still being pulled in, mixed with fuel, compressed, and exhausted.

If the muffler is hot enough to ignite that exhausted fuel/air mixture, it’ll backfire.

For engines I use only sporadically, I close the fuel petcock and let the engine run until fuel starvation shuts it down. Lessens the chance of mess in the carb from fuel evaporation and for sure no backfires!

 

 

 

And yet... when I do that on my Kohler Magnum 16 or the Tecumseh OHV160...

They'll BOTH backfire.  

One loud POP at the end of all movement.  

 

[gwest_ca-(File Mod) 11,040]

Wonder if the governor is going to wide open throttle after the ignition is OFF and the engine rolls to a stop?

[8ntruck 6,998]

 that is a good thought. 

[ebinmaine 67,401]

1 hour ago, gwest_ca said:

Wonder if the governor is going to wide open throttle after the ignition is OFF and the engine rolls to a stop?

 

5 minutes ago, 8ntruck said:

 that is a good thought. 

 

 

Take this with a grain of salt because I'm not familiar with the mechanics of WHY or how this works. 

 

If I shut off either engine running at WOT or shut off the engine at any rpm and immediately put the throttle lever at WOT it never back fires.