Topic: Limited Advance

[DV Red Herring]

Today's question... Why would my ignition advance not reach the two hash marks? Dwell is set at 25*. Dynamic timing is a few degrees advanced. The advancer springs are in good condition, and the advancer is clean and lubed and in working order. The bike runs really well. Is there even any need for more advance?

Edit: Dwell was set at 26° not 25°

[DV Red Herring]

Oh yeah. CB750 K4. 300 advancer.

[Don R]

 Have you taken the advancer off and cleaned it or checked movement?  You can mark the points plate and the engine case with a sharpie so it's easier to return to correct timing.

[DV Red Herring]

Yessir. Been there, done that. I can't find anything wrong with it. It just doesn't advance far enough.

[Paintedseat]

Is your battery charged?

[Deltarider]

Dwell is set at 25*.

Please specify on what scale. Try a dwell of 23^o (8 cyl. scale) and I bet you'll reach full advance.
If not:
a) Does your timing light happen to be the type that you can dial the desired degree of full advance so it flashes at the 0^o mark? If so 'zero' that dial.
b) Did you possibly lube the dissassembled advancer with some sort of grease that has gone hard and so possibly hinders the advance?

[Bodi]

Set the timing at full advance to be on the advance marks. Idle advance will not be "exact" but it just doesn't much matter. You will be doing 99.999% of your riding at full advance. Performance is very much affected by advance and you want it to be at least at the factory marks. The factory full advance is a safe setting that avoids detonation using 1970s regular fuel.
Dwell meter readings are funky with these bikes, the meter's scale settings are for distributor systems on multicylinder car engines. I don't know what scale settings and readings are appropriate, I adjust dwell via the gap measurement.

[Yamahawk]

Today's question... Why would my ignition advance not reach the two hash marks? Dwell is set at 25*. Dynamic timing is a few degrees advanced. The advancer springs are in good condition, and the advancer is clean and lubed and in working order. The bike runs really well. Is there even any need for more advance?

I am not sure that you have to lube the advance mechanisms like the old Brit bikes had to, but clean is important. Lube will attract crap, so you may want to get some brake cleaner and clean the advance mechanism. Do you think perhaps a PO has squeezed the advance mechanism 'ears' a little too much? That was part of the Hondaman recommendations for fixing a mechanism that had too much advance. Just something to check, as if you set up the timing statically, and point gap is good, perhaps it may be what is happening, and it isn't hitting full advance with a timing light set to 0deg. advance.
Charlie

[PeWe]

Dwell meter is good tool to get SAME point gap on 1-4 as 2-3 and the engine will run better.  I use V8 setting, 23-24.5 degrees is the range I have read on this forum. My engine is very happy with 23-23.5 degrees. Same on both points. (or as close as possible @ high idle 1200-1500 rpm.  23.2 vs 23.3 is OK, you will hear when it runs best.

Set ignition (after correct point gap) to reach factory full advance around 2500-2700 rpm. The condition of the springs will  affect this. My engine had too sloppy adv springs wich caused way too early full advance.
Both springs cut 1/2 wound and reshaped. Full advance after that will happen at around 2600-2700 rpm, idle@1200 rpm 'F' lines up with case mark.

I have an alternative case mark (~2mm to the right)  since advance plate has a play when nut is not tightened. I have measured (before timing the cam) with piston stop to find correct TDC.
If moving the adv at max counterclockwise, the real TDC is correct  T lign up with case mark. (F will then be correct too relative the case mark)

If the advancer is at its clockwise position I have to let 'T' and 'F' on advancer plate align with case mark about 2mm later.

[DV Red Herring]

Okay. I reset dwell to 23.5 degrees on the 8 cylinder scale. With no other changes this allows my timing to be just slightly advanced at 1200 rpm and it reaches full advance around 2800 rpm and holds steady from there. I took her for a ride and she runs strong throughout the rpm range and idles steady at traffic lights. Although I haven't tested the factory redline, it pulls strong to my self imposed line of 8000 rpm. This forum and these tools are the best resources for tuning these bikes. Thanks gents.

[Yamahawk]

Cool! Glad you got it sorted!!
Charlie

[DV Red Herring]

Yeah. The difference in timing was killing my ocd. The actual difference? I don't know. It ran like a raped ape before, and runs just like a raped ape now. But I'm not a fan of the silent killers in engines, so better safe than sorry. The old school tools and info here made a night and day difference from feeler gauges and test lights to now. It went from a decently running machine to a properly running one. Appreciate the comments and suggestions.

[Yamahawk]

Man, I just missed out on a nice timing light with compression gauge and fuel pressure gauge set on eBay, I was ready to accept the $30 counter-offer when someone bought the set...
Charlie

[DV Red Herring]

Yeah. You gotta be quick. It's survival of the fittest on there sometimes. I can't count how many deals I've pooched on there.