Topic: the impossible "F" mark

[knobbs]

Hello 1974 cb750. stock motor with 4?2 pipes and pods.
I have carbs right where I want them so I checked the timing with a timing light and there is no way I can get the timing mark to line up with the "F" mark. The beat I can do is the 1 on the 1.4.
Any Ideas
Oh Idle is at 900 RPM

[lucky]

Any carb tuning comes last.

Just get the static timing correct. Forget about the timing light.
The timing light is to check to see if the advance timing is right,and it has to be 2500 rpm or more.


Just set the static timing and forget the rest.
The only reason to check with a timing light on these old bike is to see if the advance unit is working.

[chickenman_26]

Hello 1974 cb750. stock motor with 4?2 pipes and pods.
I have carbs right where I want them so I checked the timing with a timing light and there is no way I can get the timing mark to line up with the "F" mark. The beat I can do is the 1 on the 1.4.
Any Ideas
Oh Idle is at 900 RPM

Lucky apparently didn't understand you. Just to be sure that I do - You're observing the timing at 900 rpm and can't get it to retard past the 1 on the 1-4. Correct? Okay, it's too advanced. But just to be sure the advancer isn't hanging up, check at 2500 rpm. If the timing advances beyond the full advance marks, that confirms the advancer is working. If so, your issue is caused by either too great a point gap or the main point plate being rotated too far counter clockwise - maybe both conditions together. The points must be filed flat to get an accurate setting with a feeler gauge. .012" to .016" is acceptable. Shoot for .014". Then either set the timing statically or with the timing light - timing light for best accuracy - by rotating the main point plate as necessary. Then check that the timing mark falls between the 2 full advance marks at 2500 rpm or above. Now do the same on the 2-3 points, but adjust the timing by sliding the sub-plate under the points either clockwise or CCW. Don't move the main point plate when adjusting 2-3 timing.

Stu

[bryanj]

Sorry but in 30+ years the ONLY thing to use a timing light on is to check the advancer is working, Honda in the manuals tell you to do it static, do yourself a favour and give your timing light away!!

[Jasondo]

I agree with chicken man. Listen you dont need to set it to the f mark. Just crack the throttle to about 2500rpm and set the timing with a strobe light to be inbetween the advancer marks. and always use a strobe light to set timing. It's the fastest most accurate way.

[Bodi]

timing light 100%.
static is just to get it close enough to run, so you can use the timing light.
knobbs is right, set them at full advance (2000+rpm) and don't worry about the F marks at low rpm - if the advancer isn't stuck of course.
set gaps first.
set 1-3 timing.
use the daughter plate adjustment to set 2-3.
the main plate may be a loose fit, that makes timing a bugger to set because you mess up the gaps when you move the plate. shim it to a snug fit if thats a problem.

[HondaMan]

Timing light is a must on these bikes, today. The main reason: our parts supplies are not often Honda OEM. In particular, the problem you're describing comes from Daiichi points, made in China, that are geometrically incorrect. Look closely at yours, see if they have tiny tiny imprint that resembles a pointy 3-leaf clover: those are the offenders. There are also some out there from FEW that do this same thing.

The situation is this: the points pivot is off-position by 1.5mm and the foot of the rubbing block is too long. This combination makes it impossible to set the timing back far enough to reach the "F" marks (both 1-4 and 2-3, if both are Daiichi parts) even with the points gaps set WELL outside the spec of .012"-.016". The points cam only lifts about .024" total, and the adjustment slots only reach .020" anyway, so it is simply not possible to make them work directly.

If you can't buy some new Honda points (the whole plate assembly is the very best, made by TEC today), it may be possible to bend the grounding arm and the rocker carriage a little and get the marks closer, but the points will then wear out very quickly from the twisted forces that will occur. It might get you home one night, though?

[Bootlegger56]

I think Western Hills still has TEC points and they are pricey but then if you install the HondaMan ignition you don't ever need worry about replacing them again.

[jamesbekman]

If your cant get it adjusted to the F mark you need to widen the points gap first.  Its super easy once you realize that its a factor in the matter.

[74750k4]

Ultimately you need to know/set total advance. That is where your power is being made while riding. That is really the un-retarded position of the advance mechanism. Static, retarded, initial timing is very secondary to this, although you could get it idling, and running that way.  Above 2500 RPM you need to be (un-retarded) fully advanced at least as far as the double slash marks, unless you are pinging under load, then you should use higher Octane fuel, or retard, til' that stops, or possibly try advancing some more if no pinging. So, you could get away with setting your timing by the ping method in a pinch, but a timing light helps, especially to get your balance of 1-2, and 3-4 at full advance. I would not assume that if I set my initial timing, that my full advance was going to be correct. Too much advance at initial will cause hard starting, or overheating. Setting initial is great for an idling bike. Setting the fully advanced (un-retarded) timing is going to set the power capability for the fuel you are running. Low grade fuel... lower settings of advance. 100+ octane...  higher advance is possible.