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Have a cub cadet with a 173 cc powermore motor. Cleaned the carb as it would not start, when pulling then it pulled fine. I got the carb cleaned and started it. Did not notice any jerk back and motor ran fine. Shut it off, washed it and then tried to start again. Cord was hard to pull and then didn't start first time. Jerk back, but on second pull, she started and ran fine. About 30 minutes later tried again. Jerk back, but will start eventually and runs like a champ. I checked the flywheel key (twice) and it is perfect. Checked the plug, dry. Rotated the engine with the plug out, no oil or gas came out. Checked the valves, they were good but adjusted again. Put it all back together and still have jerk back on the pull. Starts eventually and runs great. What am I missing on the jerk back?

Does the decompression work?

DunDikke said:

Does the decompression work?

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How would I check that

Is the blade installed?

Check to see if the blade is loose.

Romore said:

Is the blade installed?

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yes, blade installed and tight

Three things cause jerking on most small engines. Loose blade, raw fuel in cylinder, and sheared flywheel key. Time to go back and double check these three things. I’m guessing you may find something wrong with the carb, as that was when the problem started occurring.

I will pull the carb tomorrow

Rivets said:

Three things cause jerking on most small engines. Loose blade, raw fuel in cylinder, and sheared flywheel key. Time to go back and double check these three things. I’m guessing you may find something wrong with the carb, as that was when the problem started occurring.

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There is one other failure that cause kickback and that is an ACR failure on the camshaft; although, washing the outside of engine can't cause its failure. They however do fail at any time.

In Reference to post #3.

To check for an ACR you remove the valve cover. You then rotate the engine normally though while watching the valve rocker arms. As you approach TDC compression stroke both valves will be closed but one will open slightly for a split second to release some of the compression. On the P61, P65, and P70 engine it would the lower rocker arm that does this which appears to be the exhaust valve. If no movement is observed and the valves are adjusted to spec then the ACR on the camshaft has failed.

Valve specs are .003-.005 Intake and .005-.007 Exhaust.

StarTech said:

There is one other failure that cause kickback and that is an ACR failure on the camshaft; although, washing the outside of engine can't cause its failure. They however do fail at any time.

In Reference to post #3.

To check for an ACR you remove the valve cover. You then rotate the engine normally though while watching the valve rocker arms. As you approach TDC compression stroke both valves will be closed but one will open slightly for a split second to release some of the compression. On the P61, P65, and P70 engine it would the lower rocker arm that does this which appears to be the exhaust valve. If no movement is observed and the valves are adjusted to spec then the ACR on the camshaft has failed.

Valve specs are .003-.005 Intake and .005-.007 Exhaust.

Click to expand...

didn't know the powersource 173cc motors had an ACR (compression release?). I just replaced a cam on a briggs 21 hp rider.

Yes according to service manual Powermore engines do as do most engines. Even very old engine had bump or ramp decompression grinds on the camshafts. The only engine without them is usually the ones with hydraulic lifters.

Have replace quite a few 793880 camshafts on Briggs engines due to ACR failures. But I just replace one that the exhaust lobe was nearly completely worn round, a first for me to in 10 yrs and it didn't have a broken ACR. Saving that ACR for later use. I actually keep or two 793880 in stock all the time now just because of the ACR failures.