154 random frequent misfire

[Duner]

154 will start at slightly off idle and not miss. Increase RPM and engage mower and misfire starts.
BUT let it warm up for about five minutes and misfire goes away and it runs good.
I had another vehicle that did about the same for misfire but misfire would not go away ,ever.
Replaced the condenser on other vehicle and all was well.
Anyone ever have a condenser act like I described on my 154?

[64/67lo-boy]

Yes thats a very common symptom of a bad condenser.

[64/67lo-boy]

Yes thats a very common symptom of a bad condenser.

That is when it miss fires and miss fire doesn't go away.

[Eugene]

Most likely misfiring one cylinder. Automotive Oscilloscope would easily identify the problem.

Lacking the O-scope, timing light on one plug wire at a time will identify the problem area - which cylinder. Then you will have to diagnose the problem.

[Gary Dotson]

Usually, when I encounter a miss fire like this, it turns out being a spark plug or a bad plug wire. A scope would be very helpful, it’s been a long time since I’ve had mine out. Make sure your plug wires and coil wire are fully inserted in their respective towers, I’ve seen that cause a miss like this.

[Duner]

It acts exactly like a failed condenser would in this respect.
Starts and idles fine. Increase RPM and RPM and load it completely breaks down.
Let it warm up for five minutes and it runs perfect. Been doing this all last mowing season. Thanks for the thoughts.

[Larry B]

If you want to test for a bad condenser just disconnect it. It is only there to extend point life. Running for a short time won't hurt the points. If you disconnect it and the misfire problem goes away then bad condenser.

[Eugene]

If you want to test for a bad condenser just disconnect it. It is only there to extend point life. Running for a short time won't hurt the points. If you disconnect it and the misfire problem goes away then bad condenser.

The condenser does reduce the arcing at the points. But it has other functions such as discharging back into the coil to improve the spark quality.

Without the condenser in the ignition circuit the engine may run, just not very well. Frequently the engine will not run.

The condenser is either good or bad. No in betweens.

[Duner]

I can tell hear if it was one cylinder. It is 2 or more and random ,frequent and sporadic.
I have owned and fixed points ignitions for over 60 years.
If it would not cure itself after 5 minutes I would say condenser.
Thanks for the replies.

[cubbrian]

I had a similar issue when i purchased my 154. It would start and idle perfectly. Give it throttle and it sounded like it was missing/starving for fuel. After many hours of troubleshooting, I found that the coil was bad. Go figure.

[Duner]

I will try a different coil. Thank you. Did yours run better after five minutes or so?
I have had bad condenser that acted like yours.