Topic: Getting frustrated now

[rhos1355]

Hi Folks,
I've been doing a "nut & bolt" restoration on a CB750 K2 I bought 6  years ago. This winter after working away from home for 2 years, I got the motivation back to spend some time in the shed with the bike and see if I can finish it off.
I did a fair bit of wrenching when I was in my late teen/early twenties but was never what I would call "skilled". Just loved machines and engines and finding out how they worked.
Here's my problem, and I would much appreciate any feedback to my questions: after successfull firing her (I call the bike "her") up about 2 weeks ago for the first time, I always seem to struggle starting her again the next day or a couple of days later. A whole myriad of problems crop up, from dirty fuel (clean out the tank and carb wells), sticking float needles (remove, clean out the gunge and replace), dodgy spark lead caps (replace with new ones). On and on it goes.
So far it has new; coils & leads (these are actually bought new 6 years ago), spark plugs and caps, contact points and condensors (also bought new 6 years ago), oh and the wiring loom is new.
The latest hang-up is no spark at the plugs. Nuthin', zilch, zero, nada, dead as a dodo. I've checked the usual suspect of the "kill switch" with a continuity test along the black & white wires, that was ok. I also did a continuity test on both the yellow and blue wires coming from the coils to the contact points, they were ok. but NO sparrk a the contact points. I swopped the new condensors for the old ones I replaced 6 years ago, still no spark. In desperation I ordered 2 new ones from David Silver and should arrive Tues/Wed.
Am I on the right track or am I barking up the wrong tree? Should I be checking other wires? How do you check that the coils are ok (without resorting to buying new ones)
Finally, considering all the ignition problems I've been having would you folks consider electronic ignition? If so, what make, model, part no. etc?
Once I can get her to start reliably, I intend to synchronise the carbs. I have already set the air intake jets and the carb throttle rods to the settings in the Haynes Manual.

Thanks

[bruzer59]

you can test your coils with a meter on low ohms scale by touching the probes to black/white under the tank at the 3-way connector( coil wires unplugged ) and to blue and yellow wires disconnected from points.... must read very close to 5 ohms for stock coils.( Primary )
Fast test would be to open both points by sliding a piece of card between the point faces , turn on ign. and test for +12v at each point wire ( blue and yellow) btw, coils very rarely go bad/fail,

[splitt]

Is your battery fully charged? (12.5 volts after charging is what I look for) Are you getting voltage to the coils on the black/white wire with the key switch on? You've already checked the kill switch. Test the coils and points like bruzer59 says. Test the condensers with a multimeter. Disconnect the condensers from the points, Put one probe on the spade connector and the other to the body of the condenser. If it reads approximately 0 ohms, the condenser is bad.

Dumb questions here. Are your fuses good? Do you have good ground wires and connections?

Before entering an electronic ignition into this equation, I'd make sure that you have a good running stock ignition first.

[rhos1355]

Is your battery fully charged? (12.5 volts after charging is what I look for) Are you getting voltage to the coils on the black/white wire with the key switch on? You've already checked the kill switch. Test the coils and points like bruzer59 says. Test the condensers with a multimeter. Disconnect the condensers from the points, Put one probe on the spade connector and the other to the body of the condenser. If it reads approximately 0 ohms, the condenser is bad.

Dumb questions here. Are your fuses good? Do you have good ground wires and connections?

Before entering an electronic ignition into this equation, I'd make sure that you have a good running stock ignition first.

Thanks for getting back folks. Now some answers to your questions:
Battery is fully loaded, not only that but I have borrowed a nice 600A tractor battery that I linked to the bike battery for extra oomph.
Fuses are good
earth seems to be ok on the main battery but where does the ignition earth to?

Will check both the coils and the condensors asap.

With me there's no such thing as a dumb question..............the dumber the better, you never know, I have most prolly overlooked the obvious.

Much appreciated guys

[trueblue]

Spark earths through the head, and the 12v primary circuit earths through the points to the case.  The best way to check coils, first have your points open, then check for power at the coil, with the points open you should have 12v either side of the coil, then check the wire at the points you should have 12v there too.  After that manually bridge the wire from the points to earth, when you remove it from earth you should get spark.  BE CAREFUL this wire produces upwards of 200V as you disconnect it from the earth, it hurts.  Then reconnect it to the points, checking the gap when they are most open, then try it.  Condensors won't cause a no spark issue, but will cause running issues.

[wrenchmuch]

Battery earths to the frame at the rear upper engine mount left side. The harness gets its ground from a ring terminal attached to the frame by the seat latch. Both these frame connections should be clean. File or sand the frame where the terminal mounts and re clean every couple of years. This sounds like a wiring issue.

[Magpie]

I had a similar problem with a buddie's bike. You said the wiring loom is new so you have been working on the mess of wires in the headlight. We found by switching some of the black wires in that mess to other black connectors, even though the black wires should all be in one circuit, it did make a difference and the bike fired. It doesn't make much sense but you can use a tester to see which black wire will give power to the coils I think. Worth a try. Cliff.

[mcpuffett]

Hi Rhos it sounds like you have more than one issue to deal with but they are all basic issues  ,

i would make a list of things to check, clean, set etc and go from there,

if your having trouble with dirty fuel start there clean the tank & carbs out then move on to electrical connections, points timing etc,

keep us posted with your progress  , cheers Mick. 

[rhos1355]

Hi Rhos it sounds like you have more than one issue to deal with but they are all basic issues  ,

i would make a list of things to check, clean, set etc and go from there,

if your having trouble with dirty fuel start there clean the tank & carbs out then move on to electrical connections, points timing etc,

keep us posted with your progress  , cheers Mick.

Hi Mick,
Appreciate your post, I got a horrible feeling this one is gonna be the beast from hell. Always was temperamental, even before I started the strip down. I'm gonna do the electrics to see if I can sort out the spark issue first, then sort out the dirty fuel/tank issues. Just would like it to be reliable. Maybe that's why the PO sold it to me. Now there's a thought. I refuse to sell her 'cos I know for sure the new owner will just tweak something somewhere and fire her up pronto. And gloat. Haha

[rhos1355]

Hello guys, here's an update on what I've found by following your very useful suggestions:

checked my coils as described and they show 4.7Ohms for both Blue and Yellow. I reckon that's close enough to what you said (5 Ohms), Bruzer.

Battery is/was just under full charge; between 11 and 12 v

Voltage check on incoming black/white wire: 11+v

Ohm check on condensors: inconclusive as whatever range I set the meter it always shows 1. I have replaced the condensors with new ones anyway so they should be ok.

Fuse: good

Have 11.05v on either side of coils with contact points jammed open with plastic blade.

bridged contacts to base when I detached the connection to base I got a nice whalloping spark.

turned the crank round manually at the contacts with ignition on and I got spark.

I also used a strobe pistol a friend lent me. when I turned the engine and one by one passed each wire (black/white, blue, yellow) thru the induction clamp, the light flashed.

All except the high tension leads to the plugs.

I am getting the impression that the secondary circuit is damaged, but the primary circuit is ok.

Am I barking up the right tree??

[iron_worker]

11v is very low. I believe anything under 12v is considered pretty much 100% dead. Charge it up and try again. You may just have too weak of a battery to fire the coils properly.

IW

[lucky]

Quote:  "All except the high tension leads to the plugs."

Did you clamp the timing light onto the wires leading to the spark plugs? And DID you get flashes of the strobe?

[rhos1355]

Quote:  "All except the high tension leads to the plugs."

Did you clamp the timing light onto the wires leading to the spark plugs? And DID you get flashes of the strobe?

Yes I did, mate, and there was no flash on any of them. I even remembered to check them with the plug in the engine therefore the circuit is earthed. Still no flash.

[lucky]

If you hook up a 600 amp battery to your motorcycle there could be big trouble.

[rhos1355]

If you hook up a 600 amp battery to your motorcycle there could be big trouble.

Sorry Lucky, you're talking to a real dumbass here......could you describe what kind of trouble? Burnt wires? Popping bulbs?


Carrying on with the dumbass theme, are coils supposed to be earthed? If so, where? Through it's holding clamps? Or just through the plugs?

[Rgconner]

Don't worry over what lucky says. He has reading comprehension problems.

Amps a just a measurement of capacity. Means you can leave the lights on longer without it running down.

Well, unless you have the smaller battery in parallel. Then the big battery might burn out the smaller battery if they don't have the same charge levels.

back to the problem. If you have 12.5v ish at the battery, and 11v elsewhere, you have a wiring problem. A conductor is acting as a resistor.

This is with the key off, of course. Turn the key on and pull from the ignition and lights will drop the voltage, but 1.5 is a bit much, especially with that beefy battery attached.

All the power runs through the key switch by default. If it is corroded it will drop the voltage. I put in HondaMan's relay so that the main voltage does not go through the switch. Much less loss due to the key switch.

[wvshooter]

As someone said, 11 volts is way low. You should also know that your battery could be bad even if you get it to read 12.5 volts. It's the batteries output under load that matters. You probably should have one of the auto parts stores check it to be sure what it's condition is.

[rhos1355]

Thanks for your contributions guys, I appreciate it.
But I think we're digressing on the "is the battery fully charged?" question. In the past I have jump started bikes with very low power in the battery by rolling it down a hill. So I don't really subscribe to the "11 volts is too low" theory.
Anyway, in order to tick that one off the list I charged the battery up yesterday and now it holds a healthy 12.7 volts.
But I still don't get any current throught the spark plug lead. There's a spark at the points and both the yellow and blue and black/white wires strobe nicely, but nuthing at the HT lead.
Funny thing is I put the old coils back on and the same thing: spark & strobe on all the wires except HT.
I find it hard to beleive that the secondary circuit in BOTH coils, both new and old sets have failed.
What do you reckon guys, catastrophic coil failure? Or am I missing something?

Once again, much appreciated.

[iron_worker]

Sparking at the points but not at the plug... interesting.

Since you say the yellow/blue and white/black are strobing nicely I assume you are testing with an inductive timing light?

The only thing I could think of is if you were for some reason holding the spark plug boot with spark plug in it and looking for spark but not grounding it out to the block or some such but that doesn't sound like it's the case.

The only thing I can suggest is possibly clean all your connections at your coil. Perhaps the return path on the HT side is badly corroded ... however even this theory has flaws as I think about it since the HT side has so much voltage it should find a path to ground much easier than the LT side.

Can you potentially borrow a set of coils from a buddy?

IW

[iron_worker]

Another question.... when you replaced your plugs and plug caps did you get the correct resistance?

5k ohm plugs and 5k ohm caps or 10k caps and non-resistor plugs?

IW

[Teatimetim]

I would check the connection near the coils.  On my 550 the connectors were just dirty enough to cause no spark 

[rhos1355]

Thanks guys, I shall try out your suggestions as soon as I can.

Cheers

[jstfkndi]

+1 on touching the spark plug to the head. I made the mistake of thinking my coils were bad by not doing this. Only found out by accident when it shocked my fingers from holding it and I layed it on the head to eliminate that! Funny how it worked, but it turned out it was a carb issue for me.

[Round Dice]

Those are all good suggestions but I find it odd that ALL FOUR are not sparking.  To me that suggests something like the motor ground is bad (electrical connection from motor to frame).