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Hi Jon

I have been wondering, Is it possible to give a bike more low end torque by reducing or removing the reed valve spacer?


In theory it would reduce low speed torque by shortening the standing wave in the intake tract. This would be slightly offset by an increase in the "Primary Compression Ratio" which is the ratio of the trapped volume in the crankcase with the piston at TDC and BDC. A higher PCR ups the low and mid range but if taken too far, results in a flat top end because of what is called "pumping loss"- the energy absorbed by the piston having to compress the mixture on the downstroke. Then you get into turbulence, reflected wave in the exhaust tract and a bunch of other factors to consider when building a racing engine. It's a matter of balancing the known variables to provide the type of power you want the engine to put out.

The reed valve spacer serves several purposes as far as I can see on a Trials bike: 1) making the intake tract longer 2) better shaping the intake charge 3) lifting the carb off the cases to prevent heat/vibration transfer and thereby reducing fuel frothing and keeping it more dense by keeping it cooler and 4) unblocking the transfer/boost ports for better flow. I have a 96' 370 and added a spacer when I went to a 28mm Keihin carb, which works great. The 97' and up Gas-Gas's came with the carb spacer stock.


Professional tuner and 'Trials Competition' writer Jon Stoodley has very kindly stepped up to the plate to answer your questions. If you're having problems, or need some advice just send an email to Jon. If it's something that could be useful to others, we'll post it on the site.
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