123 bang on start

[jzidle]

Hi All,
Sometimes, when I try to start my 123, it will crank and then stop cranking with a tractor-shaking bang. After a few of these, it usually starts and runs pretty well.
What is that?
Thank you!!

[jbrewer]

If you're talking about the engine dying, and as it spins down there a loud bang out the exhaust, in my experience that's usually a mixture problem (and in my case it's generally been a too lean mixture).


Has it just recently started doing this?

[jzidle]

It does it from time to time. It isn’t running at the time. It’s during cranking. It’ll crank, crank, crank, bang several times.

[ol'George]

Adjust the timing by setting the point gap by the static method.

[jbrewer]

Originally Posted by ol'George

Adjust the timing by setting the point gap by the static method.

Thought of that too, but didn't know if this is something that just started happening, or has always happened.

Never hurts to set the timing. :-)

[sawdustdad]

That "bang" is compression stopping the cranking process==your ACR (automatic compression release) isn't working. Or isn't working consistently.

[jbrewer]

Any progress on this?

[cadetpwr]

Good chance the ACR part on the cam is worn out or broken, and timing might be off. If the starter/gen is having trouble each revolution getting the engine past TDC then I would be looking at the ACR on the cam shaft. Had this issue on a very high hour 149. If it cranks over fine but has the back kick when it sparks. Then timing is way off and the spark is to soon. A worn plunger and worn cam lobe can affect this to where the "book" settings are not always correct anymore. The old mechanics rule of thumb for setting points on a K series Kohler was the thickness of a match book cover or business card. Thats for initial set up, then you fine tune it from there. A worn ACR will require engine tear down to replace the worn out parts on the cam shaft or a installing a good used cam. IF you have to do this, do not forget to measure the cam shaft end play. Failure to properly shim the cam for end to end play allows it to slap back and forth in the block when it runs and that creates the common "Kohler Knock" we hear on many older engines in the mid RPM range.

[ol'George]

Originally Posted by cadetpwr

Good chance the ACR part on the cam is worn out or broken, and timing might be off. If the starter/gen is having trouble each revolution getting the engine past TDC then I would be looking at the ACR on the cam shaft. Had this issue on a very high hour 149. If it cranks over fine but has the back kick when it sparks. Then timing is way off and the spark is to soon. A worn plunger and worn cam lobe can affect this to where the "book" settings are not always correct anymore. The old mechanics rule of thumb for setting points on a K series Kohler was the thickness of a match book cover or business card. Thats for initial set up, then you fine tune it from there. A worn ACR will require engine tear down to replace the worn out parts on the cam shaft or a installing a good used cam. IF you have to do this, do not forget to measure the cam shaft end play. Failure to properly shim the cam for end to end play allows it to slap back and forth in the block when it runs and that creates the common "Kohler Knock" we hear on many older engines in the mid RPM range.

Read my post #4
No need to fool with matches or feeler gauges, do it right the first time and
then the timing is set correctly, if the problem is still present check the other things mentioned.