larryhobman
Scoot Enthusiast
Posts: 117
Location: Delaware beaches
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Post by larryhobman on Apr 27, 2018 20:08:57 GMT -5
I have a 3 wire tach +/- and trigger wire. I hooked it up to the coil and it is going crazy. Did I hook it up right or does it go to the trigger wire off of the flywheel. I hooked up the pos and neg direct to the battery for now. I may just have a cheap broken tach. Let me know please.
Going on a qmb139 so I can tune a 47mm kit
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Post by pinkscoot on Apr 27, 2018 22:45:30 GMT -5
Do you have a picture of the tach and where you got it?
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Post by cagiva4ever on Apr 28, 2018 3:33:38 GMT -5
1st determine if its made for 2T or 4T. or if it has wrong "stroke setting" in it.
also ,most 2T's have so called "waist sparg" at BDC, Hence tacho model and setting has to be right for 4T.
cheap, round in metal casing, eBay "Kege" tachos, have digital internals but with "analogue" needle, are same as 4T 139qmb tacho's on some scooters like XTR50.
i have 1 of them, and Kege pcb etc photos details++
Kege's take rpm/ign signal from 139qmb wiringloom, hence no "wrapping around HT-lead Conduction detection" like in most universal rpm tachos, that will easy False read rpm....
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Post by GrumpyUnk on Apr 28, 2018 10:16:37 GMT -5
I would have thought that 4T engines have a 'waste spark' as they fire on TDC, compression stroke and exhaust stroke. I thought 2T engines fired on each compression stroke, and it seems they would need another set of magnets/etc to have them fire at BDC. Why would they install a second set into the flywheel?
Regardless, I think some tachometers need to be connected to the wire attached to the ignition coil. The signal from the stator may be too 'rough', or you may have gotten the 'voltage source' from the stator that actually operates the AC CDI. The wire to the coil from the CDI is the one that will likely work, or, maybe the 'fire signal' from the stator, fed to the CDI. The source who sold the tachometer should have provided some indication of how it is to be connected. Some have multiple wires... two for lighting, two for power/ground and one for signal, the signal being used to operate the needle/display. tom
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