1982 cb900f resurrection NO SPARK???

[Anonible]

Let me begin by saying that I am new to the forum but have read many a post since 2010 after purchasing my first bike, a running 1979 cb750k, which has since gone through some major changes.

Will eventually post some of the 79' in the appropriate sections at a later date.

Back to the problem at hand, I have a 82' cb900f that has sat for approximately at least 10 years in the yard of it's previous owner.

Since the purchase I have fixed the existing wiring using some spare connectors, checked wire for damage, re-wrapped the entire harness, replaced spark plugs, and got the bike to spark initially with old lead acid battery I had laying around.

However I could not get bike to fire.

Eventually decided the battery was no longer any good and swapped oem battery for a new sealed one. Re-tried firing er up and was unsuccessful. Re-checked for spark, and found that I had no spark at any plug.

Checked the usual common-sense contenders; igntion on? Check. Kill switch set to run? Check. Good Frame Ground? Check. Fuses good? Check.

Then preceded to check for a problem at starter switch and found nothing. Pulled out the multimeter and started trying to trace 12v and found that it was reaching both coils and read 12v at the black and white wire.

Checked points and timing, and bench set them to oem specs. Swapped out spark units with ones known to be good, Same with coils and wires. Still no change.

Neutral light is on and bike is truly in neutral. Starter turns motor over just fine and am getting fuel into cylinders.

Will do some more manual reading. Been going through Clymers (a dohc cb750 one) and Haynes (dohc cb750-cb900) alike trying to diagnose what the hell is going on.

Admittedly I am not versed in the use of a multi-meter beyond checking for voltage.

Spending tonight going through the cb750 shop manual that I may or may not have found here on this forum (I cannot remember), in hopes that between the hundreds of pages, there are instructions to lead me to what is preventing me from glorious success.

Sorry for the long initial post, but I hope that it makes this go much quicker without having to play 100 questions.

Thanks

[Rodgil]

Download the factory service manual (FSM) from this website. It is better than the other ones.  You still have no spark? Refer to the ignition section and test the pulse generator with your multimeter. It is easy to do at the connector just below the starter solenoid. And when you do get spark, make sure you have fresh fuel, even drain the old fuel from the carbys by opening the screws at the bottom of the float bowls.

[Anonible]

I do have the entire FSM printed out and in a large binder. Replaced the pulse generator with a spare from another bike, also swapped coils and plug wires/boots from a running dohc cb750. Still no spark... Going to rip out the harness and re-plug everything yet again in hopes that theres something I've overlooked...

[TOOLS1]

Did the ignition switch go bad? They are just a crapy piece of plastic with contacts in it mounted under the key switch. I have replaced a few of them over the years.
TOOLS

[Anonible]

Starter turns over and everything. But I will replace it tomorrow and see if that is indeed the problem. I have a 82' cb750c parts bike I have been pulling parts from.

Thanks for the suggestions.

[shinyribs]

Since you are seeing voltage at the coils your ignition switch would seem to be ok to me. Your problem may be in the plug wires themselves.

The boots just screw on. I'd unscrew them and see what things look like. There is a tip in there that just looks like a wood screw. You may need to trim a bit of plug wire off to reach good,healthy wire. It's possible you are making spark and It just cant reach the plugs.

You can set your meter to ohms and pierce one lead into the plug wire thru the insulation and check for continuity between that point and the tip of the boot that would contact the plug. That should tell you if your plug wire is able to transfer the energy from the coil to your plug.

[Anonible]

Thanks for your response shinyribs, however as I have stated previously, the coils wire and plugs have been borrowed from my running cb750 and are in good working condition, so I do not believe that should be the problem. Also put the cb900 coils plugs and wires in my cb750 and she fired right up and ran fine. Have noticed the ignition keys sometimes needs a little wiggle when in on position to get neutral light to come on. So I will do a ignition switch swap here when I get back from mother's day shopping.

Will post update when I've got that done.

Thanks again.

[shinyribs]

Anonible wrote

..... however as I have stated previously, the coils wire and plugs have been borrowed from my running cb750 and are in good working condition...

This is why I shouldn't be posting at 3 am.

[Anonible]

No big deal.

This is where I am at now; replaced ignition switch and start/stop switch.

Still no spark...

Going to remove harness and re-plug everything outside of frame.

Battery is fully charged...

[TOOLS1]

Are the spark plugs you are using for testing good? Are you grounding them good to the engine when testing?
TOOLS

[Anonible]

Re-plugging all connections and grounds did nothing. Tried yet another start/stop switch to no avail.

Spark plugs are all brand new and gapped correctly. Grounding plugs by their threads to head or head bolts. Neither is producing anything different. Even tried on different plug wires.

I am at a total loss as to what is going wrong.

[TOOLS1]

Check the ignition trigger on the end of the crank. It might not be working.
TOOLS

[Anonible]

Are you referring to the pulse generator that is located left engine side whilst on the bike? I have already swapped it and still nothing.

[Anonible]

Okay so I've figgered out why I was not getting spark after all...

When all else fails...

It's the handlebars...

Were not grounded well enough, even though risers had the piss tightened out of them.

Now I and hearing a carb sucking noise and see what looks like gas mixture causing moisture around intake boots.

Going to swap out some clamps tomorrow and will hopefully get er fired.

heard her try to fire once or twice but air leak just too much, even with some fuel down cylinders 1 and 4.

Thanks again everyone who posted help.

[alero29]

Resurrecting this thread!  I am in the same boat as Anonible was and am looking for some help from anyone willing!

Here is a bit about my bike first.

1982 CB900F SS I have done a front end fork/triple/brake swap from a 2005 GSXR1000 and a rear swing-arm swap with a 2012 Hypermotard 1100 SP.

I have maintained the stock wiring harness, fuse panel, hand controls (i.e. kill switch, start, blinkers, etc.).  The only real changes electrically at this point is I have a new headlight, no tail light (currently in project mode), new Lithium Iron battery, New 'Rick's' Lithium Iron Regulator/Rectifier.

About 3-4 years ago I rode this bike into the garage (running).  I tore it down and have been working on the rebuild (very, very slowly) ever since.  Late last summer I finally got it put together enough to try and start it.  It started cranking and turning the engine over without trouble right away.  It never started.  I did all of the usual checks. Air (check, Gas (check), Spark (negative)......

Digging deeper into the no spark issue I found I didn't have any spark at any cylinders..... I've checked  most of the obvious stuff and what I believe to be unrelated stuff. Voltage at coils (check), clutch switch, bike in neutral, pulse generator, stator, regulator/rectifier and I cant come up with anything!

I found this post and wanted to see if any one could explain how the handlebar controls ground.  I replaced the stock bars with powder coated clip ons and now I am suspicious I have a ground issue. (I even sandwiched ground wires between the left and right controls to make sure they are grounding).

Sorry for the long post.

Any thoughts???

[TOOLS1]

Honda runs ground wires to the switches, so the handlebars do not need to be grounded. The ground wires are "green". Since you have voltage everywhere else on the bike, your main fuse is not blown. You have voltage at the coils. The voltage comes from the ignition switch to the coils, and then to the ignition/CDI. You also need a separate voltage supply to the CDI unit. Do you have it there? Have you checked the coils?
You can download the factory service manual from the manual section here. It has a wiring diagram.
TOOLS

[alero29]

TOOLS , thanks for the quick response!  I have verified main fuse looks good.  I do have voltage at the coils.  Quick question though is black/white stripe wires on + side or - side?  The schematic isn't very clear about this...

I have checked the coils and they seem to check out.  Plus it seems unusual to me that I would have both coils fail or both spark units fail. I did verify that I have a 12 volt supply (closer to 10.8V with low battery and headlight on) at the spark units blue wire/yellow tube and on the other connectors yellow wire.

Some other items to note.  When I switch the key on the headlight doesn't stay on unless I turn it back towards off slightly.  It appears that mechanism is worn or perhaps corroded.  

Also, I did find I get a single spark from the spark plug(s) as I am releasing the starter button.  That is the only time there is spark.  There are instances where I don't get that single spark but it does seem to be pretty consistent.

[TOOLS1]

The black/white wire should go from the ignition switch to the positive side of the coil. There is also a feature that turns off the headlight when the starter button is depressed like on cars. You might have a bad ignition switch. They are just plastic pices that attech to the botton of the key cylinder.
TOOLS

[alero29]

I was kind of thinking the same.  Potentially a weak contact inside the switch that once I hit the start button there is too much load so it fails.  I am thinking I will just try to temporarily bypass the switch to start it and see if I get the same no spark result.

It appears I can just jumper the 'Red' (Batt) to the ' Black' (Ignition) to do this?

[TOOLS1]

Yes.
TOOLS