Lesson Learned - Be careful with Slant Heads
Was working on a friend's motor & saw that his slanthead was all cracked up around the sparkplug hole. Since we were trying to diagnose the location of an air leak, figured that would be a good place to start so I threw my straight head on there. Motor seemed real hard to turn at first but then it finally started turning but wouldn't start. Pulled the head back off & the piston had actually snapped the electrode off the sparkplug. Luckily, the piston doesn't seem to have a mark on it, but I can't find the electrode anywhere.
Upon further inspection, I realized the slanthead had a piston with a round top, and the straight head was flat on top. Meaning the round spot on the top of the piston was probably coming up higher. Replaced the spark plug with a shorter one and it runs fine (but the airleak is still there unfortunately).
Just thought I'd save some of you a headache...