1980 C-145 engine issue

[sb289 0]

After using my C-145 for a while at full  throttle the engine will start to bog down and start jerking back and forth. I have replaced the gas tank valve all hoses

fuel filter and carb. I also installed a new electric fuel pump and the air filter. I also installed a new spark plug.. If I run this at half to three fourths throttle it runs fine.

When it starts to jerk if you can throttle it down fast enough it will not die and when it does it will restart with the same issue but will clear up.

 Thanks for any help, Rob

[wheelhorseman 3,197]

Sounds like a coil or condenser.

[slammer302 2,154]

I had a condenser go bad it it would make the mower sound like it was running out of gas.

I had a condenser go bad it it would make the mower sound like it was running out of gas. Sorry about the repeat.

Edited May 28, 2017 by slammer302

[6bg6ga 271]

Is this a ignition with a separate coil? I looked up the Kohler engine and depending on the year it will dictate the ignition type. It could be a point type ignition system as well as a mag or a solid state ignition system. It could also be a conversion.

 

Points type ignition check the point gap and make sure its set correctly and the points aren't pitted. Checking the cap.... Its very rare but not impossible the cap could be shorting intermittently. Generally caps are either good or they short. This is where it would be nice if included among your test gear is a specially made capacitor with alligator clips that you could simply clip on after taking one lead off of your original cap. Off hand I don't know the value of the points type capacitor. Simply remember if you have a cap that is too large in value you can add another in series and lower the cap value. Example 2)  1 mfd caps in series would yield a .5 mfd cap and two .5  caps paralleled  will  yield a 1 mfd cap. Putting in something close in value is better than taking the cap out to see if it runs.

 

The cap is the easiest and cheapest test so as mentioned it should be done first. So, check the cap first and if the results don't change then try another coil. Also is the voltage feeding the coil what it is supposed to be? Check to see if there is a ballast resistor in the circuit or if the coil includes an internal coil. If so equipped with a ballast check the resistance of it and make sure its not changing with the temp change. This is a voltage dropping resistor and it generates heat also. So in checking put your meter on the VDC scale with negative probe to ground and positive lead on the output of the ballast and again IF ITS SO EQUIPPED. Run the engine and monitor the voltage off the ballast and look for a change and if anything major then change.

 

One thing to keep in mind when troubleshooting is the age of the machine. Also, how long have you owned it? If you bought it used its very possible that there have been undocumented changes by back yard mechanics and some of these changes could be possible changing the coil to the wrong type, inserting a ballast when the coil already internally drops the voltage or a combination of the wrong coil coupled with a ballast. 

[953 nut 51,646]

There could be some junk (hardened fuel residue) in the fuel tank that migrates to the tank outlet and blocks it.        

It may be the condenser or oxidation on the points. Your engine will run just fine (for testing) without a condenser, just unhook the wire to test this theory, To clean oxidation from the points just remove the cover and fold a small piece of 600 sandpaper (abrasive side out), put it between the contacts and pull it through.

[6bg6ga 271]

I'll add onto what has been said above. First a different condenser is always better than unhooking the original. Running the ignition without points even for a short time contributes to pitting of the points. I know its anal for me to say that but in the past I spent too many hours with dual point racing type ignition systems on engines like the Ford 406cu in 405 HP engine. Habit still tells me its a no no to run without a condenser.  

 

Secondly when done with the 600 grit paper run a clean piece of newspaper thru the points to clean them. Run a strip of paper thru them until the paper comes out clean.

For the record, "condenser" is an age old term, and "capacitor" is a newer term for the same device.  Ignition capacitors are still commonly called condensers.

Many people will replace a condenser with regular periodic maintenance, just because they have no way to tell how much longer it might last. But some new condensers might be bad right out of the box, or might fail very shortly after installation. My approach is to carry a known good condenser in the tool kit, and don't replace the old one until it fails.  How to test.
1.) Remove the condenser from the engine (or at least disconnect the lead wire). Note the small metal connector located on the end of the condenser. This connector is the "hot" or power connection. The metal case of the condenser is the grounding point. Discharge the condenser by shorting the lead wire to the case.

2.) Switch the meter to the ohms position. Place the red lead into the "ohm" connector on the meter. Insert the black lead into the "com" or common connector on the meter. Set the resistance range to the highest available setting (if it is selectable). Connect the test leads together and zero the meter. If the meter won't zero replace the battery. (Yes, an ohm meter has a battery).

3.) Touch the red lead to the hot connector on the condenser. Place the black lead to the metal case on the condenser. The meter's needle should jump slightly to the right (toward 0-ohms), then should drop back to the left towards infinite resistance). Hold the leads in place for 15 to 20 seconds. This action places charge in the condenser. If the test shows any reading other than infinity, the condenser is leaking and needs to be replaced.

4.) Remove the leads and reverse the placement to the condenser. Move the red lead from the hot connector to the metal case, and move the black lead from the metal case to the hot connector. At the moment where both leads are touching the correct points, the meter should jump towards the right. The second time the needle may move twice as far, as this action discharges the condenser. Holding the leads in contact should again result in movement of the needle back toward infinite resistance.

5.) Movement of the meter's needle indicates the condenser is good. If no movement was indicated on the meter in any circumstance, the condenser is bad and must be replaced. Retest the condenser several times for a consistent reading.

In operation the condenser will "ring" at up to 300 volts, so the condenser needs to be rated much higher, no less than 600 volts DC. The ignition will likely work with any capacitance value between 0.05 and 0.6 microfarad. Too high or too low value may eventually transfer metal from one side of the contact points to the other side leaving a pit and a point. Capacity of capacitors ranges from 0.1 microfarad to 0.33 microfarad.

A capacitor may absorb moisture over a long period of time, and moisture can cause failure of the condenser. So it is possible that a condenser stored for 10 years or so might be bad or might fail prematurely in service. It is a good idea to check your spare condenser occasionally. 

 

If  you have a newer meter with a cap test feature simply move your selector to the cap test function and test. If it tests open or short simply throw it away. If it tests a different value than its supposed to be it will make a good test cap.

  Edited May 28, 2017 by 6bg6ga

[6bg6ga 271]

A simple capacitor like the one in the picture will/can serve as a nice test cap. A rating of at least 600 volts and better yet 1000 volts will insure a very long life. Actually this type of cap with heat shrink and terminals on the ends will provide a very long life with no problems ever of moisture causing problems.  Cost is about $5

[tunahead72 2,337]

On ‎5‎/‎27‎/‎2017 at 8:06 PM, sb289 said:

After using my C-145 for a while at full  throttle the engine will start to bog down and start jerking back and forth... If I run this at half to three fourths throttle it runs fine.

When it starts to jerk if you can throttle it down fast enough it will not die and when it does it will restart with the same issue but will clear up...

 

I'm not sure I understand what this means.  Do you mean the engine itself is moving back and forth on the rubber mounts and cradle, or something else?