Author Topic: Ignition Analysis: Honda's coils  (Read 44391 times)

0 Members and 1 Guest are viewing this topic.

Offline 754

  • Really Old Timer ...
  • *******
  • Posts: 28,502
Re: Ignition Analysis: Honda's coils
« Reply #50 on: March 06, 2008, 08:16:05 am »
I sincerely hope that everyone on here gets to ride with other years of the same model & perhaps hopped up ones, & actually gets to trade bikes and get to ride them a bit..

could be an eye-opener.....................
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline Helo229

  • Enthusiast
  • **
  • Posts: 108
Re: Ignition Analysis: Honda's coils
« Reply #51 on: March 16, 2008, 03:52:19 pm »
Just out of curiousity, doesn't DYNA recommend switching the stock coils out for their 3ohm coils? And if you're going to use points to use 5ohm? I'm a ways off from replacing mine, but it is something I'm looking to do in the future.

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 10,319
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: Ignition Analysis: Honda's coils
« Reply #52 on: March 16, 2008, 08:32:29 pm »
Just out of curiousity, doesn't DYNA recommend switching the stock coils out for their 3ohm coils? And if you're going to use points to use 5ohm? I'm a ways off from replacing mine, but it is something I'm looking to do in the future.

Dyna's recommendation is: "Use only coils that are within 10% of the stock ohms of your bike." Honda SOHC4 coils are about 4.5 ohms, so anything less than 4.1 ohms is too low, by that rule. You could go up to 5 ohms with no problem. Adding the resistors restores the "rule".
The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline nowayjosey

  • Jose Moraes
  • Full Member
  • *
  • Posts: 5
  • This is my baby
Re: Ignition Analysis: Honda's coils
« Reply #53 on: March 20, 2008, 11:33:00 am »
HI Hondaman,

Once more I followed your recommendations with good results. In the "High Gear Wall" message you posted, you suggested to increase the sparking plug gap. I am using now 0.9 mm (together with the Dyna ignition) and it improved the response of the bike in mid and high rpms once again. I will try 1.2 mm gap as well.

The next step will be to use a K&N air filter (NH-0100). I will keep you posted.

Many thanks again for your hints !

Strange. I wonder if issues like this can be traced to certain years. My K8 is all stock engine-wise and pretty much everything else except for my dyna S. I do not have the difficulties with rpms of speed or anything like that. I have not done the ton but that is by choice as I have kids and would rather see them grow then see a ton.

My coils are original too only change is the plug caps. I also have not done any real work to my wiring either. I wonder if later years have more powerful systems?

Yeah, I'm slowin' down...that's why my 17-tooth front sprocket is OK now (only...126 MPH at redline in 5th).
Here's how you can "test" the scenario: we used to call it "the tall gear wall", and it was noticeable from the K2 onward, in increasingly worse degrees to the K5: on a warm summer day, get into high gear at 40-45 MPH, then just roll on the throttle and see how fast it will go. Frequently, they would "hit the tall wall" at about 80-90 MPH and stop accelerating. If you then dropped into 4th and poured it on, they would break to the ton, and then would pull 5th to the top. On real hot (90+) days, it sometimes would not pull past the 4th gear's top speed, but would slow down in 5th (CB500/550 suffers this more often).

The problem is 3-fold, really: it's a subtle change in efficiencies from the K1 onward, starting with the pipes. To keep the plugs clean in slow driving, Honda had to lean out the (very) rich open-pipe mix of the earlier open pipes for the newer HM341 pipes. Rich mixtures fire much easier, and burn longer, at higher RPM (as any cafe' or RR rider has learned) with any given spark. With a leaner mix, the engine needs a longer (or wider-gapped) spark to ignite more of the flamefront to get it all to burn in time. If you then throw in the taller gearing of the K2-later bikes (18T front sprocket instead of 17T) and add the 2-row output bearing on the countershaft, the engine pressures rise enough to stall the flamefront in the leaner mixtures at wider throttle openings (2/3-3/4) and lower engine speeds (typically about 6500 RPM in 5th gear). This is where it appears: the roll-on creates a lean mixture just as the torque requirement rises, and the mix isn't rich enough to carry the cooler flame through the whole stroke, so it "stalls" at building torque.

If you add a wider plug gap and the voltage to jump it, a wider flamefront appears, which burns faster, hotter, and more efficiently. You can also make a longer spark, which the Honda coils are compared to the Dyna, to try to ignite a wider swath of the moving mixture. The Honda coils do have their limits, particularly if the points are burned somewhat or are cheapies (tiny mating faces make poor instantaneous peak currents), so the Dyna S units appear to prolong the "new points feeling" better after 1000 miles than did points. The Dyna coils discharge faster, so they need a wider plug gap to get that wider flamefront, and they have the volts to do just that.

The later carbs (late K4 and on) showed some attempts to improve the richness at higher RPMs to deal with this issue. Although fairly rare, some carbs came equipped with "lifting collars" like the ones used on 2-stroke big-bore port-timed engines (these carbs also have non-changeable jets!). These increased the suction on the needle jet at 2/3 throttle & upward, distinctly returning the "K0 feeling". I saw some of these just as I was leaving Illinois in 1974, on a pair of K4 bikes from California that I was tuning for some passers-by. These mods did, however, lower the MPG, to be like the K0's 35 MPG hiway numbers (the K4 was approaching 50 MPG without them).

So, for any given stock bike, improving the coils' performance turns the key to improved passing with No Fear on mountain roads. The "HM" Transistorized ignition does this by pretending to be perfect points, forever, through a little built-in electronic trickery. The Dyna S does it by being better than 1000-mile old points. The Dyna 3-ohm coils (with or without resistors) do it by heating the plug tips more if stock-gapped, or by widening the flamefront more with bigger (.050") gaps. The Dyna III does it by stretching the OFF time of the Dyna S-like trigger, to simulate the points' healthier dwell times. Any of these methods help fell the "tall gear wall". Richer jetting helps fell the wall, too, but with stock HM341 pipes, you'll pay for it in dirty plugs, unless you use higher voltage coils to keep them heated and burned clean.

One way to modify the carbs to get past "the wall" while keeping the in-town plugs cleaner is to open the mainjets and drop the needles, while at the same time installing low-restriction air filter(s). This 3-way mod will lean out the "dirty" range and reduce the in-town torque a little, but the personality shifts from Mr. Walker to Mr. Wheeler (remember him?) when you hit 6500 RPM. This is one of the things Honda did with the first "F" 750s, while improving the pipe and compression ratio. They also laid back the cam about 5 degrees, which enriches the top end, too. That's why the "F" feels like a rocket at top RPM, but the "K" tends to out-pull them with heavier loads. The "F" usually does a superior job of cleaning the plugs, as a result. And, some say, it's more fun to ride that way (right, RXman?).  :D

Offline pangloss

  • Enthusiast
  • **
  • Posts: 137
  • CB500 K2 1975 NZ model
Re: Ignition Analysis: Honda's coils
« Reply #54 on: March 30, 2008, 02:39:27 pm »
Hi there,
            While on the subject of ignition, I have just put my old  Cb500-4 back onto the road..It has a Yoshi Road and track cam which requires full ignition advance of 41 ~ 45 degrees

The standard points advance mechanism doesn't really work well for tractability and "manners" at low revs because of its lesser advance range.......Question.....Has anyone tried to fit a fully digital ignition control system that can be "mapped" across full advance curve range...??? Any other alternatives..??

 

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 10,319
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: Ignition Analysis: Honda's coils
« Reply #55 on: March 30, 2008, 04:09:54 pm »
Hi there,
            While on the subject of ignition, I have just put my old  Cb500-4 back onto the road..It has a Yoshi Road and track cam which requires full ignition advance of 41 ~ 45 degrees

The standard points advance mechanism doesn't really work well for tractability and "manners" at low revs because of its lesser advance range.......Question.....Has anyone tried to fit a fully digital ignition control system that can be "mapped" across full advance curve range...??? Any other alternatives..??

 

You can modify the stock advancers by spreading the stops out at the sides where the weights hit them. Alternately, you can grind off a little at a time of those stops until you get what you need. Or, you can go whole-hog and cut them off, then weld on new ones with screws in them that let you adjust for the maximum stop angle. (I've seen all 3 methods.)
The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline pangloss

  • Enthusiast
  • **
  • Posts: 137
  • CB500 K2 1975 NZ model
Re: Ignition Analysis: Honda's coils
« Reply #56 on: April 01, 2008, 12:18:53 pm »
Thanks for the reply...Yes, sound like the best way for now..I'll get hold of an old advance unit and start experimenting....There doesn't appear to be much info on "ignition timing versus engine state of tune" about..  I guess it's all trial and error, either on the road or at a Dyno facility.....

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 10,319
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: Ignition Analysis: Honda's coils
« Reply #57 on: April 01, 2008, 06:29:11 pm »
Thanks for the reply...Yes, sound like the best way for now..I'll get hold of an old advance unit and start experimenting....There doesn't appear to be much info on "ignition timing versus engine state of tune" about..  I guess it's all trial and error, either on the road or at a Dyno facility.....

Generally speaking, it's mostly about the speed-of-burn of the fuel you use. Premium burns slowly, so a little more advance can be used, letting the gases push longer after the TDC is reached, and with higher pressures. Regular burns quickly, so less advance is needed, and the "push" ends sooner, with the combustion pressures being slightly lower as a result. The premium is then easier to tune at high RPM, the regulars at midrange. Most folks ride at midrange, so it's where most manufacturers build their tunes.
The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline CB750R

  • Hot Shot
  • ***
  • Posts: 405
  • 77 CB750F
Re: Ignition Analysis: Honda's coils
« Reply #58 on: May 18, 2008, 07:13:53 pm »
Ok, I have some questions not fully answered on this link, or on the site that I can find, I have already purchased a dyna S, I have stock coils right now, what is the optimal setup? Stock coils? 3ohm coils, with resistor, 5ohm dyna coils? I have two sets of stock coils, one is kinda shocking me when when I grab the #4 lead while bike is running so going to swap something. Bike however runs pretty well as is, but always looking for improvements!

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 10,319
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: Ignition Analysis: Honda's coils
« Reply #59 on: May 18, 2008, 08:46:33 pm »
Ok, I have some questions not fully answered on this link, or on the site that I can find, I have already purchased a dyna S, I have stock coils right now, what is the optimal setup? Stock coils? 3ohm coils, with resistor, 5ohm dyna coils? I have two sets of stock coils, one is kinda shocking me when when I grab the #4 lead while bike is running so going to swap something. Bike however runs pretty well as is, but always looking for improvements!

You'll certainly want to change out that shocking coil before it chews on your leg in the rain, like mine did some years ago. Man, that hurt!  :o

If you're running a halogen headlight (and any other electrical "extras"), you'll want to gravitate toward those 5-ohm coils with the Dyna "S" unit. This will help keep the wiring (now aged) from heating, and will help keep the battery healthier. Overall, the bike will run better. Dyna made those 5-ohm coils for just this reason, mostly triggered by the more marginal charging systems, such as found on the 500/550 and other similar bikes. Since the Dyna "S" causes an increase in current consumption for the whole ignition, switching to higher-than-Honda coil resistances will help offset that current back down to a healthier value.
The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline CB750R

  • Hot Shot
  • ***
  • Posts: 405
  • 77 CB750F
Re: Ignition Analysis: Honda's coils
« Reply #60 on: May 19, 2008, 12:08:05 am »
Thank you sir for your informed reply! Had I paid more attention I probably would have got your system for retaining the stock points, and not needed to upgrade the coils to suit the dyna!  So the Dyna 5 ohms will recharge faster than the old hondas, curing what you described as "the wall" even though they are only 5 ohm not the "hot" 3 ohms everyone runs?  I have a halogen bulb, but running LED tail light, and all my "dash" lights are led's drilled and mounted into my headlight bucket! 

Now as a man who definatly know's his stuff do you happen to know where I can source out 40 or larger ones? I have 35's on my carby's and still getting lean coughing...

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 10,319
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: Ignition Analysis: Honda's coils
« Reply #61 on: May 19, 2008, 06:43:03 pm »
Thank you sir for your informed reply! Had I paid more attention I probably would have got your system for retaining the stock points, and not needed to upgrade the coils to suit the dyna!  So the Dyna 5 ohms will recharge faster than the old hondas, curing what you described as "the wall" even though they are only 5 ohm not the "hot" 3 ohms everyone runs?  I have a halogen bulb, but running LED tail light, and all my "dash" lights are led's drilled and mounted into my headlight bucket! 

Now as a man who definatly know's his stuff do you happen to know where I can source out 40 or larger ones? I have 35's on my carby's and still getting lean coughing...

I think Honda still sells them. It takes a long time to get them, but they seem to be available, from Japan, on special order. I got some 38 size a couple of years ago, took all summer, but they got here in time to have me find the trouble elsewhere. In my case, it was a stubborn, hard-to-seal vacuum leak on cylinders 2-3, which just happened to show up after I did my "750 Hemi" conversion. I change to a different kind of band clamp on those hoses, and that finally fixed it. The stock 35 jet-and-airscrew should reach the range of a 50 idle jet, when the screw is turned out 3/4 extra turn.
The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline CB750R

  • Hot Shot
  • ***
  • Posts: 405
  • 77 CB750F
Re: Ignition Analysis: Honda's coils
« Reply #62 on: May 19, 2008, 08:10:04 pm »
which band clamps did you change? perhaps I too am barking up the wrong tree!

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 10,319
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: Ignition Analysis: Honda's coils
« Reply #63 on: May 20, 2008, 06:16:42 pm »
which band clamps did you change? perhaps I too am barking up the wrong tree!

For my first test, I went and got some genuine Checker Auto 2.5" bands (wide ones) and used them to play with. When it solved the problem, I went and found some proper narrower ones at a hardware store, ones that fit into the little grooves. After a while, I found they leaked, too. At the end of last season, I had added a thin band of steel where the original clamps used to be, then added the wide ones over the top. But, I got the "perfect round" type of clamps the second time, which have an extended wrap of flat band to go under the screw clamp, to make sure the uneven part of the clamp didn't introduce a new leak. It will be interesting to see if it stayed non-leaking after sitting all winter!
The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Phxmark123

  • Guest
Re: Ignition Analysis: Honda's coils
« Reply #64 on: July 07, 2008, 04:36:37 am »
Hondaman: I read the entire thread and where I was keeping up at first my head was spinning at the end with all the years and options. I would like to know your opinion on my current situation and what would be the most cost effective right now and then a price for a Hondaman ignition conversion if so need later. I have a '78 CB750K slightly modified. I just bought it and don't have the jet size of the mains. The PO forgot the jet size but I don't believe it was too massive. The engine had been cleaned up, honed and new rings and it has 2 into 1 pipes with what I believe is the Dyna S ignition module (click on my link in signature to see picture) and stock coils. I was thinking upgrading the coil for the best cost effective measures right now. Your opinion?

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 10,319
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: Ignition Analysis: Honda's coils
« Reply #65 on: July 07, 2008, 08:48:03 pm »
Hondaman: I read the entire thread and where I was keeping up at first my head was spinning at the end with all the years and options. I would like to know your opinion on my current situation and what would be the most cost effective right now and then a price for a Hondaman ignition conversion if so need later. I have a '78 CB750K slightly modified. I just bought it and don't have the jet size of the mains. The PO forgot the jet size but I don't believe it was too massive. The engine had been cleaned up, honed and new rings and it has 2 into 1 pipes with what I believe is the Dyna S ignition module (click on my link in signature to see picture) and stock coils. I was thinking upgrading the coil for the best cost effective measures right now. Your opinion?

If you upgrade to Dyna's 3-ohm coils, get some inline resistors for them, too (1 ohm is about right). If Dyna doesn't have them, I sell some that will fit nicely. If you use their 5-ohm coils, no resistors are needed. Locally, I have seen 2 Dyna S failures this year, both with recently-fitted 3-ohm coils, where they had been using stock coils before. While Dyna seems to think this combination is OK, it raises the currents so much that the Dyna S gets hot and the 750 alternator is heavily loaded.
The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline fishman_Phil

  • Hot Shot
  • ***
  • Posts: 291
Re: Ignition Analysis: Honda's coils
« Reply #66 on: July 07, 2008, 11:15:28 pm »
Hi all ... out of curiosity, are the coils of the 350F, 400F, 500F, 550F, 750F (any others?) interchangeable from one model to another. I would imagine the 350F and 400F are likely to be the same? Answer may help with obtaining parts or spares.
Cheers ... Phil in NZ
1972 Honda CB350F (2); 1975 CB400F; 1983 CBX400F (1); 1962 Suzuki MA50 (1); Suzuki M15 (3); Suzuki M15Mk2 (2); Suzuki M31 (2); 1936 James H12 (2); 1948 Triumph Speed Twin 500; 1989 Suzuki GSXR250F; Yamaha Chappy (2); alot of work yet to be done.

Offline TwoTired

  • Really Old Timer ...
  • *******
  • Posts: 21,084
Re: Ignition Analysis: Honda's coils
« Reply #67 on: July 08, 2008, 01:12:23 am »
Honda has different part numbers for the coils of each bike.  Part of that reason is because the lead lengths are different.  But, the shop manual defines the turns count to be different, too.
EG., The 500 has 420 turns primary and 13,000 turns secondary (30:1).
The 750 has 380 turns primary and 15,000 turns secondary (39.5:1).

750 coils should be capable of higher spark voltage than the 500.

The lower turns count off the 750's coil should translate to a smidge more current draw, which the 750 charging system can take without much issue.
The weaker charging system of the 350, 400, 500, and 550, can benefit from any help in the bike's electrical loading it can get.

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Phxmark123

  • Guest
Re: Ignition Analysis: Honda's coils
« Reply #68 on: July 08, 2008, 06:03:34 am »
Hondaman:

If you upgrade to Dyna's 3-ohm coils, get some inline resistors for them, too (1 ohm is about right). If Dyna doesn't have them, I sell some that will fit nicely. If you use their 5-ohm coils, no resistors are needed. Locally, I have seen 2 Dyna S failures this year, both with recently-fitted 3-ohm coils, where they had been using stock coils before. While Dyna seems to think this combination is OK, it raises the currents so much that the Dyna S gets hot and the 750 alternator is heavily loaded.
With the 5ohm coils do they get as hot and is that setup more reliable?

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 10,319
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: Ignition Analysis: Honda's coils
« Reply #69 on: July 08, 2008, 09:05:57 pm »
Hondaman:

If you upgrade to Dyna's 3-ohm coils, get some inline resistors for them, too (1 ohm is about right). If Dyna doesn't have them, I sell some that will fit nicely. If you use their 5-ohm coils, no resistors are needed. Locally, I have seen 2 Dyna S failures this year, both with recently-fitted 3-ohm coils, where they had been using stock coils before. While Dyna seems to think this combination is OK, it raises the currents so much that the Dyna S gets hot and the 750 alternator is heavily loaded.
With the 5ohm coils do they get as hot and is that setup more reliable?

The 5-ohm should run cooler than stock coils, and the 3-ohm coils. Reliability on the 5 ohm: I can't answer, simply don't have enough experience with them. Maybe some other SOHC4-ers do?
The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Phxmark123

  • Guest
Re: Ignition Analysis: Honda's coils
« Reply #70 on: July 09, 2008, 08:04:51 am »
Thanks for the info, You have seen 3 ohm coils setup being bad. How about 5 ohm setups? I think already from the info 5 ohm setup is what I will work for.

Offline TomC

  • Hot Shot
  • ***
  • Posts: 325
Re: Ignition Analysis: Honda's coils
« Reply #71 on: July 09, 2008, 05:57:34 pm »
Hi TwoTired
     I wondered if there was a way to tell which coil was which. I compared the coils on my 400F1, 550, & 750F1. The marking on the coils is, 400F1 FL703-12V57 F, 550 ( not sure which 550 ) FL703-12V 68L & FL703-12V 67L, 750F1 FL703-12V G. Tomorrow I will check the resistance of these coils.
          TomC in Ohio
quote author=TwoTired link=topic=29545.msg385025#msg385025 date=1215504743]
Honda has different part numbers for the coils of each bike.  Part of that reason is because the lead lengths are different.  But, the shop manual defines the turns count to be different, too.
EG., The 500 has 420 turns primary and 13,000 turns secondary (30:1).
The 750 has 380 turns primary and 15,000 turns secondary (39.5:1).

750 coils should be capable of higher spark voltage than the 500.

The lower turns count off the 750's coil should translate to a smidge more current draw, which the 750 charging system can take without much issue.
The weaker charging system of the 350, 400, 500, and 550, can benefit from any help in the bike's electrical loading it can get.

Cheers,
[/quote]
TomC in Ohio
76 CB750 F1 Daily Rider
76 CB550 stalled project
76 CB400F Injured Reserve

Offline Pinhead

  • Master
  • *****
  • Posts: 1,820
  • 1979 CB652-ST
Re: Ignition Analysis: Honda's coils
« Reply #72 on: July 19, 2008, 12:30:07 pm »
I would also assume that bikes with low resistance coils would respond well to a relayed power circuit; the reduced power draw through the switches would make the entire electrical system more efficient.

I installed a solid-state regulator/rectifier (link in my sig) and installed a relay on the power to the coils. Those two mods greatly decreased the "cold bloodedness" of my CB650 and smoothed the engine out. I would assume the bike's lean-running nature makes ignition performance more noticeable, but improved ignition definitely can't hurt!

Having said that, the CB650's have a transistorized ignition from the factory. Do you have any experience with these units, and if so, how do they stack up to the HM Ignition?
Doug

Click --> Cheap Regulator/Rectifier for any of Honda's 3-phase charging systems (all SOHC4's).

GM HEI Ignition Conversion

Quote from: TwoTired
By the way, I'm going for the tinfoil pants...so they can't read my private thoughts.
:D

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 10,319
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: Ignition Analysis: Honda's coils
« Reply #73 on: July 20, 2008, 09:01:02 am »
I would also assume that bikes with low resistance coils would respond well to a relayed power circuit; the reduced power draw through the switches would make the entire electrical system more efficient.

I installed a solid-state regulator/rectifier (link in my sig) and installed a relay on the power to the coils. Those two mods greatly decreased the "cold bloodedness" of my CB650 and smoothed the engine out. I would assume the bike's lean-running nature makes ignition performance more noticeable, but improved ignition definitely can't hurt!

Having said that, the CB650's have a transistorized ignition from the factory. Do you have any experience with these units, and if so, how do they stack up to the HM Ignition?

All of the things you mention about improving current to the coils is true, provided the alternator can make the extra current to begin with...Japanese designers are notorious, even today, for little tricks like using downsized wire to increase the resistance voltage drops in the whole system so that the alternator does not have to be quite as large. Sometimes, though, they do this to the harm of the product: many of their cars have suffered in winter conditions as a result. The Toyotas before about 1995 are another example of this situation, and these bikes are no exception.

One thing to keep in mind when modifying Japanese electronics of any kind: they will design to use every last bit of power a [solid-state] part can muster, to save $0.0001 on the final product, then build millions of the [solid-state] parts and the product that uses it, to recover the engineering costs. That's just their mindset, always has been. So, if you go and increase power to such a unit, or used by such a unit ("I'm going to use 15 volt electrics", "I'm going to substitute 3-ohm coils for stock ones", etc.), you can quickly overload them and burn them out. I wish I had $5 for every time I've fixed a system damaged this way: I would not have to work today, anymore.  :D

The Honda electronic ignitions have been much like their stock ignitions, in that they work pretty well when everything is 100% correct. But, dropping 10% of performance (i.e., battery voltage, bad contacts from age, bad/wrong plug caps) is enough to make the systems run poorly. They still run, just poorly. To "fix" them, you have to usually clean all connections and replace a bunch of parts, like plug caps, coils, wires, or plugs (or points and condensors). The CB650, CX500, Goldwing, and more, all fall into this category. A bad example: sub in a set of Dyna 2-ohm high-output coils on a Goldwing and take it to a dragstrip: you'll be lucky to run all night with it before it starts smoking the inline resistors for those coils. The wattage of the resistors is set to match only the stock coils of 2.5 to 3.0 ohms, and that last little bit of extra current cooks them. In short, to upgrade these bikes' electricals, you must always look further than just replacing one item: look at the whole system and make decisions based on the interaction of everything, or problems will crop up.

A classic example at SOHC4: using 3-ohm coils on a CB500/550. After 1 week of normal daily in-town riding, the battery voltage will drop to 12 volts or less. Throw in a halogen headlight and a #1157 taillite bulb (instead of the stock #1034), and it will be down to 11.5 volts and a very hot rectifier and alternator stator. The electric start begins to not turn the bike over unless the battery is externally charged (I've seen jumper posts added through sidecovers for nightly charging), the battery will fail over winter storage, and the rectifier will die after it heats up the connectors. The fuse will start blowing on irregular intervals. The problem: almost 3 amps of load have been added to the system, which is 2 more than the alternator can even generate at 13.6 volts. The system will slowly burn itself down while the owner becomes very unhappy, then sells or junks it, and tries it again on a different bike.

In all actuality, I'm seriously considering going into business, looking for these bikes that are in this situation, then rebuilding them correctly and educating the new owners. The first 3 of these are the Hondaman Special 750s, #1, #2, and #3. All 3 of the "source" bikes went through exactly this thing: the wiring harnesses were cooked. Next will be 500/550 bikes.  ;)
The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline TomC

  • Hot Shot
  • ***
  • Posts: 325
Re: Ignition Analysis: Honda's coils
« Reply #74 on: July 25, 2008, 03:52:26 pm »
Hi TwoTired
     I wondered if there was a way to tell which coil was which. I compared the coils on my 400F1, 550, & 750F1. The marking on the coils is, 400F1 FL703-12V57 F, 550 ( not sure which 550 ) FL703-12V 68L & FL703-12V 67L, 750F1 FL703-12V G. Tomorrow I will check the resistance of these coils.
          TomC in Ohio
     Which I did but forgot which thread I was on. All of the above coils measured 4.5 +/- 0.1 ohms. The 750 and 500 coils may have been different when the manuals were written. But by 1976 all the SOHC4 seem to be using the same coil, except for wire length.
            TomC in Ohio
TomC in Ohio
76 CB750 F1 Daily Rider
76 CB550 stalled project
76 CB400F Injured Reserve