Engine surging, dies at low throttle

[bbingham]

As the title says, the engine-Kohler 18hp on my 2000 model year 3184 is surging and then dying at low idle when it warms up after a few minutes. I previously changed the plugs (gapped correctly), engine oil/filter, tranny oil/filter, air filter and the in line fuel filter. spark plug wires are fine, cooling fins are clear/clean, the engine looks brand new in fact. Any ideas what I may have done to cause this to occur now? Used only CC parts from the dealer per specs. Just in need of a minor carb adjustment maybe? Not sure if it is running hot since I dont have any history with this tractor - can feel the heat coming from the front as I drive it after awhile - hood gets hot - normal? I just got it a couple of weeks ago. Only 157 hrs on it when bought used from the dealer and ran okay before I did my maintenance. Also, appears to lose some power/speed too after awhile and backfired once on me when shutting the tractor off.

Very slow in reverse, is that normal too?

Thanks for the help.

 

[agitch]

Could be carb adjustments are out. And, if it's overheating that could be caused by the carb adjustment being too lean if it's an adjustable carb.

 

[bbingham]

Still having issues with the engine surging (worse when it's still cold - doesnt seem to surge as much after it warms up a bit) and loading up/backfiring when shutting down sometimes. Almost sounds like the engine is continuously/rapidly backfiring when at high rpm/full throttle - choke is off. I only see one adjusting screw on the carb for idle - is the second screw for mixture hidden under a lead cap on the carb somewhere? I am hoping to get through the winter and then take it into the shop for repair/adjustment this spring. Any help would be appreciated.
Thanks

 

[agitch]

That carb may not be adjustable. Since it ran okay before you did the maintenance it shouldn't be something too major. I know backfiring is bad for the engine. I wouldn't wait til spring to have the dealer look at it. Did you put in crappy old fuel?

 

[bbingham]

No, new fuel and plugs and fuel filter. Could it be the idle adjustment is still off on the carb and would cause the problem - maybe I am just not setting up the idle correctly? I dont believe the mixture is adjustable on this model carb either. Would too light an oil viscocity possibly be a cause? Maybe I should pull the plugs again and re-check the gap, they are the correct plugs - I bought them at the cub dealer - hope they gave me the correct ones. I cant think of anything else that would cause the engine surging and sporadic backfire when turning off the engine. I looked at the Kohler site and they had something in there faqs section about leaving the throttle at half speed when shutting down to prevent backfires. Thanks for trying to help me out - appreciate it.

 

[mbounds]

Bill B:

1) Adjust the idle needle according to your manual or the one you download from the Kohler website.

2) A Cub Cadet Service bulletin on the backfiring problem says: to solve the problem, you set the throttle to the 3/4 position and then turn off the ignition. The "tree huggers" strike again.

2) Your surging problem is often the result of fuel starvation to the carb....You said that you changed the fuel filter?? I'd take a real good look at that. Put it in backwards, or wrong type filter?? Look for a restricted fuel flow. The surging is likely caused by insufficient fuel flow and the the governor goosing it trying to keep the engine running at the correct operating rpm.

Myron B

 

[bbingham]

Thanks Myron, I looked at the fuel filter and it is installed in the correct direction and should be the right part since I got it at the cub dealer - never know though. Can air get caught in the fuel line at the filter and cause the starving issue or would the fuel pump prevent that? The surging becomes less noticeable after the engine warms up - still an idle adjustment issue? I will re-adjust the carb per the instructions again and see if there is any difference, maybe I didnt wait long enough the last time I did it to ensure the engine was warmed up enough so the calibration is off.
Thanks

 

[agitch]

Myron brought up an excellent point if it started running bad after you did your maintenance to it, it must be something related to that. Is the air filter installed correctly? Sure does sound fuel related like he said. Is it good fuel straight from the gas station or has it been sitting in a gas can for awhile? Is the fuel filter identical to the one that was on it? Maybe some dirt/gunk got in the carb and it's restricting fuel/air flow. You may want to pull the carb and soak it and clean it real good. Hope you can figure it out!

 

[dcurran]

That also brings up another good point. Is the screen in the gas tank clogged? Lines? Pepcock?

 

[takers]

Bill,
Does the surge go away if you partially choke the engine? If so, It's too lean. Check for loose carburetor mounting bolts. Also, make sure you run the green prefilter on the air filter and it is lightly oiled. These engines are factory set to run as lean as possible. The lightly oiled prefilter causes just enough air restriction to allow the engine to run richer eliminating the lean surge.
Terry

 

[bbingham]

Hey Terry,
I checked the carb and it feels secure, the green sponge pre-filter is on the air filter and is lightly oiled - I may re-oil it up a little. I am going to reset the carb idle screw per the manuf instructions and see if it makes a difference. I may not have waited long enough the first time for the engine to warm up. I verified the fuel filter is installed in the right direction - question though - should the fuel filter be totally full of fuel (both sides) or should it be only 1/3rd full on the tank/inlet side - which mine is. Is it possible the fuel pump is sucking in air at the fuel filter hoses - starving the carb? Thankfully the temps here in upstate NY are going to be in the high 40's to almost 60 for the next couple of days - excellent time for me to hopefully correct this problem before the lake effect snow finally hits us! The gas I used is a couple of months old - same gas for the mowing too. I buy 10-gals at a time to ensure I never run out during one of our blizzards here. I dont believe it is stale gas - the surging eventually subsides and she runs pretty normal after a a period - bad gas would make the engine always run poorly.
Thanks for the help/ideas.
Bill

 

[bbingham]

Terry, I forgot to answer your question - yes, the surging does subside if I partially choke the engine while it is still cold, and when fully warmed up surging goes away unchoked.
Bill

 

[mgonitzke]

Bill-

With the gas being two months old, you're close to being on borrowed time with it. Today's gas is really crappy, and any more than a month old and stuff starts running weird. I had a CC 108 that has gas in it that was 2-3 months old that started really hard and would only run at above 3/4 throttle and I'd have to pull the choke every time it tried to die. After it warmed up it was fine.

 

[bbingham]

Okay............. I re-set the carb idle adjustment per the manual and sprayed the linkage/control arms pivot points and springs/etc... with brakeklean to remove grime and crud that was causing some sticking and then sprayed everything with a white grease - working the linkages as I sprayed. After doing all this it is now running like a champ again. I dont own a tach so am going with what feels and sounds about right for low idle - guessing. Running smooth even at low idle with the blower engaged and moving forward. Probably need to make an additional adjustment on the throttle linkage because there is alot of play at low throttle before the engine starts to rev up as you move the throttle knob/lever up. More turtle than rabbit until at least half way up the scale. I appreciate everyones advice and help on here, thanks again.
Bill

 

[kide]

It could have been linkage binding - that will cause them to over-rev, as what usually happens is that it's only binding in a certain portion of it's movement - it takes more force from the governor to move it through the binding zone, once it's free, the governor now pushes it too far, then snaps closed because it's running too fast, then starts all over again. Your cleaning and lubing probably fixed it..

 

[agitch]

If you keep gas in a gas can for more than a few weeks use something like fuel Sta-bil in the can. That's what i use and it seems to do the job.