Topic: Ignition timing question, 750

[dragracer]

Its time for me to begin looking at setting up my dual magnet rotor button so I can use either a Dyna 4000 or my first choice of a Schnitz Racing Pro Series 2 ignition controller. Using a spare advanced, I installed a GS dual magnet rotor button over the shaft and it fit perfectly. It locked into the advanced arms easily also. The plan is to weld the arms in the full advanced position and use this as my base timing. The question is, what number is full advance with the arms fully extended?? The book lists 24-26.5 degrees at the marks on the advanced at 2500rpm. I assume this means the springs have allowed the arms to locked out against the stops or am I incorrect.

Obviously I'll be using a degree wheel she setting my static timing with the pro series 2. I've got to be sure where I stand before I plan on using nitrous oxide with the need to retard timing approximately.

Thanks fellas.

[dragracer]

Forgot the pictures

[scottly]

The question is, what number is full advance with the arms fully extended?? The book lists 24-26.5 degrees at the marks on the advanced at 2500rpm. I assume this means the springs have allowed the arms to locked out against the stops or am I incorrect.

The 24-26.5 degrees is from the F mark, which is something like 10 degrees before the TDC mark; I've measured it before, but I don't recall the exact number. Yes, the max advance is with the arms against the stops.
Is the GS rotor compatible with the Dyna and Schnitz pick-ups? Magnet to trigger spacing may be different. Why not use the rotor designed for the ignition you want to use?? 

[dragracer]

The GS rotor is for a Dyna 4000 or Schnitz ignition. Unfortunately there is no dual magnet rotor button for an SOHC. Luckily this rotor fits the shaft perfectly although its a tad shorter than a Honda single magnet rotor. A thin washer worked just right to take away the clearance. I've got to locate my Dyna S plate to be certain of the alignment for the magnetic pickup with the button. I'll play with the degree wheel on this junk engine to check my numbers before I  move forward with finalizing my choice of ignition controller. The plan right now is to use the Pro series 2. Its basically an all in one box. I'll set it up to retard the timing on startup to help alleviate cranking compression to save the starter motor. The box can retard and advance timing. It has low and high side rev limiters. It has a progressive nitrous controller built in. Autoshift function, shift light output, and a ton of other functions. I have them on 3 other bikes and have install at least 4-5 more for other people. This will be the first installation on an Sohc for me. My only dilemma is making sure I have the button set up correctly and that my static timing is a known quantity.

[dragracer]

So are you telling me that the max timing with the arms fully extended is 10 degrees plus 26.5, or 36.5 degrees before TDC??

[kmb69]

So are you telling me that the max timing with the arms fully extended is 10 degrees plus 26.5, or 36.5 degrees before TDC??

Yep, the "F" mark is 10 + the advance. Nominal 35 degrees total.

[dragracer]

Thanks Keith and Scottly.

Reading is fundamental. I should have been more vigilant in my quest for an answer before posting. 😞

[cbr954]

There are differences through the years, different tension of advance springs, different advance weights.  Hondamans book has a write up on the differences of the advancers throughout the years of the 750.

[dragracer]

Thanks for that insight Dana. I won't be using the springs because I'm planning to lock the arms by welding them in the fully advanced position against the stops. Knowing the degrees of full advance is the main thing for me. I'll set up the degree wheel to verify where I am.

[Don R]

Could you use a dial back timing light to see the exact advance?

[dragracer]

Could you use a dial back timing light to see the exact advance?

Once the bike is complete with wiring and engine running, I'm sure that could be done. All written documentation says 35degrees full advance so I'll go with that and double check the marks on the timing advancer with a degree wheel.