Engine Stumble?

Yesterday while doing pattern work (full stop and taxi back) I had what I think was an engine stumble on the fifth pattern abeam the numbers and on base at about 1200 rpm's. I had been out about 1.3 hours with the landings and taxi backs at the end of the flight. I also had to hold on the ground some for traffic. The temp was in the lower 80's. This is the first time I have noticed this and also the first time I had worked in the pattern (and ground) this long. I had the electric fuel pump on in the pattern but not on the ground. Any idea if this could have been vapor lock or other problems? RV-7, IO-360-M1B.

Thanks for any insights.

I had a similar experience yesterday. DanH's reply...https://vansairforce.net/community/showpost.php?p=1531093&postcount=2 . It confirms something I thought I'd read about engine fuel pressures on hot days. Might be applicable in your scenario.

...Or it could have been an errant piece of carbon fouling one + of the plugs.

Did it clear up?

Thanks for the input.

That was my last landing and pulled back to the hanger. I will remove the cowling before next flight to look around for sure. It seemed fine back on the ground. I was ready to call it a day. I am at 31 hours on phase 1.