no pulse to ony one coil.

[thebigjerm]

1981 cb750
I checked the oncoming pulse to the coils. One is fine the other is not getting anything. Suggestions? Half of pulse generator gone bad?

Thanks in advance.

 

[amc49]

Uh, the only pulse there is going out not in. It goes out both wires. There is nothing to 'get' as they are not powered, rather they generate a power pulse themselves.

If the air gap is too big you can get nothing there. They do occasionally go bad as well.

 

[thebigjerm]

Thanks for the response.
I am only getting pulse signal to one coil. Can generator pulls for one coil and not the other or is it possibly the cdi box?

 

[thebigjerm]

Supposed to say pulse not pulls

 

[amc49]

What are you calling 'coils'? Ignition coils up under tank or the magnetic impulse coils (pulsers) under the left crankcase cover?

You clearly do not understand how the system works. The bikes do NOT have CDI, it is simply a transistorized standard Kettering ignition system.

 

[thebigjerm]

What are you calling 'coils'? Ignition coils up under tank or the magnetic impulse coils (pulsers) under the left crankcase cover?

You clearly do not understand how the system works. The bikes do NOT have CDI, it is simply a transistorized standard Kettering ignition system.

The bike does have two ignition coils they are under the tank/handle bars. one for cylinder 1&4 and one for 2&3. It also has one cdi box feeding each coil they are under the seat above the battery box. It has a pulse generator connected to the crank. That sends signal each cdi box which then sends signal to each coil and then to the plugs.

You are clearly an asshole and I'd rather not hear from you ever again unless you are actually gonna be helpful. CB750 guru my ass. Dick!

 

[thebigjerm]

Description
New Honda OEM Style CDI Box: small OKI style ignition control unit. Some bikes require 2 parts, so please order appropriately.

 

[thebigjerm]

this diagram call them spark unit. some places ive seen call them an ignitor. its all the same thing.

 

[dirtdigger]

Ive known them as ignitors, but same thing, they are a very common failure part on these bikes. I would guess you have a bad one but I would think you could swap them and see if the problem follows the ignitor or if it stays. If it follows then you know its a bad ignitor. If it stays you have other issues, either with wiring or the pulse generators.

 

[Chris in Dorset England]

The bike does have two ignition coils they are under the tank/handle bars. one for cylinder 1&4 and one for 2&3. It also has one cdi box feeding each coil they are under the seat above the battery box. It has a pulse generator connected to the crank. That sends signal each cdi box which then sends signal to each coil and then to the plugs.

You are clearly an asshole and I'd rather not hear from you ever again unless you are actually gonna be helpful. CB750 guru my ass. Dick!

What a very rude person you are.

 

[amc49]

I can be too and apologize.

Still, the boxes are NOT CDI, anybody calling them that is incorrect, and it automatically flaws all testing procedures like here. CDI does not power coils up at all times like these do and a simple Kettering system. Meaning thinking the coils get a 'pulse' is incorrect in its' entirety to answer the first post. The ignitors get the pulse from the pulsers (simple magnetic impulse self powered proximity sensors) not the coils. The coils themselves get fed 12 volt all the time (OP can search for a 'pulse' there until the end of the earth and not find it) and them switching OFF is what makes the spark when the ignitors open the ground up from the coils that they control. CDI coils DO get a single short pulse that is a high voltage hit of around 400 volts or so and you will never get that ever on one of these DOHC, the coils again being 12 volt only. These Honda ignitor boxes are transistor switches only like most cars use, they do not use a cap to charge up to power and discharge like say a Kawasaki true CDI which I worked on plenty of times. Or Honda say on the dirt bikes.

Get that...............these, coils normally ON most of the time, CDI coils normally OFF. That automatically marks the type of system being used there.

People who make the ignitors call them wrong too, nothing surprising at that as many manuals call them erroneously the same as well. Bike people always assume that electronic ignition means it must automatically be CDI and simply not always true.

OP can think whatever he wants, nobody says there is a law that has to be right.

 

[amc49]

http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&t=5

Go there, sign up for free, and the section of technical documents for CB750K, section 17 there, 17-3 pg. 231. The schematic of the inner guts of an ignitor clearly show a transistor (#3) as the switch for the coil ground.

 

[thebigjerm]

Thank you to everyone (especially amc) i am learning on the fly. I will try to switch out the 2 and see if spark follows (never dawned on me to do that...Doooh) lol. This will be a fun project. I hope.

 

[thebigjerm]

Got set of used ignitors. Bike now runs. Time to start the tear down. I already removed a bunch of stuff. Gonna post in classifieds, but don't have a clue if people are interested in take offs or not. Gonna start a rebuild thread as well. Thanks again!

 

[Wilson]

The bike does have two ignition coils they are under the tank/handle bars. one for cylinder 1&4 and one for 2&3. It also has one cdi box feeding each coil they are under the seat above the battery box. It has a pulse generator connected to the crank. That sends signal each cdi box which then sends signal to each coil and then to the plugs.

You are clearly an asshole and I'd rather not hear from you ever again unless you are actually gonna be helpful. CB750 guru my ass. Dick!

Great advice.

 

[Loose Chain]

Great advice.

Not really

 

[mrtwowheel]

Thank you to everyone (especially amc) i am learning on the fly. I will try to switch out the 2 and see if spark follows (never dawned on me to do that...Doooh) lol. This will be a fun project. I hope.

I take it that this is an apology to someone that tried to help you in the way that he saw helpful and you responded by calling him an asshole and a dick? Pretty lame apology. If this forum is ever going to wake up and grow, this shit can't happen.

 

[dirtdigger]

This post was 6 years old before it was resurrected with no real reason. I'll close the thread if nothing useful is going to be contributed.

 

[kzs8nt]

1981 cb750 custom
Squabbles aside, I am chasing electrical gremlins on my classic scoot and find this and other such threads informative and helpful. Bought in July of this year, and two ignition control modules, new battery, new oem style coils, ignition relay, refurbished carbs and a few other bits later, I have finally arrived at the point where the TDI " pulse generators" appear to be faulty. Timing is dead nuts. Swapped ignition control module plug ins and the problem jumped coils according to the telltale strobe light. Keep on keeping on gents. Bike ran great prior, happened suddenly, have not checked compression or valve clearance yet. Winter is near. Just need her to.get me through till hibernation. God bless.

 

[lostincb750f]

Good day/ evening or happy new year.
I have been casing a similar issue. This one has been haunting me for awhile now. Used to loose 1&4, or 2&3 or just any one of them. Sent the bike in they did, cams, compression test, carbs, coils, plug leads amd caps, plugs. Issue still there and I was told to ride as it doesn't like standing. I would live to ride tho at that stage I would ride 10min then it would loose a piston or 2.
I got 2 new "cdi" units from japan and replaced plugs and she ran sweet, took her on a couple of 30mn rides no issues. Then got the team together for a ride and about an hour in lost 1&4. I have since replaced the wiring loom, stata, regulator rectifier, and still nothing on 1&4. I swapped wires and plugs and the colis both work when wired to work on 2&3. Could it be the pulse generator? Can only one go nuts?