Topic: Early cb750 F spark advancer and interchangeability

[macvit7906]

I did a lot of searching on the forum and found many good posts about different model spark advancers and what their differences where.

However, I did not find any answers specific to my situation.

I'm currently rebuilding two F0/F1 engines and i'm looking at two different advancers. The parts Fiche tells me I need part# 30220-300-154 which is the advancer stamped "300"

But out of one engine came the advancer on the right in the below picture stamped AD125-01.

Question - Can I use this AD125-01 advancer in a stock F0 engine? Will I have to make any modifications?

If I can't use it, anyone out there have a "300" advancer they would like to trade?

Thanks!

[robvangulik]

With a strobe light it is easy to check if they behave different, at what revs does it start to advance and when is the advance complete, what revs and how many degrees.

[PeWe]

I think the AD125-01 advancer sat in the 1975 F.
I have one advancer I think I bought with other F0 parts.
 
I'm sure you can use both in any CB750. It's still same engine.

This has been discussed before in a thread somewhere.

[scottly]

The one on the left is made by TEC, and the one on the right is Hitachi. Also, on your TEC unit, the points cam is turned 180*. Notice the dimple on the edge of the cam at about 10 o'clock; it should line up with the hole in the base next to the TEC logo.

[macvit7906]

The one on the left is made by TEC, and the one on the right is Hitachi. Also, on your TEC unit, the points cam is turned 180*. Notice the dimple on the edge of the cam at about 10 o'clock; it should line up with the hole in the base next to the TEC logo.

Ah I see. So both will work?

Thanks for pointing that out, I would have never have known that - took it apart for cleaning.

[scottly]

Better you fix the rotor now than trying to figure out why your bike backfires and farts but won't run.

[macvit7906]

Thanks all

What do you recommend for lubing toe advancer? I've ready that oil is a bad idea ad I should use a light coating of grease on the cam and weight pivots?

[pjlogue]

The advancer on the right has slightly greater advance  at both idle and full advance than the TEK 300 and the advance comes on sooner as the springs are smaller diameter (weaker)  Both will work in your bike.

-P.

[macvit7906]

The advancer on the right has slightly greater advance  at both idle and full advance than the TEK 300 and the advance comes on sooner as the springs are smaller diameter (weaker)  Both will work in your bike.

-P.

Thanks P. I have a stock engine and an 836 bore (ported head the whole 9, dyna S electric ignition). Would using one or the other make a difference?

Recommended lube for the advancer?

[pjlogue]

The AD125-01 (earlier version of the 300) will be faster on throttle. (faster to rev up)  I don't see why you can't use it on your engine if you set everything up properly.  The 1969-76 had 3 versions of the spark advance.  Spring tension on the weights was increased and the advance (both idle and full advance) were reduced in each version.   Swapping your for a 300 isn't an even swap.  The AD125-01 is harder to find. 

-P. 

[HondaMan]

For lube: while you have the cam off the advancer, dab some grease on the shims (both) and the shaft under the cam.
The Hitachi AD125 advancer was found on the Old Factory K1 and early K2 engines (and occasional late K0), while the engines made in the New Factory came with the TEC advancers. They corresponded (in their original engines) with the AD units being found when cams opened at 3-4 degrees BTC intake, and on the F0 with the Stellite valve guides and the original F0 cam. They are quicker to advance, IMHO a little too quick. My K2 has one, and both springs were cut off 1 full turn to make the low-end torque stronger for touring and to reduce plug fouling when riding in city traffic for hours on end.

They are also the advancer shown in the original Honda (green paperback) manuals, and their mention in there of aligning the cam's mark with the "logo" (Hitachi's double circle) often causes the later ones to get assembled backward during rebuilds, as those align like Scottly said above, instead.

[PeWe]

I checked my AD125-01 advancer a few days ago. Its springs are really good, not as soft as my 300 advancers were as I had to cut.
I have Yamiya racing springs, they are a just little bit softer than the old stock "low mile" AD125-01 springs. Spring force equal, intial play of the rotor a little bit more. Maybe spring lenght that differ just very little.

I'll might test this advancer and see how it will act. Set F at idle (1200 rpms) and see when full advance occur, hopefully after 2500.  The advancer has its stock springs.
Then a road test.... maybe with my old Dyna-S just for fun on my blue K6 that has really good torque. Improvement or opposite will be revealed easier on this bike.
EDIT:
AD125-01 advancer came in with cut springs, Dyna-S.
Ignition set at 1100-1200rpm, full advance at around 2600-2700rpm. Engine runs smooth from idle to top (max 9500rpm on dyno) Megacycle 125-75 cam.