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Hi all,

Back with a new question to the group...

Just trouble shooting some small problems with the px... nothing serious but waiting for a few parts to update the engine, before carrying out with jetting the pwk airstriker...

But I found that as I'm testing the vespa, I'm actually getting quite a bit of blowback through the carb, I didn't think about it too much before, but isn't the Reed valve suppose to get rid of the blowback?

Wonder if anyone has any insights on potential reasons? I checked the Reed petals... no gap, chips or broken parts

Just for FYI, It's happening at 1/4-1/2 throttle
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Lucky
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Lucky
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I've always had some blowback with reeds. Seems inevitable that a pressure-operated device would have a little.

Do you see it consistently holding 1/4 throttle, or is it a blip as you pass 1/4 throttle and the motor just hasn't caught up to draw the increased flow as it revs up?
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chandlerman wrote:
I've always had some blowback with reeds. Seems inevitable that a pressure-operated device would have a little.

Do you see it consistently holding 1/4 throttle, or is it a blip as you pass 1/4 throttle and the motor just hasn't caught up to draw the increased flow as it revs up?
It's if you blip past 1/4 throttle... but that's a good point... I haven't noticed what happens after 1/2 throttle as I haven't done that stationary... if I remember correctly... it has blowback at higher revs too...

It's interesting, the blowback was less with the rotary crank installed... just looking back at old videos... maybe it has to do with the pressure being able to go past the crank now?
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Jet Eye Master
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Jet Eye Master
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Most of the blowback will be because the jetting is no good. 2 strokes will always have blowback from the carb and spooge from the exhaust but how much of each is acceptable? This is the big question. Conversely, if your 2 stroke doesn't have any of either.....panic!
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Jack221 wrote:
Most of the blowback will be because the jetting is no good. 2 strokes will always have blowback from the carb and spooge from the exhaust but how much of each is acceptable? This is the big question. Conversely, if your 2 stroke doesn't have any of either.....panic!
Jetting makes sense... but makes me wonder which way makes it have blowback...? Too rich or too lean... and which sections of the throttle?

Conventional wisdom would point towards over rich causing lots of blowback, but I feel it's not and is caused by pressures in and around the jets...
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