Topic: CB750 - Will not run without full advance - WHY?

[TheWiredNinja]

Just to preface, I have gotten great advice and help from a few of the guru's around here for my project which I certainly appreciate.  I have since narrowed down issue of problematic idling to what I believe is a timing/ignition problem - but I could be wrong in any case my specs are as follows:

1972 CB750
JE 836cc domed pistons 10.5 compression with modified cylinders (from CycleX)
Oversize intake valves with Mike Reick stage 3 porting and titanium retainers (new springs as well)
RC295 Cam
4 into 1 open exhaust
Dyna S with 5 ohm Magna coils

I initially had problems with idling with anything below 1800 RPM and it would otherwise rev and ride just fine (albeit, without proper tuning after the rebuild).  So I cut the advance springs by one ring given that I was getting full advance at around 1500-1600rpm.  Now the bike will not run as the advance kicks in later - I could barely get it started and when it did, it was completely bogged down and it would cut regardless of throttle input or choke position.

I initially thought it was a carb/tuning issue with my round-tops, so I gave in and purchased a Mikuni RS34 set from CycleX which was re-racked and richer needles were added by them (which I justified given the rest of my mods could be a nice improvement in power as well).  Initially I had problems starting the bike as before, so I removed one of the springs on the advancer to loosen the timing again, and it works while being free to rev (and better than before).  The problem is that timing is at full advance again (as expected) and it will not run otherwise.  It can idle at around 1500 RPM which isn't too bad and livable, but it's my understanding that in the long run, this will foul up the plugs easily.  If I lower the RPM to anything below 1500 RPM, while observing the timing, I see the mark starting to relax timing and that is precisely when the engine cuts out.

I'm still learning on using the new carbs and still have the old set but given that I have the same problem/behavior's as before, I think we can rule out a few things.  I'm just not entirely sure  what the culprit is - coils?  advancer?  something else?  I believe I got the coils from 4-in-1 and they are the "Magna" brand.  Before I'm told that I better go and splurge on Dynatek coils I just wanted to ensure it couldn't be anything else. 

[bryanj]

Not done much modding on the 750 but i think a low tickover with the tuning you have is basically unobtainable

[TheWiredNinja]

I can understand that, but it should still run at low advance and not full advance in order for the bike to run.  I don't have a problem necessarily if I must run idle at higher RPM.

[Don R]

 I'm suspicious of the initial ignition timing, or maybe the cam timing? What is the valve lash with that cam?

[TheWiredNinja]

Oh jeez, you had me really worried with that statement as this is the first time I've rebuilt an engine.  But then I reminded myself that the same sort of idle issue was apparent prior to the rebuild (and that was with all stock internal engine components).

In any case, I went via lobe centers and I got it set to 101.5 degrees versus the 105 degree setting from factory for a 3.5 degree retard in timing (set with valve lash).  Valves were set to 004" intake and 006" exhaust

The only idea I'm running on at the moment is that my coils have degraded.  They were the cheap Magna 5.0ohm coils and they may or may not have seen some electrical mishaps despite them seemingly allowing the bike to rev hard and fast (haven't really ridden the bike yet though).  They certainly are much cheaper than the equivalent Dyna coils... something like $100 Canadian for the pair for Magna versus $300 Canadian for the Dyna - but I suppose that's for another discussion.

The Dyna S ignition was set as per instructions and I also adjusted the rod so it is pretty much trued as per HondaMan's book.  It is rock steady at full advance on both coils.  Battery is topped up and at full charge btw.

[HondaMan]

The 1500 RPM idle could cause fouled plugs more frequently with the OEM carbs, just because that range in those carbs is poorly mixed. It cleans up (going down) by 1200 RPM or so, and also at about 1600 RPM (657A or 7A carbs) or 1750 RPM (657B carbs) with normal cams and pistons.

I can't speak to the other carbs, haven't used them?

I might offer this, from my roadracing days: we often slotted out the screw holes on the points plates so as to add more advance angle overall. This let us set idle timing at something around 12-15 degrees advance for cams like the "stage 3" cams (in today's parlance) which meant they worked from 6500-11500 RPM. These were not cams for LeMans type starts, as the rider had to keep blipping the throttle to keep the engine alive, and we used rear-wheel jack-up type motor starters (with Briggs and Stratton 3 HP engines!) to rear-wheel-start them in the pits. These 750 engines ran much like the 350 Fours and 250 Sixes: the rider had to keep it alive (those bikes had flat-plate carbs with no idle circuits at all) above 2500 RPM. Not streetable...

Overall, that cam likely needs more full advance anyway, given the overlap it has. So, maybe try widening those slots before you start spending precious dollars on things that might leave you right where you are now?

[TheWiredNinja]

Just for clarification - are you suggesting setting the full advance beyond the marks on the timing plate to compensate?  Not entirely sure which position would be 'safe' or too much when going beyond the stock 2nd advance timing mark on the plate.  I believe I still have room for adjustment to advance beyond the standard markings without having to modify the plate effectively extending the range of the timing plate has for adjustment; so I will experiment with that. 

As I have mentioned, observing with a timing light, it's the very moment the advance begins to decrease does the bike cut out but your suggestion is certainly worth a try (if that's what you are in fact suggesting)

[bryanj]

A modified cam and compression will need different timing to original, should have been a data sheet with the cam telling you opening and closing along with checking and running lash plus recommendations for ignition timing.
All the Yoshimura ones came with all that info plus more

[TheWiredNinja]

I was not aware! I have attached the only information given on the 'cam card'.  We may be closing in on the primary issue here after all.  Based in the data, how many degrees beyond the second advance mark should I aim for? 

[TheWiredNinja]

I advanced the plate beyond the maximum full advance marks on the plate and although the bike did seem to like that (at about 1600rpm, advancing the unit caused revs to increase slightly) I did manage to lower the idle a bit to about 1300-1400rpm and then cut out again (assuming the springs rotational forces are just naturally retarding the spark and thereby cutting out again as before).  I advanced it by about the same length as there is spacing between first and second full advance marks to give you an idea - so I'm not sure how many degree's extra that would equate to, nor if that would be too little or too much...

It should be mentioned that it revs nicely otherwise and I'll try to post a video again showing my setup and it's behavior's along with how my vacuum gauges are reading. 

Further notes:  The bike is hard to start when cold.  As soon as I get past stumbling at idle to get a little warmth, it will fire up much easier - I believe this is due to the spark not being at full advance, which the bike likes apparently.

I was told it could be my advancer but I'm not entirely convinced given that it's a fairly new unit from 4-in-1 (model 300 is printed) but with that said, I do still have my original K2 advancer which I may try.  The only other thing I can think of is that my coils may be weak... but obviously I'd like to avoid that expensive at over $300 Canadian for Dynatek coils

Any other suggestions??

[TheWiredNinja]

I've attached a video after syncing the carbs for the most part.  Near the end where my thumb is slightly over the camera lens, I attempt to lower the RPM slightly and you can see it just cuts out. 

Note:  Those "clicking" or "rattling" sounds at idle are typical from Mikuni RS flat slide carbs. 

[enwri]

Do they have pilots and screws? I have no idea, never used those carbs. Seems to stop just when the slides bottom out and stop rattling, isn't that when it's relying solely on the pilot and mixture screws, and getting nothing at all pulling through the throat and past the needle jet?

I can get mine to turn off under 1500-1800 by bottoming out the mixture screws, will still run above that,(not real well) and is hard to start, but can get it to run by raising the slides to let it use the needles and whatever is still leaking through the pilots and screws.

I've recently messed around with mine a bit just experimenting, getting it to idle real low, and can get it to shut off just like yours is doing.. Just stock PDs on a worn old 77 with stock briggs and stratton equivalent cam. (My slides also rattle but that's just because they're old.)

[TheWiredNinja]

Yes, the carbs do have idle jets and screws to adjust for the mixture.  Not entirely sure that is the problem, but I suppose I should try that to see if there are any differences.  My doubt comes from the fact that it just dies out completely versus seemingly to struggle for air/fuel (ie. no popping, stumbling etc) and is behaving the same as with the original carbs installed... and not to mention again that it still must have full advance on, otherwise it will not work.

Anyone have a set of Dynatek coils for sale by chance so I can rule that on variable out? haha

[enwri]

Came back to edit the idle jet size I'm using.. 40 up from 35, not 120, that's the mains.

 Back for a second edit.. Mine stops at 1000 with screws bottomed,
  Idles down to 500 with screws set to 2.5. It's an old loose engine.
   Loses 500 revs Just removing fuel from screws, too small of a idle jet would make an even
     bigger difference to a nice tight engine.

Just went and burned my knuckles messing with it.
I've also got 120 idle jets up from 115.

With the screws bottomed out (No fuel) and lowering the idle until it wont keep going, it gets to about 1000 before it stops. (Doesn't turn off quite like like yours, takes a second to slow and stop, but it's an old sloppy frictionless engine. You'll have more resistance.)

Winding the screws out to 2.5 turns, which is where it seems happiest, and not touching the idle speed adjustment, it  then idles at 1400.

I imagine a nice tight high compression engine with a cam would have plenty more friction and comp. to deal with and would have to spin a bit faster just to keep spinning.

Ignition advance, bumping the idle up when the screws are set to 2.5, it gets to 1500 before the advance moves from static timing and takes over, raising the idle to 2000 with no further movement of the idle adjuster. When checked with a timing light it is at full advance. 

500 revs difference between static and advanced timing.

If it will only idle at 1500, which it can only do with slight throttle opening to get enough fuel, It's keeping the timing advanced.

Any less throttle and it retards and stops.

  DISCLAIMER --  To me, thousands of miles away and with only one short video, it's behaving like it's got blocked idle jets.

[TheWiredNinja]

Hello, thanks for your info and suggestion but here's two earlier video's I made prior to having the Mikuni carbs installed.  Both video's show very similar behaviour with the original K2 Keihin roundtops and at the end of both video's I also try to reduce idle but it just cuts out.  In both instances, I have observed that at the point of cut out when reducing idle, is precisely when the advancer starts to reduce timing from full advance.  For some darn reason, the bike just will not operate on anything but full advance which is why I'm leaning towards a faulty Dyna S, Coils, or something with ignition but I can't figure out what or perhaps something else entirely.

I do not think it's a fuel/air/carb issue at this point given completely different carbs and yet the same results, but I am keeping the suggestions mind as I have yet to fully tune the bike properly and go for a ride.

I am going to follow up with measuring the resistance on coils, secondaries and Dyna S...

[enwri]

Don't mind me, I've just got too much time on my hands so I'm poking my head in again,
I'm pleading my case, I'm invested now.

Like I said Too much time to kill and a long way away.
Here is my story.

Same pipe? Is it just an open collector? Seems the old carbs didn't like it either, and if they were setup with the expected jet sizes but wouldn't idle, new ones set to the same theoretical recipe won't either.

The way the revs don't chop down fast after blipping it, that it takes a few seconds to get back to the revs where it started. Stretched advance springs or the 500s favourite hobby of leaky manifolds and leaning out. (It's not the springs. Are the 500s the ones with the O-rings?)

Too rich an idle mix and it might stall on a quick blip and shutdown, lean usually has to wind it's way back down to idle. Just right chops down quick as the twistgrip and keeps on idling no stumble either way, up or back down. (This works for A series Minis with SU carbs at least.)

 Give an old pilot a massage with a torch cleaning bit and put it in no1 carb, should be able to reach pretty easily. You might be able to hear one cylinder still running longer before it stalls out.

If you don't want to wreck an idle jet, move the air/fuel mix screws to their extreme richest setting and see if it will run slower before it stops. If it makes no difference where the screw is the jet is just wrong and the screw is out of range. Not idling at all usually also means out of range, just much further out. You know which way I'm going to suggest, bigger pilots.

Choking it just right you might get it but that's too rough and uncontrolled, also the slower it gets the less the choke affects it.

I'll be back tomorrow to read about how the voltage drop was shutting down the ignition.

[TheWiredNinja]

Thanks for the input Enwri.  The bike has previously idled at around 1000rpm much earlier on but seems to have degraded over time - and then other issues with the valvetrain had popped up, so it may have been difficult to pinpoint the issue (prior to my rebuild).  With that said, I have completed my electric tests and I found something interesting...

Both coils read 4.9 to 5.1 ohms while the secondaries are both at 27k ohm - which are all correct. 

Upon reading the Dyna S ignition troubleshooting guide, I've found the on their "ohmmeter test" section whereby they want you to place the negative lead on your ohmmeter on the Dyna S plate and the positive lead to the (-) input for the coil (both wires disconnected from coils) and you should get an infinite value.  I got ~22k ohms reading.  This would indicate the pickups may be bad and there is a short.

I contacted Dynatek and they were very adamant that should my readings be correct, the bike should NOT even work at all - but here we are.  So it seems I may be on to something here and I'm going to try and get them to fix or send a replacement. 

Good news is that I won't have to spend $300 on new coils!

[enwri]

I wrote all that and then slipped a "voltage drop" clause in at the end. Trying to cover the "90% carb problems are electrical" and visa versa thing..

 I tried electronic ignition but ended up points and hondaman ign.
Battery went flat enough for the electronic sensor type to stop when stuck in traffic one day. Turned the light off and kicked it and it came back up but points work down to almost nothing. Next best is Hondaman unit and points.

Check the points every few years, haven't had to touch it since.

[TheWiredNinja]

Update:  The Dyna S was returned and tested fine.  Seems that the resistance I was measuring was from the Motogadget M-Unit I have (to which the 12v is supplied).  Bottom line is ignition works but the issue remains.

I went ahead and took out the other single spring on the advance mechanism and it starts right up!  I can even get it to idle around 1100 rpm without much issue.  The problem is that the bike is undoubtedly at full advance all the time now and I'm not sure why it must be this way in order for it work like a normal bike.

It does seem to rev up and ride just fine now, but upon revving-down it isn't as crisp as I'd like to given that the advance is always at full.  At least I can continue to fine tune the bike and perhaps getting working as best as it can, but if anyone has any other suggestions as to why this is so dependent on full advance, please let me know!  Perhaps more loose advance springs would be a good compromise for this situation?

 I'll post another updated video to show you guys what it's like now.

[Tracksnblades1]

Have  you verify your advancer timing is accurate.

It has a pin that indexes in the crankshaft…

This pin can be sheared off when trying to turn over an 836 with the advancer nut….

If this pin is sheared and your advancer has moved in relation to the dowel pin hole, your timing light means nothing…

Additionally, As Bryan J and Don R may be hinting, you should know your opening and closing event’s timing of your camshaft. Especially if you degreeed your cam to 101.5* lobe center instead of 105*.. I’m really worried you believe that 101.5 is 3.5* retared….🤔

Did your degree wheel positive stop TDC match your advancer’s TDC …? 🤔

[TheWiredNinja]

How can I verify if advancer timing is accurate? 

I have trued the shaft recently as per HondaMan's book and the advancer unit with the pin does seem to be lodged in the pin hole without problem.  The two weights/levers are free to move and well lubricated (in fact, it's a fairly new unit, albeit a newer '300' model than the original - which I still have).

The 101.5 lobe center was as close as I could get it with my adjustable sprocket - I also took measurements of BTDC and ATDC etc. and they were fairly close.  I don't have the numbers at the moment, but I believe they came up around 3 degree's retarded from the cam card numbers.

The true TDC did not match the advancer unit's TDC.  I measured true TDC and it came up just passed the "F" mark on the advancer.  I did try to set the timing so that at full advance, the timing was set passed the second full advance mark by an equivalent amount.  The bike still didn't like running at anything less than the full advance as described above, and would cut out as soon as the timing would shift downwards.

It should also be noted that I took the bike for a test ride and although it needs a little tuning, it is VERY quick in the powerband where the tuning seems right (needs larger jetting at full throttle and slight tweaking at mid throttle, low rpm).  This is all with the advance springs removed.  It seems to be mechanically sound otherwise...

[HondaMan]

I just now got my computer to download and open that 295 cam card file you have (above). That's a lot of early intake valve degrees(!).

What's happening (physically) is this: the intake airflow at low engine speeds is nil. The piston is pushing the air/fuel mix back toward the carb with that early-open intake valve, so not much of it is still in the cylinder at low engine speeds. This kills off the engine's idle capability until enough mixture is left to burn it for a cycle, which sounds like it is about 1500+ RPM. For racing cams, that's not unusual.

The full-advance spark setting may be needed to run below the point where the new air-fuel charge is starting to make it into the cylinder (i.e., around 2000 RPM with a cam like this), but there may also be a need to advance further with RPM: the guys who were making the 12k and 14k (one was 16k) RPM mini-car engines out of this 750 were running full advances in the 45+ degree range. This would correspond (roughly) to having the idle timing setting nearly halfway thru the indicated range so it could advance beyond the upper marks at about the time the cam is "coming on". With 19 degrees BTDC intake opening, my guess is for this cam's starting point to be somewhere around 6500 RPM?

So, what I might suggest is this: drill new (or make really long) slots such that the 'idle' setting of the spark starts at about 20-25 degrees. This should let the full advance timing be around 50-55 degrees. Then put the spark advancer's springs back in...here's an example of what I'm attempting to explain: the guys who made mini-car engines out of these were routinely running 14k redlines with points. There were 8 guys using the Honda engines, I knew 4 of them, and one of these was using doubled-up springs on his points (beautifully hand-welded together by him), and this one guy was running to 16k RPM in his car. One of them was running 12k RPM, and he was using stock points (Hitachi and ND). While I was not privy to their 'tuning secrets' entirely, looking at their setups showed things like very long slots in the timing plates (made on their mills in their barns) and other-than-OEM condensors, usually being the ceramic electronic type, RTV'd to the backplates. The advancers were modified stock units, the one I saw in-hand was an AD125 Hitachi unit as found in late K1 and most of the K2 750s. Their advancer weights were lightened and the stops on the advancers were cut thinner and then bent outward to make more advance: one had the stops cut clean off (he was the 16k RPM guy) for apparently much more total advance. His was a complex advancer, though, with multiple camming plates for an "S" profile that retarded the spark between 14.5K and 15K and then let it go again: he ran up to 16k RPM, although it wasn't a smooth, linear transition  above 14K RPM.

All this is a long-winded way of saying, "You may have to set your idle timing to be almost full advance." Then let the advancer weights control further advance as the speeds rise. You should be able to hear ping (knock) if it starts happening: if so, you could then add 'stops' on the limiter stops like maybe O-rings of varying thicknesses (or something similar) to prevent the weights from moving further outward, thus delivering less full advance.

Typically (as the Ford 427 SOHC engines showed) this advancing rate should be linear (as springs are) and might not have an upper limit of total degrees advance, although the TEC advancer's stops will limit that upper number. Another engine's example (from this Ford engine of reknown) is the distributors that had 2 different springs in them, one with long oval loops on the ends and one that looked normal: at low RPM (below 3000) the spark advance was controlled with the normal-looking spring, but as the engine passed above 3000 RPM the other spring came into play as the advancer's mounts used up the slack in the second spring's loops, and a slower curve-per-RPM came into play. Those V-8 monsters turned 8500+ RPM with the HP still climbing past 750 with a pair of 4-bbl Holley carbs set for progressive opening of 2, then 4, then 6, then 8 barrels feeding one intake manifold. In those tests, the dyno ran out of capability first! Ford took some of this tech to the street in my 1967 LTD with the famous 2-bbl 390H engine with zero deck-height pistons: its distributor was similarly set up at lower RPM to have 1 spring with long loops on it and the other (lighter) one normal: it ran from 800-1500 RPM with the primary spring advancing quickly for good fuel MPG in city traffic with good engine response, while the 2nd spring altered the slope (slower) of advance above 2000 RPM: first, it held the advance at 18 degrees from 1500-2000 RPM and then more slowly added degrees above that to 45 degrees full advance at 4850 RPM (which was 115 MPH with the tall 2.75:1 differential in that car) when the limits of the advancer plate stopped any more advance. That car could easily bury the 120 MPH speedometer, which had a stopping pin to prevent the indicator needle from hitting the side of the display! I loved that car...it got 18 MPG hiway, too.

[TheWiredNinja]

HondaMan, thank you and sorry for the delay in getting back.  I think you described it accurately as the carbs would "spit back" pretty strongly at low RPM without the full advance, possibly a result of what you described.  When I bought the this cam, I was under the impression that it wasn't all that aggressive and in fact, recommended for this setup.  I wasn't aware of the additional tuning issues that would come as a result (even though I don't necessarily mind the additional "inconveniences" of higher RPM and advance timing quirks)

As promised, I made another video showing its behaviour.  I'm still working on tuning and it will need a richer needer clip position and certainly a larger main jet (currently 125) with these Mikuni RS34's.  As you may notice, the low RPM rev-down is much better after a Bunson Color-Tune to set the idle mixture properly.  They were initially too lean and I made the flame a yellow/blue versus solid blue color.  One thing that initially confused me with the RS34's is that turning the mixture screw OUT = RICHER and turning IN = LEANER.  The opposites of the standard Keihin rountop carbs. 

last note:  It was cold weather and the battery was a little low, so it wasn't as crisp as noticed before, but it's an improvement comparing from previous video's.

[PeWe]

RS34 has fuel screws, CB750 stock round tops, airscrews.

A DP295 will run fine with stock ignition setting if done correctly.

I use TMR32, also with fuel screws. Outwards, more fuel. I have dyno/afr charts verifying that. A bunch of sooty plugs too.

I have used an  RC295 profile.
Timed it with 0 lash.
Time with running lash recommended, but I want to see cam card numbers or close.
Lash often 0.004" (0.10mm)
I use 0.006" on Ex (0.15mm)
I use metrec feeler gauges, so 0.10 and 0.15mm.
Some cams slightly more 0.005".

RC315 whopping 0.012" (0.3mm)
Tested less and got lower power, lower torque when twisting. (Test ride, butt dyno.)

I tightened valve adjuster screw until I saw valve moved down ca 0.02mm to be sure. This when rocker arm rested on base circle.

I had also verified the true TDC so 0 on timing wheel was correct.
This timing when my K6 had 836cc:
@0 lash, open/close at 1mm (0.04") lift
IN: 25/55.
Lift 9.98mm(.393")
LC: 105

EX: 55.5/22
Lift: 9.22mm (0.363")
LC: 106.75

Retarded or advanced?
(25-22)/2
[in open-ex closed]
1.5* advanced. (Found method explained on this forum)

This cam has almost EX as inverted values of IN.
Many cams are like that.


I have used Pamco electronic igntion, Stock points, later with Hondaman module and Dyna-S.

All with cut advancer springs to make sure ignition does not advance too early wich my K6 did way too much 2013.

I have also checked where advancer T match case mark when pistons are at TDC. Both piston stop and degree wheel and measured without head.

If advancer has a play when the small nut is not tightened. Correct at most counter clockwise position.
My CB750 K2 too.

Spot on mark have worked fine for me.

I have tested advancing and retarding when bike was on dyno. Spot on was best, not more advanced.
I marked ign plate with marker pen, rotated ca 2mm on the outer edge.

This with DP315, I think I did that later with RC295.
All these with 1005cc.

DP315 and RC295 idled really nice when carbs where OK in that area.

Bike got later a Megacycle 125-75 and idles really fine despite higher compression. It runs harder. 

Carbs are Mikuni TMR32. Idle is a pain to adjust with thin screwdriver between pod 2-3.  Small hands needed.

It is OK when really warm, ca 1200rpm which makes take offs easier and throttle offs not that hard braking.
It idles sometimes around 1000rpm without issues. More care at take offs needed.

I have an excel file where I have written down the cams with timing values, cam cards too.

[Tracksnblades1]

RS34 has fuel screws, CB750 stock round tops, airscrews.

A DP295 will run fine with stock ignition setting if done correctly.

I use TMR32, also with fuel screws. Outwards, more fuel. I have dyno/afr charts verifying that. A bunch of sooty plugs too.

I have used an  RC295 profile.
Timed it with 0 lash.
Time with running lash recommended, but I want to see cam card numbers or close.
Lash often 0.004" (0.10mm)
I use 0.006" on Ex (0.15mm)
I use metrec feeler gauges, so 0.10 and 0.15mm.
Some cams slightly more 0.005".

RC315 whopping 0.012" (0.3mm)
Tested less and got lower power, lower torque when twisting. (Test ride, butt dyno.)

I tightened valve adjuster screw until I saw valve moved down ca 0.02mm to be sure. This when rocker arm rested on base circle.

I had also verified the true TDC so 0 on timing wheel was correct.
This timing when my K6 had 836cc:
@0 lash, open/close at 1mm (0.04") lift
IN: 25/55.
Lift 9.98mm(.393")
LC: 105

EX: 55.5/22
Lift: 9.22mm (0.363")
LC: 106.75
Retarded or advanced?
(25-22)/2
[in open-ex closed]
1.5* advanced. (Method explained on this forum)

This cam has almost EX as inverted values of IN.
Many cams are like that.


I have used Pamco electronic igntion, Stock points, later with Hondaman module and Dyna-S.

All with cut advancer springs to make sure ignition does not advance too early wich my K6 did way too much 2013.

I have also checked where advancer T match case mark when pistons are at TDC. Both piston stop and degree wheel and measured without head.

If advancer has a play when the small nut is not tightened. Correct at most counter clockwise position.
My CB750 K2 too.

Spot on mark have worked fine for me.

I have tested advancing and retarding when bike was on dyno. Spot on was best, not more advanced.
I marked ign plate with marker pen, rotated ca 2mm on the outer edge.

This with DP315, I think I did that later with RC295.
All these with 1005cc.

DP315 and RC295 idled really nice when carbs where OK in that area.

Bike got later a Megacycle 125-75 and idles really fine despite higher compression. It runs harder. 

Carbs are Mikuni TMR32. Idle is a pain to adjust with thin screwdriver between pod 2-3.  Small hands needed.

It is OK when really warm, ca 1200rpm which makes take offs easier and throttle offs not that hard braking.
It idles sometimes around 1000rpm without issues. More care at take offs needed.

I have an excel file where I have written down the cams with timing values, cam cards too.

“Timing” is everything….as well as camshafts…

Still wondering how a 105* lobe center cam installed at 101.5 intake lobe centerline  is 3.5 degrees “retarded”…?
To prevent the endless circling, It would be to everyone’s advantage to know exactly what the actual ignition and installed cam timing is..

https://www.austincc.edu/wkibbe/camtheory.htm#:~:text=I%20mentioned%20earlier%20that%20advancing,earlier%20during%20the%20intake%20stroke.

Oh jeez, you had me really worried with that statement as this is the first time I've rebuilt an engine.  But then I reminded myself that the same sort of idle issue was apparent prior to the rebuild (and that was with all stock internal engine components).

In any case, I went via lobe centers and I got it set to 101.5 degrees versus the 105 degree setting from factory for a 3.5 degree retard in timing (set with valve lash).  Valves were set to 004" intake and 006" exhaust

The only idea I'm running on at the moment is that my coils have degraded.  They were the cheap Magna 5.0ohm coils and they may or may not have seen some electrical mishaps despite them seemingly allowing the bike to rev hard and fast (haven't really ridden the bike yet though).  They certainly are much cheaper than the equivalent Dyna coils... something like $100 Canadian for the pair for Magna versus $300 Canadian for the Dyna - but I suppose that's for another discussion.

The Dyna S ignition was set as per instructions and I also adjusted the rod so it is pretty much trued as per HondaMan's book.  It is rock steady at full advance on both coils.  Battery is topped up and at full charge btw.