Export thread

Engine runs rough and backfires under throttle

#1

B

bugbug98

Hi. My Ryobi mower (Kohler Courage 19 hp) runs really rough and sputters/backfires hard under load. First season doing this. Cleaned the carb 2x, new air filter, plug, and the gas is new. Fuel solenoid seems fine. Fuel supply seems fine. What's weird is I thought I had the problem fixed (after the 2nd carb cleaning) but during mowing, after about 30 minutes of use, I turned a corner under normal mowing conditions and the problem immediately returned as if a switch had been thrown. Now the engine also runs rough/sputters/surges under all throttle settings. I get a little oil in the exhaust at startup (been that way for a couple seasons). Other than that, the mower has runs fine for 5+ years. Any help would be appreciated. Thanks for your time.


#2

B

bertsmobile1

Remove the fuel tank & clean it out.
Most likely crud in the tank blocking off the fuel line.


#3

B

bugbug98

Ok I will give that a try - thanks. I do recall the fuel filter looked full of gas, and when I cleaned the carb, the leakage of gas from the line when I removed it was appreciable, so I am guessing the fuel supply is fine. Nevertheless I will do as you suggest. Thanks for your time in replying.


#4

M

motoman

Could also be valve clearances changing the timing a hair. Or did you hit something shearing the fly wheel taper key, also moving the timing. My Intek protests when its valve lash is off.


#5

B

bugbug98

Hi - thanks for the suggestion. I don't think I hit anything. It just started acting like this at first startup this season.


#6

B

bertsmobile1

A first start up problem is generally corrosion, fuel deposits, dirt , rodents or insects.

You seem to have the first 3 covered so whip the top cover off and check the line to the coil had not become a mousy teething ring and a bit harder the exhaust has not become bug Hilton.

The last and least common is a sticking valve


#7

B

bugbug98

Excellent - thank you. I will try that.


#8

B

bugbug98

Ok - update - the fuel supply is fine. No blockages. The wires are all intact - no damage from mice. Exhaust is free flowing. Ran fine for 10 min tonight and was mowing, and then an imaginary switch went off and it started sputtering and jerking. Took the fuel solenoid stopper off (to take it out of the mix) and that didn't change anything. Still running horribly. Not sure what else to do. Thanks for everyone's help.


#9

M

Mikel1

Just a thought but is the spark weakening when this happens?


#10

B

bugbug98

Mikel1 said:
Just a thought but is the spark weakening when this happens?
Click to expand...

Hmm. Not sure. I don't get that impression. How would I check?


#11

M

Mikel1

An inline spark tester would be ideal or you can check with another known good spark plug.


#12

M

motoman

Visuals are difficult according to an electrical guru on line because the hottest sparks are almost invisible. Try holding a piece of paper back of the removed plug for highlights. Don't know if 10 minutes gets you to operating temp . Unfortunately transistorized spark modules cannot stand over about 250F. Then the little guys fail although they may work at cold for a while. Sometimes you can actually cool them after they stop and they will again work for a while. Manufacturers know this and heat sink the modules by location. But IMO severe heat as in low/no oil, fan clogged will fry 'em.


#13

B

bertsmobile1

I use a colour tune in these circumstances, excellent piece of kit and at $ 30 cheap as chips. allows you to look into the cylinder and check for lack of spark or lean burn conditions.'Failing that an inline tester works well if the engine will actually slputter to a stop.
If you see flashes and get not bangs to go with them it is a fuel problem ( valves, timing etc )
If you see no flashes as the motors winds down then the ignition is the problem.
Considering the price of the ignition modules, cheap as chips.


#14

M

mwrman

Have you taken the blower housing off? Check the spark plug wires. Also check the valves


#15

J

jspringky

I have the same problem- Kohler SV715 courage 22 hp that I've had for 5 years. First issue ever. Runs great and then after about 10-15 minutes starts running rough with occasional backfire especially under heavy load. Mice had chewed wiring to cylinder #2 spark plug/ignition module. Replaced wiring harness and ignition modules on both cylinders. Also replaced fuel filter and pump. Engine really came to life and could mow for a while, but now back to original problem. Discovered sloinoid was not clicking when turning key to first position. Rebuilt carburetor and solinoid works. However, problem remains. I can get it to run, albeit erratic, by playing with the throttle- moving it into choke mode for a brief time and then back to running mode. One thing to note, I did not realize that cylinder 2 was messed up because of mouse issue- so basically cylinder #1 was carrying the load.

Any feedback is greatly appreciated. Thanks...


#16

M

mbed

jspringky said:
I have the same problem- Kohler SV715 courage 22 hp that I've had for 5 years. First issue ever. Runs great and then after about 10-15 minutes starts running rough with occasional backfire especially under heavy load. Mice had chewed wiring to cylinder #2 spark plug/ignition module. Replaced wiring harness and ignition modules on both cylinders. Also replaced fuel filter and pump. Engine really came to life and could mow for a while, but now back to original problem. Discovered sloinoid was not clicking when turning key to first position. Rebuilt carburetor and solinoid works. However, problem remains. I can get it to run, albeit erratic, by playing with the throttle- moving it into choke mode for a brief time and then back to running mode. One thing to note, I did not realize that cylinder 2 was messed up because of mouse issue- so basically cylinder #1 was carrying the load.

Any feedback is greatly appreciated. Thanks...
Click to expand...

Other thing to check is that fuel tank vent hole (tiny hole on cap) is working. It sounds like as the mower runs and gas leaves the tank, air is not replacing the volume and creating a vacuum which then limits the flow of fuel after that. Once the issue starts, try loosening the fuel cap a bit and see if it stops...hope this helps someone!


#17

Fish

Fish

Unplug one of the plug wires and try to start, then try it the other way.
Tell us what you find.


Footer Links 1

Top