Hi Gurus The ZXR250C that I’m working on only has one throttle cable. Does it really need the closing throttle cable? I’m assuming it should but before I track one down I thought I’d ask. I know it’s a ‘mod’ on motocrossers to remove it… Thanks for advice
Technically it is a safety item in case of throttlebodies getting stuck wide open. Not really a problem on small bore carbs, there is almost no chance of the throttlebodies getting stuck open due to engine vacuum. I have had several bikes with worn out cables or a broken closing cable, and removing it did nothing bad, in fact it was an improvement.
Closing throttle cables are important when running flat slide cards (as opposed to ones with a butterfly valve). The vacuum applied to the slides on closing causes them to bind up. You can really strong return springs (as I do on my race car, as its a bit hard to hook up a return cable to a pedal). But strong springs are a pain on the wrist.
The wiring loom main section runs above the throttle mechanism on the carbs (RHS looking forward). There's a clip on the frame (and one on the carbs I think) to hold/stop the loom from falling down into the mechanism and potentially causing the throttle mechanism to remain open. Other than that possibility, there's no reason other than roadworthiness (it would fail a roadworthy in Australia) to have a return cable.
