Uploaded July 2019 | Updated September 2026, 2 hours ago
Mobylette AV7 leak down test (bad crank / SPI seals)
This is a 50cc setup that I have a hundreds of miles on. Noticed of late it started having a slightly higher idle than normal, and wasn't running as it should. Some days it would run just fine, but after about 15 minutes, it developed an odd 'stalling out' at speed. Once slowed down/cooled down it would run fine again, but eventually would have the stalling again.
Plug looked good, cylinder piston looked good via inspection camera, and COMPRESSION was good as well. However with these AV7 engines, their crank seals are known to get weak and suck air in (while holding pressure from the inside).
I found an old party straw, and taped it to the intake to make a good seal, rotated engine around to block off the exhaust and instantly found my issue.
Mobylette AV7 leak down test (bad crank / SPI seals)
This is a 50cc setup that I have a hundreds of miles on. Noticed of late it started having a slightly higher idle than normal, and wasn't running as it should. Some days it would run just fine, but after about 15 minutes, it developed an odd 'stalling out' at speed. Once slowed down/cooled down it would run fine again, but eventually would have the stalling again.
Plug looked good, cylinder piston looked good via inspection camera, and COMPRESSION was good as well. However with these AV7 engines, their crank seals are known to get weak and suck air in (while holding pressure from the inside).
I found an old party straw, and taped it to the intake to make a good seal, rotated engine around to block off the exhaust and instantly found my issue.
