1977 cb750k spark problem

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1977 cb750k spark problem

sfaulk320
Hey guys im new to the world of motorcycles and my first project is a 1977 cb750k i have no idea how many miles on it or much about it at all. So to get to my question, im sure the coil for 2-3 is dead and im getting 9.7 volts out of the 1-4 coil the book i have been reading in one diagram it shows a resistor, i then looked at the wiring schematic i dont see one, so do the coils have a built in resistor if not any ideas where it is and what volts it drops down to? Any feed back will help because i wanna use everything i do as a learning experience not just change a bunch of stuff and not figure out what the problem is.1977 cb750 as i bought it
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Re: 1977 cb750k spark problem

TOOLS1
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As long as you have 9 volts going to the points, you should be fine. However you test the coils by testing the resistance between the two plug wires, and the two connector wires. You can download the factory service manual for free from the manuals link at the top of the home page here. It shows detailed instructions on how to test the coils.
I really like your knobby tires.
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1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Re: 1977 cb750k spark problem

Re-run
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In reply to this post by sfaulk320
When you get the manual, just get the 78 f/k as the 77 is about the same other than maybe a bit on wiring.
Also, use the second set of links. Our primary host went down and I am still holding slight hope for a bit that they come back.
The ride IS the adventure. The destination is just to get gas!
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Re: 1977 cb750k spark problem

sfaulk320
In reply to this post by sfaulk320
Thanks guys the manual will do me good. Thanks for the help once i get the bike fired and running what do you think about swapping from points to electronic ignition setup?  The tires came with the bike i havent made up my mind if im gonna run them or not.
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Re: 1977 cb750k spark problem

Re-run
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Well, you will get differing opinions on the electronic ignition so lets address the tires first.

Two issues with the tires, age and grip. A knobby tire will not give as much grip on pavement when compared to street tire, they look cool though.

A bigger issue is the age of the tire. Old tires are hard and offer little traction. Most manufacturers recommend 5 year replacements. I don't know if I fully buy that but over 7 years I would toss regardless of life, especially if you like corners or end up riding in the rain. http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=11

As for ignition, it depends on what you want.  IMHO, electronic is better DEPENDING on the unit.

In my experience and others I have met, an electronic has offered these benefits:
1: faster, easier starting. My cb starts with barely the push of the button. It started quick before, but now it fairly leaps to life, even when cold.
2: quicker warm up times. less time spent on choke.
3: better fuel economy. most see a couple mpg increase in economy., but not all people do.
4: virtually no maintenance. Once it is set, a quick check just to make sure nothing is loose or coming apart is about all it takes. In my case, I checked mine once...about 5 years after I put it on.
5: better spark. This one is big really. See, a typical electronic unit allows for greater dwell time, this allows the coil to saturate more and provide better spark. of course, a coil can only hold so much but it is well known that a cb ignition system isn't overly strong. This is the primary reason why Iridium plugs do so well on these bikes. Iridium plugs make very efficient use of spark energy, even on weak systems.

now, points proponents cite these reason to keep points:
1: reliability. this is one of those areas that can be debated a long time. We have a small site here and so a poll woun't reveal much. On a larger site, a poll had been done. It was years back and so may not be as accurate anymore. It revealed that more people had failures with electronic than with points, BUT points didnt win by that much. In most cases, it was the rubbing block that broke off. This also compared older dyna S units which DID have higher failures. Moving to a dyna 2000 dropped failures greatly, but costs more. Now, people have the dyna S, dyna 2000(or whatever it is now), cycleX makes an optical, and there is a Pamco ignition which has a good record.

2: easy to carry spares, can't deny that, points are small and can be taped to the back of a side cover.

3: easy to set. Well, yes and no. Once you are used to them, they are very easy to set amd can be set with just a business card really, though optimum spark can't be achieved that way. A dwell meter is best but simple feeler gauges do perfectly fine.

4: some people just like to work on their points. Some people view working on their bike as therapeutic. heck, I do to sometimes. points are an easy thing to get lost in and spend time on while letting your mind wander.

At one time, easy of parts was a factor, but not any more. The average auto parts store, or even motorcycle parts store does not carry much for points. Now, if you convert to Corvette points, you have more options as well as more durability and reduced maintenance.

Now, don't get me wrong, points will work perfectly fine and on a stock bike, there is absolutely no reason to switch. Points will get to where ever you want to go and aside from somewhat frequent maintenance, dressing and adjusting, will rarely fail. I ran points for years before switching and they never failed. I just got better performance from a dyna S. IF you do stick with points, change out the plugs to iridium plugs, AFTER you make sure the bike is tuned right. Points and iridiums work very well.

Now, IF you decide to do some engine work, you may want to consider switching. If you do a simple 836 and mild cam, you are probably ok. Your plugs will tell you for sure.
if you do a 836 with high compression, a taller cam and some additional work, an electronic is the way to go.

This was probably clear as mud but the bottom line is either is fine.
The ride IS the adventure. The destination is just to get gas!