312-8 wont run - Need some help

[Jimcamp 2]

Hello everyone, 

 

I am having trouble getting my 312-8 with a Kohler magnum running and need some help please. -The background, for the past couple months she has been difficult to start, I would need to crank for a while to get it going, but once started it would run great. Last week while trying to get it running it stopped cranking. Hit the key again and heard one clicking noise, did this a couple more times with the same result. At that point I checked the battery which read at 12.5. I checked the started solenoid with a testlight and found I had power coming to the solenoid but not coming out of it when turning the key. After replacing the starting solenoid, I am again able to crank the engine again but it still will not start. I am getting fuel coming from the fuel pump to the carb, the carb is clean and the float is not stuck. I have good compression and I have spark. Hit it with a little starter fluid, nothing! Why in the world will this darn thing not start? Any ideas or advice is greatly appreciated. 

 

Thank you!

Jimmy 

Edited September 13, 2021 by Jimcamp
Typo

[Pullstart 67,119]

 

I’ve had engines that had spark but wouldn’t start finally run when I replaced the spark plug.  The spark didn’t look a whole lot different to me, but it made a world of difference to the engine!

[Jimcamp 2]

Sorry, failed to mention originally, I picked up a two pack of champion spark plugs, same result with either plug in it. 

[Pullstart 67,119]

Do you have ample compression?  Did you try the ole’ thumb over the spark plug hole test?  I know you said you’ve got fuel at the carb and it’s clear.  After cranking, does the plug get wet?  

[953 nut 60,457]

8 hours ago, Jimcamp said:

The background, for the past couple months she has been difficult to start, I would need to crank for a while to get it going, but once started it would run great.

There could be a problem with the fuel pump or fuel hose allowing gas to run back to the tank. The fuel pump has two small valves in it that keep the gas from backflowing and a slight pinhole in the fuel line could allow this to happen too. After the tractor has been sitting unused for a few days remove the fuel line from the fuel pump at the carburetor and route it to a safe catch can. Now crank the engine over to see how long it takes for gas to come out.

If you are using gas with ethanol please STOP. Ethanol will kill the fuel system, you can find a station that sells real gas at this site, https://www.pure-gas.org/

I would suggest doing a bit of basic maintenance. Replace the fuel line and filter coming from the tank, replace the air filter and install a new spark plug gapped at .025.

[Jimcamp 2]

51 minutes ago, pullstart said:

Do you have ample compression?  Did you try the ole’ thumb over the spark plug hole test?  I know you said you’ve got fuel at the carb and it’s clear.  After cranking, does the plug get wet?  

According to my compression tester, I’m getting just about 100lbs. If I take the plug out after cranking, it is wet with gas.  

[Pullstart 67,119]

1 minute ago, Jimcamp said:

According to my compression tester, I’m getting just about 100lbs. If I take the plug out after cranking, it is wet with gas.  

100 lbs sounds about right, these have ACR systems so while running it’ll but higher.

[Jimcamp 2]

47 minutes ago, 953 nut said:

There could be a problem with the fuel pump or fuel hose allowing gas to run back to the tank. The fuel pump has two small valves in it that keep the gas from backflowing and a slight pinhole in the fuel line could allow this to happen too. After the tractor has been sitting unused for a few days remove the fuel line from the fuel pump at the carburetor and route it to a safe catch can. Now crank the engine over to see how long it takes for gas to come out.

If you are using gas with ethanol please STOP. Ethanol will kill the fuel system, you can find a station that sells real gas at this site, https://www.pure-gas.org/

I would suggest doing a bit of basic maintenance. Replace the fuel line and filter coming from the tank, replace the air filter and install a new spark plug gapped at .025.

Fuel system was my initial thought. But if I undo the hose goin from the pump to the carb and crank it, I get gas flowing out near instantly.  I’m twrms of fuel it self, I luckily have a station near by that sells 92 and that what I run.

[Ed Kennell 42,267]

Pull the plug, ground it and check for spark.     If you have good compression, and fuel, it almost has to be missing spark.

[pfrederi 18,725]

If you plug is wet with gas and you have compression you have a spark problem. Could be a bad wire or defective plug (I stopped using Champion some time ago as they would spark laying on the head but not under compression.) I also have several of teh cheap Harbor Freight neon s[park tester.  They will show a flash but there is not enough juice to fire the elug,  One of these B&S testers will give you a more accurate assessment of you igniton power

[OutdoorEnvy 1,777]

Try cleaning a couple ground locations.  First where the negative battery cable attaches to the tractor.  Clean it with a wire brush and/or sand paper so you have a nice metal surface to attach it to.  Remove any rust and paint in the way.  Second location to do the same is the solenoid ground location.  Remove all paint and rust.  If you have dielectric grease you can put some on the ground spots as well.  Also double check the post on the starter where the positive cable attaches that it is clean and tight.  These three areas have solved most of my voltage issues for the situation you are describing.  It's easy and fairly quick as you can probably do all these in around 10 mins.  Also make sure your battery has a full charge.   

[gwest_ca-(File Mod) 11,540]

Something you can try.

Simply disconnect the wires from the seat switch temporarily for testing purposes.

That should put the seat light on but still enable the ignition to work.

[Bill D 2,287]

Remove the flywheel cover, and check the condition of the spark plug wire.  It may be pinched or cut which can cause it to ground out.  It comes out near the carburetor and the side cover can cut into the insulation and ground the plug wire out.  You can also unplug the rectifier near the the carb, then unplug the 5 pin connector near the starter.  This will isolate the engine electrically from the tractor. Try starting it.  If it starts then there is an electrical problem on the tractor that is preventing it from starting.  To stop the engine with it unplugged from the tractor wiring harness you will have to either choke it out or pull the plug wire off.  Wear rubber gloves.  Hope this helps.