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Motor starts and runs, but keeps speeding up and slowing down. Governor is fluctuating, but it also backfires. I cleaned the carburetor and it was full of gunk, but no help. So I replaced the carb, still no help. This is a 31C7071346B1 engine. Hooked up a timing light and it would strobe, but about the time the engine would misfire, the strobe would be off. I'm thinking I was losing spark. I pulled the flywheel to check the key, it was slightly cut, so I replaced and torqued to 100 ft-lbs. Still fails. Checked the plug, gapped at .030. Cranked engine with plug removed and plugged up. Seems to be firing fine. Anybody have any other suggestions would be greatly appreciated.

It seems to me you have the infamous Nikki carb on that engine ?? Am I right ???

Those carbs are known to hammer the gov......... You may have to take it back apart and do a complete clean out including the welch plug...... A good soaking in a carb dip or a ultra sonic cleaner then you have to press it in back in with a punch....

Or the gov it out of adjustment..... I have worked on 2 different mowers this past month that other people have worked on before I did and both govs were out of adjustment....... On their part of their repair....

Sometimes over the years govs need to be set again.........

Let us know Mon Ami ~!~!

Boo has a great link for these Nikki carbs... He will Chime in later ~!~!~!

Boudreaux In Eunice La. said:

Boo has a great link for these Nikki carbs... He will Chime in later ~!~!~!

Click to expand...

BO, ..IF this pictorial on the Nikki carb is what you think I should post.. so be it !!

http://outdoorpowerinfo.com/repairs/briggs_intek_single_ohv_nikki_carb.asp

I also have personal pics of the springs and linkages if needed ..........

Boudreaux In Eunice La. said:

It seems to me you have the infamous Nikki carb on that engine ?? Am I right ???

Those carbs are known to hammer the gov......... You may have to take it back apart and do a complete clean out including the welch plug...... A good soaking in a carb dip or a ultra sonic cleaner then you have to press it in back in with a punch....

Or the gov it out of adjustment..... I have worked on 2 different mowers this past month that other people have worked on before I did and both govs were out of adjustment....... On their part of their repair....

Sometimes over the years govs need to be set again.........

Let us know Mon Ami ~!~!

Click to expand...

It is the Nikki carb. My daughter has the same engine with the same carb, so I swapped it and got the same results. Gov. adj. might be something to check into. A little background on mower. It was given to me just to haul it off. It had been worked on by someone previously. They had but the wrong shroud on( one for a 17.5 instead of the 20.0) The numbers on the valve cover are for the 20.0 hp. They also hung a huge spring on the choke to keep it pulled back, so know telling what else they did. Can you tellme how to adjust the Gov?
Thanks,
Ricky

Here's the Shop Manual, ....... for governor adjustments, (external) see ..SECTION..1 - Page 18
BE SURE you are reading the procedure for YOUR MODEL of engine !!!!

Further Governor adjustments (internal) may be found in SECTION..5

https://docs.google.com/file/d/0B6NaqjIxWV1ybEN0LWo3azl6OUU/edit