Topic: Points plate at end of adjustment

[JohnK3]

I recently acquired a low mileage 1971 CB750 in non running condition (https://bringatrailer.com/listing/1971-honda-cb750-6/). After rebuilding and syncing the carbs,  I noticed that #2 & #3 cylinders have noticeably weaker exhaust pulses as felt at the exhaust outlet. A pyrometer on the exhaust pipes close to the head shows temps at 180, 90, 130, and 175 degrees F, measuring #1 thru #4.  All cylinders have good compression.

A look at the points showed that the #2 & 3 point gap were noticeably wider than #1 & 4. So, I set both points to .014 and while I was at it, I checked the timing.  It was way off, even though the the the points plate was approximately in the middle of it's adjustment range.

I had to rotate the points plate almost all of the way counter clockwise to get the F mark aligned with the points opening as measured by an ohm meter. I also used a timing light (cranking only, not running)  to confirm timing.

It seems unlikely that I have this correct with the timing plate at the extreme end of it's adjustment range.

BTW, I have not ridden the bike. All of my work has been done with it on it's center stand. I live in Arizona, so road testing is generally not a problem, weather wise.

Any idea of where to go from here?

[DaveBarbier]

The FAQ has a write up on what to do if you run out of adjustment range on your points plate. From member TwoTired.

http://forums.sohc4.net/index.php/topic,91211.0.html

[PeWe]

Advancer springs too weak, stretched. Advancer rotor will then have a play clockwise until springs kicks in.

Remove advancer and cut both springs 1/2 wound, reshape cut end with pliers. Redo the timing and see it will work.

I have done both my CB750 this way. Electronic ignition or points, same need.

[bryanj]

If points are worn plate adjustment can be at end. Also when you move the plate the gap on points will alter

[scottly]

I had to rotate the points plate almost all of the way counter clockwise to get the F mark aligned with the points opening as measured by an ohm meter. I also used a timing light (cranking only, not running)  to confirm timing.

If the timing checks OK with a strobe for both sets of points, move on.

[HondaMan]

Look closely at the points, see if they have a tiny 3-leaf-clover-like symbol on them. If so, they are Daiichi points. These are slightly "off" in geometry, but will run fine if you can reach the timing marks with them, with gaps in the range of 0.012"-0.016". They are cheap points (and their condensors are big trouble), but they can run OK.

[Deltarider]

Curious. Never had that problem. I stick to genuine Honda Parts. In my case TEC. Have a look at the pic below if you like. This is more or less what you will see, if you adjust as prescribed. On my CB500 it's the position plates and breakers have been in all their lives. Almost smack in the middle. When this pic was shot, the breakerpoints had seen over 55.000 kms. Did I already mention these are genuine Honda Parts? 

[JohnK3]

I've been using the F mark for initial timing.  Should I be using the T mark?

[Deltarider]

No, the "T" mark indicates TDC (top dead centre). That one is for checking the valves. The "F" mark has to align for a correct static timing, like you did. Below a pic of the CB500/550 advancer. Yours will be somewhat different, but the idea is the same.

[evinrude7]

Advancer springs too weak, stretched. Advancer rotor will then have a play clockwise until springs kicks in.

Remove advancer and cut both springs 1/2 wound, reshape cut end with pliers. Redo the timing and see it will work.

I have done both my CB750 this way. Electronic ignition or points, same need.

not to hijack here but Per, my plate isn't out of adjustment room but i'm towards that direction.  with a light on the viewing hole, i don't go past advance when rev'd.  in your opinion since you seem to be a big proponent of clipping 1/2 a spring coil, would it hurt to cut mine?  what if any would it improve? 

[PeWe]

My CB750 K6 had very sloppy springs 2013, ignition not possible to set when full advance kicked in way too early.

Found Hondaman's old post about it and cut the springs as he described and problem solved.
F set correct at idle, full advance around 2600rpm. This was initially with Pamco, followed by Dyna-S, TEC points and now Dyna-S again that has its own advancer also with cut springs and avoid struggling with the stock rotor off- Dyna rotor on.

Then my CB750 K2 build with TEC points, advancer not that sloppy. I could not get F correct at idle, just 1-2mm before the mark. I could not turn plate enough clockwise despite high setting of points (dwell @ 23degrees).

Out with advancer, cut the springs 1/2 wound on each. Now possible to get F to match case mark at idle. Harder sorings delay the advance.

Full advance at around 2600 rpm.

Both my bikes runs fine.

Even Dyna-S manual describe to set ignition so full advance happen at 2500 rpm! Just skip the important idle and low rpm.
They know the "problem" and ignore it.
Dyna-S manual is more like a fault tracing guide for a failing unit than an installation guide.

I prefer to get ignition correct at idle, important take-off behaviour not let ignition advance too much too early.

[DaveBarbier]

Advancer springs too weak, stretched. Advancer rotor will then have a play clockwise until springs kicks in.

Remove advancer and cut both springs 1/2 wound, reshape cut end with pliers. Redo the timing and see it will work.

I have done both my CB750 this way. Electronic ignition or points, same need.

not to hijack here but Per, my plate isn't out of adjustment room but i'm towards that direction.  with a light on the viewing hole, i don't go past advance when rev'd.  in your opinion since you seem to be a big proponent of clipping 1/2 a spring coil, would it hurt to cut mine?  what if any would it improve?

Clipping the advance springs is a fix for old worn out springs. They don’t hold the advance mechanism back as much as they used to so the timing actually goes passed the advance marks. Clipping the spring essentially makes the spring a little tighter so it holds it back more. In your situation you want to make the advance go farther so clipping would do the opposite of what you want. I would look into shimming your points plate or setting your dwell differently. Of course this assumes the rest of the parts on the plate are set correctly and not worn.

[PeWe]

All points new TEC, Dyna-S correct too.  Plates sit tight in case.
I guess I'm more to get it exact than others that does not care if ignition is a little bit too advanced at idle.

Struggling with this is the reason why so many really dislikes points. Use Dyna-S, follow their instruction that bypass the spring issues by setting ignition at full advance at 2500 rpm and ride.

One more thing. I have also verified the real TDC on both cranks with advancer so I know how the advancer play will do and how to be sure that T is at correct mark at TDC, F will follow.
Both with head off,  and later piston stop with head on at different cam timing sessions.
My K6 had really worn springs.

My K2 not so I have still not solved the mystery of max clockwise position of plate, point gaps at max, cut springs made F to finally align with case mark at idle. Max advance OK. Ignition colorisation on sparkplugs ground straps exact in the corner too. 56whp on dyno.

Cut springs also make a more stable ignition while checking it with timing lamp. Marks look sharp, almost as engine standing still. Separate battery feeding the timing lamp helps too.

Cut the springs as I have done, nothing bad, only good

[DesertKyorugi]

I recently acquired a low mileage 1971 CB750 in non running condition (https://bringatrailer.com/listing/1971-honda-cb750-6/). After rebuilding and syncing the carbs,  I noticed that #2 & #3 cylinders have noticeably weaker exhaust pulses as felt at the exhaust outlet. A pyrometer on the exhaust pipes close to the head shows temps at 180, 90, 130, and 175 degrees F, measuring #1 thru #4.  All cylinders have good compression.

A look at the points showed that the #2 & 3 point gap were noticeably wider than #1 & 4. So, I set both points to .014 and while I was at it, I checked the timing.  It was way off, even though the the the points plate was approximately in the middle of it's adjustment range.

I had to rotate the points plate almost all of the way counter clockwise to get the F mark aligned with the points opening as measured by an ohm meter. I also used a timing light (cranking only, not running)  to confirm timing.

It seems unlikely that I have this correct with the timing plate at the extreme end of it's adjustment range.

BTW, I have not ridden the bike. All of my work has been done with it on it's center stand. I live in Arizona, so road testing is generally not a problem, weather wise.

Any idea of where to go from here?

I am having similar issues with my K1. I can get the 1-4 gap and timing perfect but 2-3 would be out of range and can't hit the timing F mark. I was playing with moving the timing plate(s) around but then Thanksgiving and Christmas busy time interrupted the fiddling. I guess I will have to start over fresh and see which movement directions affects which timing adjustments.

[scottly]

I had to rotate the points plate almost all of the way counter clockwise to get the F mark aligned with the points opening as measured by an ohm meter. I also used a timing light (cranking only, not running)  to confirm timing.

"almost" is the key word here. As long as you can set the timing within the range of the points plate travel, you are good. Minor variations in the way you have set the gap will affect the final position of the plate, even within the stock range of .012"-.016". Also, do not bother trying to set the timing by rotating the point plate until the meter shows the points have opened, as it changes as soon as you tighten the screws. Instead, turn the motor with the kick starter, then loosen the plate, adjust in the direction needed, snug the plate, and turn the motor over one full turn to check again. Still off? Repeat as required. Once you are satisfied, give the plate screws a final tightening and put the points cover on.

[PeWe]

Another thing with points. Do not give up. Point gaps correct. If plate need to be adjusted max clockwise and more, make sure gaps are at max which will delay it.
Typical is the need to fiddle with adjustments and suddenly it will work! I have seen the need to be rotated more than max clockwise to suddenly sit almost middle of the plate adj area.

Point 2:3 has been the one with most need to readjust since its plate can move, not only sideways when adjusting.

I used a test screwdriver back in the days. Points gapped, connect screwdriver on point and plate when ign is on. Rotate crank when it lit, lamp should come off when F is aligned to case mark. With this method you will not see any problems but maybe not that exact as possible.

Points are a fun detail on these bikes. And very reliable.

[Deltarider]

Here what has always worked for me. Shown below are the CB500/550 ignition parts from behind the cover.
Normally adjusting the ignition timing, if needed at all (!), can be limited to simply readjusting the breaker points gap. Period. That's how the Honda mechanics did it back then. Again... if needed. It makes sense: the plates are for ever firmly held in position by their screws, so an eventual off timing originates only where there is wear in play. That's at the breakerpoints: could be pitting, could be the fiber followers. With genuine Honda parts and a slightly lubed felt there will not be much wear.
Most of you have manuals and in them you will always find the full procedure prescribed. This is to cover that special event when things were taken apart completely. I have done this twice (in 40 years!), the first time out of curiosity and the second time to service the advancer. Not that it was needed; I did it anyway, out of precaution. 
Many times you will read here that you are not to use the 'special washer' (Hondaspeak) for cranking, unless sparkplugs have been removed. Maybe this is advisable for other CB models, on CB500s and CB550s I never had a problem. Can you damage the hexagon? Sure, you can. You can round it. But it isn't there for nothing. Just do it the right way. If you take care, you can do it with a good quality adjustable wrench like an original Bahco. I've done it multiple times when on the road and I still have the original hexagon. In the garage I prefer a 23mm socket on a T-handle however. With the bike on the side stand, leaning over a bit, I find it quite doable to exercise pressure to keep the socket in place, against the hexagon. The extension bar is there, since my bike has crash bars fitted. Many of you can do without. By using a T-handle there's little risk rounding the heaxagon and you can turn the crank clockwise no prob. Ofcourse it's best done when the engine is cold. So there's no urgent need to remove the plugs and, frankly, I estimate the risk something goes wrong removing the plugs and then fitting them again higher than damaging that 23mm hexagon.
Let's assume you couldn't fight your curiosity and have taken things apart (see pic) and now it's time to reassemble. Here's a tip. From an old credit card, cut two corners; two little pieces that you slide between the breakerpoints. On the right you see one such piece on the floor. The second one is already in between the left breakerpoints. These pieces will make reassembly much easier: you don't have to fight the breakers springload when you fit the plate assembly over the advancer cam. The pieces have a thickness of around 0,5 mm and that is enough to make it easy to fasten the central 6mm bolt correctly: right in the middle of the 'special washer'. Provided you have genuine Honda parts, you can safely centrate the plate by fastening the three crossheads. Remove the plastic pieces. Done. If the ignition timing was OK or close before, you have ofcourse made a little scratch from the ignition plate to the crankcase to facilitate a precise aligning or at least have some reference. Success!

[HondaMan]

I recently acquired a low mileage 1971 CB750 in non running condition (https://bringatrailer.com/listing/1971-honda-cb750-6/). After rebuilding and syncing the carbs,  I noticed that #2 & #3 cylinders have noticeably weaker exhaust pulses as felt at the exhaust outlet. A pyrometer on the exhaust pipes close to the head shows temps at 180, 90, 130, and 175 degrees F, measuring #1 thru #4.  All cylinders have good compression.

A look at the points showed that the #2 & 3 point gap were noticeably wider than #1 & 4. So, I set both points to .014 and while I was at it, I checked the timing.  It was way off, even though the the the points plate was approximately in the middle of it's adjustment range.

I had to rotate the points plate almost all of the way counter clockwise to get the F mark aligned with the points opening as measured by an ohm meter. I also used a timing light (cranking only, not running)  to confirm timing.

It seems unlikely that I have this correct with the timing plate at the extreme end of it's adjustment range.

BTW, I have not ridden the bike. All of my work has been done with it on it's center stand. I live in Arizona, so road testing is generally not a problem, weather wise.

Any idea of where to go from here?

I am having similar issues with my K1. I can get the 1-4 gap and timing perfect but 2-3 would be out of range and can't hit the timing F mark. I was playing with moving the timing plate(s) around but then Thanksgiving and Christmas busy time interrupted the fiddling. I guess I will have to start over fresh and see which movement directions affects which timing adjustments.

This one is possibly (likely) a different situation: this is the symptom of a bent advancer shaft. It is very common on the 750, caused by pulling the crankshaft CCW direction with the sparkplugs still in the engine. The location of the dowel on the end of the crankshaft, with the fulcrum angle of a long wrench on the big nut, is just right to bend the shaft.

The advancer must come off (and the points plate) and a dial indicator used to help you re-straighten the shaft. I lock 2 6mm nuts together on the shaft to tap (firmly) with a ballpeen hammer to straighten them back within 0.002", at which point the "jitter" of the timing marks (especially the 2-3 marks) and the wide variance between the points gaps finally goes away. I do it to nearly every 750 I rebuild, anymore: it seems most of them are bent, probably from "static timing" using a 12v bulb and pulling the crank back-and-forth while wathing for the "F" marks to pass slowly by.

Timing lights are much easier on these bikes...

[JohnK3]

Update on my '71 CB750:
(Full disclosure: I'm a newbie mechanic, but determined to see this through)
I have reset my points to .013, and triple checked my work: 014 is too tight, .012 feels too loose, .013 feels just right (Cue the 3 Little Bears).
I have set the static timing, and confirmed it with an inductive timing light, as well as the timing advance at 3,000 RPM.
The inductive timing light lights up on all 4 spark plug leads.
All spark plugs sparked when removed, hooked up, and laid on the engine to ground them.
The "clear tube" test showed carb float bowl levels to be approximately even between all carbs.
I'm still seeing significantly lower temps on # 2 & 3 exhaust pipes as well as substantially weaker exhaust pulses as felt by a hand placed by the exhaust tips.
I'm thinking that my rebuilding of the carbs was inadequate. Because they were so polished and shiny, I was hesitant to immerse them in that caustic carb cleaner solution we use at our boat dealership.
I'd appreciate any thoughts on how to proceed from here. 

[754]

 Plus one on check the shaft.
 The big hex nut.... I use the 2 hole toolkit wrench that comes with the bike, plus the extenion squashed tube.
 It is thin, very little bevel ,and will turn it with plugs in. I suppose taking outer 2 plugs out would help.
 Now consider this , most sockets are deeper than this wrench, most wrenches are thicker than the factory wrench.
 Because of that  they have more lead in taper , for easier getting it on the nut. . THIS IS THE REASON, the thin nut at end of crank can get rounded off easily, if you have proper engagement, it won't be a problem..

[JohnK3]

From Hondman:
This one is possibly (likely) a different situation: this is the symptom of a bent advancer shaft. It is very common on the 750, caused by pulling the crankshaft CCW direction with the sparkplugs still in the engine. The location of the dowel on the end of the crankshaft, with the fulcrum angle of a long wrench on the big nut, is just right to bend the shaft.

The advancer must come off (and the points plate) and a dial indicator used to help you re-straighten the shaft. I lock 2 6mm nuts together on the shaft to tap (firmly) with a ballpeen hammer to straighten them back within 0.002", at which point the "jitter" of the timing marks (especially the 2-3 marks) and the wide variance between the points gaps finally goes away. I do it to nearly every 750 I rebuild, anymore: it seems most of them are bent, probably from "static timing" using a 12v bulb and pulling the crank back-and-forth while wathing for the "F" marks to pass slowly by.

Timing lights are much easier on these bikes...

Hondaman,
Are you removing the advancer shaft, or straightening it in place?

[PeWe]

Must be easiest as it sit in crank. Remove advancer, dial indicator against stud, rotate crank without plugs in. Use kickstarter carefully by hand in small steps.

Use a metal hammer to hammer where it wiggle sideways. Hammer lightly, it will be bent really easy.
Check again with dial indicator while rotating crank.

I use kickstarter more nowadays instead of a 23mm wrench. The advancer pin can wear the hole in crank or pin causing a lash that will affect how T and F aligns with case mark.

Advancer fully counterclockwise  correct TDC on both my bikes.

If setting advancer max clockwise T and F will align too early. The corresponding case mark should then be later to match. I have seen 2-3mm, verified with degree wheel and piston stop.
Also with dial indicator with head measure piston dome.

Check real TDC the first thing to verify when timing a cam with adjustable sprocket.

[754]

 ACTUALLY USE a wooden dowel or soft punch against advanced nut, then hit that with the hammer...

[JohnK3]

A dial indicator showed .020 runout on the advance shaft. Many thanks to Hondaman, Pe We, and 754. I'll post results when I get it taken care of. Any reason other than cost to replace the shaft rather than straighten?

[PeWe]

Yamiya750.com sell new stud with o-ring or separate.
Much easier to bang the old one straight.
If really bent as after an accident or dropping the crank, new can be actual. Or if buying a crank without it.