Topic: Ignition A/R unit

[mad mike]

Advice please,  .... Ref CB750 race bike build,  Is there any advantage in using a specific model of advance / retard unit when using a Boyer electronic ignition and coil setup,  ...... The bob weights and springs have to be removed from the a/r unit as the advance is built into the electronics, I seem to recall reading on this site that some A/R units have the fully advanced mark in different places varying the firing position ?  .... thanks in advance .

[HondaMan]

There is a slight amount of difference between the 3 types of spark advancers found in the 750 engines. The earliest ones are often marked "AD125" and have the shorter idle advance (by about 2 degrees) and advance the fastest (softest springs). The later ones are marked with the tiny Hitachi stamp or the TEC stamp: they have 2 degrees more idle advance, but the same full advance. The ones for the 750F2/3 engines have the same advance rate (in the springs) as the Hitachi version, and they are often stamped with "410" on them somewhere.

But, any one of those, or any one from a CB500/550, would work fine if you just need the cam to be locked in place and let the electronics do the advancing. You can also buy a brand new one, albeit with bizarre springs, from 4into1.com.

[mad mike]

Thank you "honda man" you are a veritible "goldmine " of information, ..... I have several A/R units to choose from in my collection of bits, so it appears it doesn't matter which i use as all the "gubbins" of the A/R are dispensed with [including the cam]  when using a Boyer ignition. .... Many thanks for the advice from "sunny" england.