what is a boost bottle?

[kwellsqpr1]

my m8s just asked me what a bost bottle is
https://cgi.ebay.co.uk/Boost-Bottle-Stage6-Yamaha-Aerox-Peugeot-Speedfight_W0QQitemZ300128060716QQihZ020QQcategoryZ25640QQrdZ1QQcmdZViewItem

hes thinking about buying it. is it worth it. what will it do?
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keeping it rubber side down

[stinkwheel]

It's just an empty bottle. Sure, it is made of tarty anodised stuff but in essence a rigid plastic bottle of the same volume would have the same effect. There is fuck-all in it. It is an empty bottle with a hose-tail on it.

They fitted "boost bottles" to small 2-strokes as standard in the mid 1980's. If the fuel blowback from the engine was too much for the reed valves to cope with, the pressure wave diverted some of the unburned fuel mix into the boost bottle instead of dumping it back into the airbox. If the engine then tries to run lean, it'll pull the fuel back into itself.

It is a strategy for coping with poorly setup carburettion, usually due to fitting an unecessarily large carburettor. If your carb is setup badly and running rich on full chat, a boost bottle will give a slight increase in BHP. Otherwise it is a waste of time.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.