We struggled a bit with the first 12.90 engine we bought, but got back on track with a stroke of luck when we discovered that a long forgotten 5HP Briggs engine stashed in the basement was a perfect fit. We now run right where we want, 12.90's to 13.10's depending on the weather.
So, we decided to tear down the first engine since its best run was in the high 15's, and no matter what we did it only ran slower - eventually running in the 19's & low 20's, (this is in the 1/8th!!)
This is what we found, [img]<<GRAEMLIN_URL>>/mad.gif[/img]
Lifters:
Bummer, looks like it held water for awhile and made the cam wear away.
To make matters worse, the rod bolts rounded off when we tried to remove them. So, we took the bolt heads off with a Dremel tool. The rod looks pretty good, especially for not having a rod bearing - it rides directly on the crank. The crank is done though, the rod surface is quite pitted.
We'll rebuild it over the winter so we have a backup engine!