The truth about big bore kits for 139qmb

Big bore kits are mislabeled folks

Here's a list of the most common big bore kits for the 139qmb and the actual sizes.

120cc bbk = 88cc aka 52mm bbk

105cc bbk = 88cc aka 52mm bbk

100cc bbk = 81cc aka 50mm bbk

80cc bbk = 72cc aka 47mm bbk

70cc bbk = 63cc aka 44mm bbk

If you have questions contact me anytime!

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[bryanharrison]

I think the reason they market a 50mm piston as 100cc is in the instance that you stroke it. If you stroke it it gets closer to 100cc but I don't know the exact number

[theilluminatimember]

Do you need to modify the case to fit any big bore kit or will it always be a straight swap?

[seanmayo]

Ah I say look at the crank case inlet an I want say no company name or whatever I was told the 1p39qmb was built to be a 72cc which I seen an heard an it just as well been a 50cc so . Im confused. The 51mm piston an the 47mm is night an day .

[MusaToci-mi]

so true bro i see guys using bigg bore kit still 45kmph they got 😂😂