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ORIGINAL: supertib

I have both motors.... I have had multiple Jammin and Picco 28's and just one OS 28..........As said before both motors have killer bottom end but the OS seems to have better top end run out.... Both motor idle extremely well, the Jammin is less prone to loading up tho, not that its an issue with either motor...but the Jammin always maintains crisp trigger no matter how long it idles...... Neither motor is perfect, my OS 28 had its front bearing start leaking very badly by tank 10, the carb boot leaks and the carb base leaks.... All easily fixxed, but still not perfect......... the Jammin carbs can be leaky so sealing is IMHO mandatory....... The Jammin uses a harder piston and definitely holds its pinch much longer, the OS 28 lost its pinch somewhere around tank 10 which worries me the piston is of a softer metal.... The jammins on the other hand will carry pinch for many gallons, at gallon 6 many still will stick at TDC..... But even tho my OS 28 has no pinch it still has great compression, but for how long I am unsure, but judging by how fat it lost its pinch I suspect the engine will wear fairly quickly..Both motors use good quality steel on the cranks, OS V-Specs are known to wear crank pins but I am unsure of the OS 28...I do know the Jammin have a oversized crankpin that I have never seen wear out of round...... The Jammin will wear it connecting rod if anything, so I recomend monitoring rod slop, usually the only failure point in a Jammin is the connecting rod........

The OS has the better powerband, the Jammin is more durable, the OS is a little easier to tune, the Jammin idles better..the OS is better on fuel...... both hit very hard in the low end and too much power for 90% of users... I do not think a person could go wrong with either engine....