No it doesn't matter where the poppet value is positioned just as long as it seals properly.No you don't need to prime it twice as much.They don't use much fuel.In fact they use less than a 160cc.
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I am looking for a workshop manual for my 170cc twin
These manuals are hard to find they do come up on eBay from time to time.
This is what the cover looks like.
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...and before you ask yes I do have a copy that front cover is of my copy.

Here for a good time,not a long time.