KT17 backfiring

[Bull 33]

Hello All,

 

I own a model 417A with the Kohler KT17series 2 engine (468 hours). It has a lot of power and starts up pretty quickly. When I purchased it I always got a couple of backfires after I shut it down. I have since changed the spark plugs, points, condenser, coil, ignition wires, fuel and air filter.  This was all part of a planned maintenance plan and the backfiring in turn ended for awhile. I have used it quite a bit the last few days but whenever I shut it down it always backfires for just one time. I have to say that I also previously cleaned the carb out with Seafoam but was wondering if anyone had some ideas on the backfiring?

When I replaced the points I saw that they were previously gapped at .014 but I gapped the new one's at .020. The only other thing I seem to notice is sometimes it is hard to start after heavy use. Has anyone set their ignition point's  using a timing light? Any suggestions will be appreciated.

 

Regards,

Bob

 

 

[Handy Don 12,235]

Backfiring is unburned fuel getting into the exhaust system and burning there.

If the engine was backfiring while running, then you'd want to confirm that points, condenser, plug, etc. are working correctly all the time. 

But you are getting the backfire after you turn it off, so NONE of the electrical elements are involved.

The likeliest is that the engine is running lean and as a result the exhaust manifold or muffler is getting excessively hot. When you shut off your motor the carb is still mixing fuel into the air* and the engine is still pumping it through. BUT, with no spark, it goes right out the exhaust. When that fuel/air mix hits the really hot exhaust, it burns as a backfire.

Go to the Kohler manual and adjust the carb according to the sequence they outline.

 

*Many "low emission" carbs from 1996-7 and onward have a solenoid fuel cutoff that stops fuel flow into the carb when you turn off the engine. Since this was near the end of production for WH, very few horses have these engines.

Edited September 21, 2021 by Handy Don

[953 nut 55,307]

9 hours ago, Bull said:

Has anyone set their ignition point's  using a timing light?

Setting your ignition points with a timing light is the most dependable method for accurate points gapping. 

Always idle your engine down as slow as it will go prior to shutting off the ignition. Incorrect ignition timing can cause an engine to run hotter than normal too. This Service Manual should be helpful.

 

[kpinnc 12,087]

I'm guessing you have a cannister muffler, and those cause everything I have to backfire if I shut down- unless I idle down for a few seconds beforehand. 

 

On an older engine without a fuel solenoid in the carb, I don't know of any other way to keep from dumping fuel while the engine spins down. 

 

Not to mention all the carbon buildup in the muffler. That stuff holds alot of heat! Throw a little fuel in there from a mechanical system, and it's like 4th of July....

Edited September 21, 2021 by kpinnc

[lynnmor 7,308]

1 hour ago, 953 nut said:

 

Always idle your engine down as slow as it will go prior to shutting off the ignition.

 

And be sure that the idle mixture is correct and the idle speed is no faster than specified.

[Bill D 1,926]

Set your timing with a timing light.  Also consider rebuilding the carb and check the height setting of the float when you do.   Once you've done those things, run several cans of Seafoam thru it to help clean out any carbon deposits in the cylinders.

Edited September 21, 2021 by Bill D

[oldlineman 1,481]

I always let my tractors idle for a few min. before shutting down to let them cool down a bit. As said above may be running a little lean also.

[Bull 33]

Thanks everyone for your input.

 

Bull

[Bill D 1,926]

14 hours ago, lynnmor said:

And be sure that the idle mixture is correct and the idle speed is no faster than specified.

I have a timing light with a tach on it.  Very handy. 

Also, put the points cover screws back in before you start the engine to time it.  One of the screws is tapped into a pressurized oil passage.  You will spray oil everywhere if you don't.

[lynnmor 7,308]

3 hours ago, Bill D said:

I have a timing light with a tach on it.  Very handy. 

Also, put the points cover screws back in before you start the engine to time it.  One of the screws is tapped into a pressurized oil passage.  You will spray oil everywhere if you don't.

 

The reason that I mentioned idle mixture in this thread is that you could have the mixture way off and then adjust the idle speed to compensate.  That larger throttle opening will contribute to the backfiring problem.