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12,259 Posts
Discussion Starter #1
How about we post up pics of various carburetor setups on Roadsters, places to buy manifolds or complete kits, and other valuable technical information like the 5kΩ TPS mod by Maui Miata.

I'll get this started by posting up a pic of the Keihin FCR flat-slide carbs. These can be purchased used (came on some high-performance Japanese motorcycles in the 1990s) or new from places like Jupiter Net Car Garage among others.

 

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Discussion Starter #2
Better TPS by Maui Miata

I've built a better Throttle Position Sensor. It's a 5K Ohm pot attatched to the throttle shaft. See attatched pics and schematic.

I fabricated an M5x.75 screw to duplicate the shaft that was in the pot, complete with flat spots to locate it in the pot. After drilling and tapping the throttle shaft I screwed in this new shaft with a little thread lock applied. I used the nut on the pot to secure it to the bracket which also serves to make it adjustable.

I have it adjusted so that starts out at 4.4 volts at idle droping to 1.2 volts at WOT. It's entire sweep is 1/4 turn of the throttle and that's why I used a 5K pot. Works out about right.

Ignition timing at idle is 10 degrees BTDC and at WOT it goes to about 35 degrees BTDC. I've changed the timing both ways and 10 degrees seems to be the sweet spot, even with carbs.

I've got the bottom end and the midrange tuned pretty well, I just need to get the top end a little stronger 5K and up. A change in mainjet size perhaps.




 
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