Topic: CB500 advance mechanism differences.

[Scott S]

 I thought I had my '71 CB500 sold and noticed something odd today.

 The buyer asked me to install the Tytronics ignition. I got it installed and can't get the timing right. It doesn't seem to advance and runs rough in the upper RPM range. I had it running pretty good on points.
 The points plate is a TEC unit.

 To install the Tytronics, you remove the cam on the advance mechanism. I went to install it today and double checked where the "dot" is supposed to go. It should be about 4 o'clock, pointing to TEC on the advance.
 Here's where it gets weird. I cannot install the cam where it is in the correct position. Installed, it's pointing at about 7 o'clock. Turning it 180 degrees, it points at 1 o'clock. This is the advance mechanism that was on the bike when I bought it.

 The advancer has 323 stamped onit, as well as AD125-02, and a stamped emblem of some sort.

 See pics.


 

[Scott S]

 I dug around in my stash and found a TEC mechanism. The dot is at 4 o'clock, as it should be.

 I thought the bike ran OK with points, but the cam position is completely different on the TEC plate. Maybe that's why the electronic ignition couldn't be timed properly? Maybe I left something on the table by using  that mechanism, even with a good TEC points plate?

 What am I looking at here? I'll use the TEC advancer, and now I'm wondering if I should start it on points again or try it with the Tytronics?

 Here are some pics of the TEC unit.

[CycleRanger]

The second advancer is a Hitachi part.

I wonder if the Tytronic package has the wrong rotor.

[Scott S]

 I had this Tytronics on a different bike without any problems.

 Was Hitachi OEM? Or an aftermarket part?

 The cam lobe on the Hitachi unit looks to be shaped differently, by eyeballing it.

[CycleRanger]

I had this Tytronics on a different bike without any problems.    -Ah, ok.

 Was Hitachi OEM? Or an aftermarket part?

 The cam lobe on the Hitachi unit looks to be shaped differently, by eyeballing it.

Honda used both Hitachi and TEC advancers.

[Scott S]

 The cams sure look way different on them.

[HondaMan]

Don't overlook the possibility that someone in the past swapped the cam on the advancer? This happened to me, and more than once (but on different bikes).

The AD125-00 and AD125-01/02 units have similar stamped numbers, but apply to different bikes. The "323" is for the 500/550 engines, the "300" for the 750 (although I've found them on CB400F from time to time, too).

[Scott S]

 I just wanted to follow up:

 I put the points back on with the same Hitachi advancer. Bike runs great now!

 I have used Tytronics before with great results. That exact unit was on a different bike, but with a TEC advancer. I couldn't get it to advance with the Hitachi unit. I'm wondering if the Tytronics rotor was rubbing or binding somehow?

[scottly]

The Hitachi advancer on my 750 had a pin sticking out on the side that fit into a groove on the inside of the cam. It was necessary to remove the pin to fit the Gerex rotor, and the same for a Dyna rotor. The TEC advancers didn't have the pin.

[Deltarider]

The Hitachi advancer on my 750 had a pin sticking out on the side that fit into a groove on the inside of the cam. It was necessary to remove the pin to fit the Gerex rotor, and the same for a Dyna rotor. The TEC advancers didn't have the pin.

This ^ and what Hondaman mentioned: make sure either you or the PO didn't reassemble the cam 180^o degrees out.

[HondaMan]

...make sure either you or the PO didn't reassemble the cam 180^o degrees out.

I wish I could say I've never done that...

[bryanj]

There were two different advancers on the 500, one of which is quite rare but either work fine

[jonda500]

...make sure either you or the PO didn't reassemble the cam 180^o degrees out.

I wish I could say I've never done that...

`I don't wanna say how long it took me to realise that this was the reason I had to switch the yellow and blue wires to get my 400-4 to start after overhauling it back in the late eighties, John

[HondaMan]

...make sure either you or the PO didn't reassemble the cam 180^o degrees out.

I wish I could say I've never done that...

`I don't wanna say how long it took me to realise that this was the reason I had to switch the yellow and blue wires to get my 400-4 to start after overhauling it back in the late eighties, John

Yeah...that was how I "troubleshot" what I did to the advancer...