Author Topic: Please help..weak spark and only when letting off starter (Read 8547 times)

AndyJ · « **on:** November 26, 2011, 07:32:16 AM »

Hi guys and gals,

New to the forums, made long intro yesterday.
I'm hoping someone can help/shed some light for me. I purchased a 77 CB750K a couple months ago, it was in fair to poor condition cosmetically but ran strong, I rode it 220 miles the day I purchased it.
Since then I have completely disassembled the bike had the frame powdercoated and refinished the engine externally, cleaned the carbs, and basically got it all back together a week ago.
Very long story short; have spark but only when letting of the starter, she fired a few times and has backfired several times. New battery, plugs, and filed all metal grounding surfaces including the frame.
I've searched here for a remedy and have looked at the points they seem ok,but what has me is that it ran perfectly fine before I disassembled the bike and now she won't start at all.
Any suggestions or personal experience would be greatly appreciated.
Also, already checked the kill switch its good, and I have the correct wires going to the correct coils.
Wires and caps all measure 2.7-3.5 ohms, couldn't get a good read from the coils.
Starter solenoid is bad so I'm using a screwdriver across the top of it to crank the bike, would this cause a faulty spark??

Thanks so much,
Andy

Spanner 1 · « **Reply #1 on:** November 26, 2011, 07:43:50 AM »

Is the Red wire ( to the fuse box ) on the wrong terminal of the solenoid ?

tlbranth · « **Reply #2 on:** November 26, 2011, 09:36:02 AM »

It sounds like maybe a weak battery or a bad battery connection. Have you tried jumping it from a car battery?

grcamna2 · « **Reply #3 on:** November 26, 2011, 03:51:52 PM »

Check to make sure that your coil brackets are nicely grounded to the frame along w/ all the other frame to harness ground straps... & +1 on the battery condition.

dave500 · « **Reply #4 on:** November 26, 2011, 04:08:14 PM »

2.7-3.5 ohms sounds wrong,the caps should measure about 5000 ohms.

AndyJ · « **Reply #5 on:** November 26, 2011, 06:14:59 PM »

Ok, I switched the connections on the solenoid and still nothing, then I connected the battery up to my car with some jumper cables let it crank for about 10 seconds and then VROOM she fired up, idle was a bit rough and died out after a few minutes when bowls emptied out (tank was off).
What still has me scratching my head is that it didn't start until the point where I was removing the screwdriver essentially letting off of the starter, and the four or five times after that it was the same way...cranks and cranks and cranks and fires the second I let off the starter. Any other ideas or insight on what the culprit may be? When I purchased the bike one of the things that I remember clearly and even bragged about to my wife and Dad was that the bike always started the instant you tap the starter button, it wouldn't even crank over it would just be running instantly, now that I've disassembled and reassembled everything it's just not the same including the fact that my solenoid is no good just clicking.
Thanks again for all your help and input.

Something else I failed to mention is that these coils are definitely not for this bike neither are the wires and caps, so the way they're mounted/grounded is a bit odd, I'm only using one mounting bracket and have both coils mounted in the same location. No strap or back coil mount, these things were zip tied on when I bought the bike and again it ran good.

Andy

scottly · « **Reply #6 on:** November 26, 2011, 06:28:00 PM »

Quote from: AndyJ on November 26, 2011, 06:14:59 PM

now that I've disassembled and reassembled everything it's just not the same including the fact that my solenoid is no good just clicking.
Thanks again for all your help and input.

So the only way you can crank the motor over is to short across the big solenoid terminals with a screwdriver? Even with the battery being jumped?

scottly · « **Reply #7 on:** November 26, 2011, 06:33:41 PM »

Quote from: AndyJ on November 26, 2011, 06:14:59 PM

Something else I failed to mention is that these coils are definitely not for this bike neither are the wires and caps, so the way they're mounted/grounded is a bit odd, I'm only using one mounting bracket and have both coils mounted in the same location. No strap or back coil mount, these things were zip tied on when I bought the bike and again it ran good.

Andy

The stock wiring harness is grounded under one of the coil mounting bolts. There should be a green wire with an eyelet on it in that area. It MUST have a good connection to the frame.

Tews19 · « **Reply #8 on:** November 26, 2011, 07:15:48 PM »

I am not sure if this is 100 precent true, but I was informed never to jump a bike from a car. Can reak havoc on the electricals on the bike and fry the rectifier... I may be wrong though.

Is the battery a self filling one? One where you have to put in the acid yourself? If so, you usually have to fully charge before trying to use. If you use before fully charge it can damage the battery

grcamna2 · « **Reply #9 on:** November 26, 2011, 07:17:45 PM »

Make sure your coils are solidly mounted & grounded to the frame...it's important for a hot spark.When frames are painted/powder coated the old connections that used to be good grounds are not there anymore.They must have bare metal contact on the frame between all the ground connections because your frame assembly is used as a common ground for all of them & they really do need to have that common connection.
It will be necessary to get the correct coil bracket w/ correct coils & plug caps for your 77' CB750K...Ebay has a few & you can get the complete set...or try this forum "parts for sale".

AndyJ · « **Reply #10 on:** November 27, 2011, 09:26:28 PM »

Thanks for all the comments.
The battery is a new maintenance free gel battery, it had plenty of cranking amps but did wear down pretty quick. The bike started for the first time when I had jumped it from my car and about 4 times shortly after that without the jump while it was warm. Now it won't start again. I did make sure to completely file the Powdercoating of off the frame where the coils mount, I have bare metal and even filed all contact points on the coils and aluminum bracket and also made sure to connect the green ground wire. The only diffence between before and now is that both coils were mounted separately to each bracket and now they are mounted together on only one bracket, would this make a difference?

Wen I had the jumper cables on it still only clicked at the solenoid I'm assuming it's no good, same thing after reversing connections on it.

Thanks again for all the input and help. Since I'm on a budget I didn't want to spend another penny on getting it running so I'm hoping to figure this out as is... Thanks again!
Andy

grcamna2 · « **Reply #11 on:** November 28, 2011, 06:00:20 AM »

It's tough to fix a 35+ year old motorcycle w/ just "pennies";these Vintage Honda's are very tough & durable & they were Originally built to last.

Rigid · « **Reply #12 on:** November 28, 2011, 07:32:44 AM »

You have me thinking on this one. I have experienced the spark at the moment the starter button is released also. Could this be the collapsing field in the coil being initiated by the removal of the power to the coils? If that is the case, I would suspect a grounded condenser, points not having continuity, or something amiss in the wires you reinstalled for the ignition.

crazypj · « **Reply #13 on:** November 28, 2011, 09:29:10 AM »

Re-do all the frame grounds, at least 1 engine mounting plate (you did remove paint before re-fitting electrical connectors?)
Get a new battery, (check voltage when it's cranking, you will probably find it's dropping too low)

Spanner 1 · « **Reply #14 on:** November 28, 2011, 03:15:38 PM »

Rigid +1.... the point wires ( Blue and Yellow ) are shorted, 'prolly attached wrong @ the points; insulator washers misplaced. Result would be the coils 'on' all the time and the instant the keyswitch is turned 'off' the collapse in the coils produces a spark, just like opening the points

AndyJ · « **Reply #15 on:** December 08, 2011, 12:55:10 PM »

Quick update and "thanks" to all the suggestions.
I installed new coils, new points, new NGK caps, new condensers and a new starter solenoid, and already had new spark plugs.
After all that, I had a stronger spark but get this....still only when letting off the starter button. Not to mention that it cranks fairly slow and clicks at the same time but the ole screwdriver method still cranks it over very fast. Either way I'm only getting it to spark or fire when letting off the starter.
I've also figured out that the choke was not closing all the way (had filters off). So after manually closing the butterfly valves and a few fast cranks with the screwdriver it did start up, but it's not easy starting unless that is by the kick starter.
With choke closed all the way she'll start right up on the first kick!

Has anyone ever converted a cable choke to a manual lever type, perhaps by drilling and installing a lever??

Thanks again guys for all your help.
Andy

tlbranth · « **Reply #16 on:** December 08, 2011, 02:01:54 PM »

Andy, have you had your battery load -tested? They'll check it for free at most car-parts places like Napa.

crazypj · « **Reply #17 on:** December 08, 2011, 05:12:09 PM »

Quote from: AndyJ on December 08, 2011, 12:55:10 PM

After all that, I had a stronger spark but get this....still only when letting off the starter button. Not to mention that it cranks fairly slow and clicks at the same time but the ole screwdriver method still cranks it over very fast. Either way I'm only getting it to spark or fire when letting off the starter.
Thanks again guys for all your help.
Andy

Stop messing about and get a new battery.
The underlined part is a common sign when battery can't put out enough amps for starter and ignition.
You could do an amp draw on starter cable (measuring points at 19.1" on 8 gauge cable 'shunt' and measure in millivolts)

tlbranth · « **Reply #18 on:** December 08, 2011, 05:39:29 PM »

Quote from: crazypj on December 08, 2011, 05:12:09 PM

Quote from: AndyJ on December 08, 2011, 12:55:10 PM
After all that, I had a stronger spark but get this....still only when letting off the starter button. Not to mention that it cranks fairly slow and clicks at the same time but the ole screwdriver method still cranks it over very fast. Either way I'm only getting it to spark or fire when letting off the starter.
Thanks again guys for all your help.
Andy

Stop messing about and get a new battery.
The underlined part is a common sign when battery can't put out enough amps for starter and ignition.
You could do an amp draw on starter cable (measuring points at 19.1" on 8 gauge cable 'shunt' and measure in millivolts)

Well Crazy, batteries aren't cheap. But a load test on the thing would indicate its condition. As I suggested earlier though, a simpler thing is to hook up a car battery and see how it does. Done it lots of times. Don't see any reason it'd hurt the bike, unless you hooked it up backwards. 12volts is 12 volts.

AndyJ · « **Reply #19 on:** December 08, 2011, 06:33:09 PM »

Thanks for the input guys, but as stated in my original post I had already purchased a new battery. It's the sealed, maintenance free type.
Why will it crank fast with a screw driver across the solenoid posts but slow and clicks when using the starter button after installing a new solenoid?
After all this I'll probably end up primarily kick starting it since it does start right up that way, plus it's way cooler

onepieceatatime · « **Reply #20 on:** December 08, 2011, 06:37:46 PM »

Similar thread here.
http://forums.sohc4.net/index.php?topic=91494.0;topicseen

crazypj · « **Reply #21 on:** December 08, 2011, 10:04:27 PM »

Faulty solenoid is the only other reason.
Remove cable to starter and connect voltmeter in there
check it;s getting full battery voltage on output side of solenoid.
I had forgotten that the contactors burn away.
The solenoid still operates fine but the stopper inside prevents full contact
It is possible to take them apart and flip the moving copper contactor (may ned to unsolder the very fine control wires)
I've done it a few times for people, gets a few months~years extra use

faux fiddy · « **Reply #22 on:** December 15, 2011, 03:31:53 AM »

Quote from: AndyJ on December 08, 2011, 06:33:09 PM

Why will it crank fast with a screw driver across the solenoid posts but slow and clicks when using the starter button after installing a new solenoid?

Just a thought..Not sure on the 750, but other bikes have the starter and horn pushbuttons grounding directly to the controls -> handlebars/cables -> frame/motor. Cleaning up any places where this circuit might be crusty might make a difference.

Spanner 1 · « **Reply #23 on:** December 15, 2011, 09:19:12 AM »

Wrong coils !!!!!..... the 'old' set-up worked as the poor ground connection ( before you worked on the bike, paint etc. ) ADDED impedance to the coil primaries taking them up to somewhere nearer the stock 5 ohms.... I bet they are actually under 1 ohm coils ( later sportbike, electronic ign. ) and will not produce spark while the starter is demanding it's amperage.
Swing them by their H.T. leads in a rapid circle above your head and release . Enjoy the splash as they enter the lake water....

..... now start over with new/used 5 ohm coils

wrenchmuch · « **Reply #24 on:** December 15, 2011, 10:45:38 AM »

I don't know what impedance your coils are . The symptoms you describe point to a drop in voltage in the harness between the battery and the coils . As suggested before confirm that the battery is in good shape ( I know its new but there still may be an issue ) . Get it tested and then charge it over night out of the bike . After resting for a few hours a fully charged lead acid in good shape should read 12.6 - 12.75 volts ( gel 12.9 - 13 ) . 12.5 - 12.55 ( 12.6 gel ) is only 80 % charged . Once the battery is confirmed as good you can probe the harness . Put the battery in the bike and turn the key on . I'd disconnect the lights and coils to reduce load on the battery . Use a meter and connect negative lead to battery negative . Connect positive to battery positive and note voltage . you can now move the positive test lead to positive terminals all over the bike and test them one by one . Ideally you will see the same voltage at the + wire connected to coils as you will at the battery . If there's a big difference then there's a bad connection . Kill switch , key switch , bullet connectors can all be culprits . The harness is 30+ years old now and oxidation in connections can cause all sorts of trouble . Resistance in connections causes heat as well melting insulation . Old fuse holders oxidize and can cause the fuse in them to fail from heat (melts the solder in the fuse . Just pulling connections apart during the re build could have caused this problem .
Good luck
Mike

crazypj · « **Reply #25 on:** December 16, 2011, 07:58:03 AM »

Did you check battery voltage while cranking? (just put meter on battery and crank away

)
I used to teach people to remove lead going to starter and check output voltage from solenoid, sometimes the results are real surprising. (voltage tests are always surprising

)
I measured 318 peak volts on the 12v side of a Suzuki Intruder at about 5,000rpm

(you need a peak voltage adapter for meter)

grcamna2 · « **Reply #26 on:** December 17, 2011, 10:17:06 PM »

+1 on what wrenchmuch said...& make sure the coils are the correct impedance(ohms) for your application along w/ the correct plug caps;also your right handlebar switch starter button contacts may need to be cleaned.

crazypj · « **Reply #27 on:** December 18, 2011, 07:42:11 AM »

Bar contacts are either working or not working, if solenoid clicks, starter button is working and supplying enough voltage to operate.The solenoid internal contacts may be burned, there is a plastic stopper inside which limits movement and causes the 'click' when it bottoms/tops out.
Thats why I said to check battery voltage when cranking, plus, check output voltage to starter with lead disconnected (I would also do a load test to starter, should be around 40~50 amps draw)

Spanner 1 · « **Reply #28 on:** December 18, 2011, 04:47:56 PM »

PJ....... he already changed-out the solenoid with the same results. The bike will crank the starter fast when the solenoid terminals are shorted. It's not the solenoid, it's those 1 or 2 ohm coils hogging loads of amperage as soon as you turn the key on and leaving nothing for the starter..... makes sense to me !.....by shorting the solenoid your 'taking back' the power from the coils and sending it to the starter........ install 5 ohm coils, problem gone.

josephus · « **Reply #29 on:** December 19, 2011, 08:08:25 AM »

sounds to me wiring try running the solid black wire to power the coils instead of the black and white one . caution engine stop button may not work. also for a more powerful spark get some old vw plug wire caps and put on as they have no resisstors in them like the factory honda ones do. if you have an old one pop it apart the resistor looks like a round fuse.

crazypj · « **Reply #30 on:** December 19, 2011, 09:29:44 AM »

Quote from: Spanner 1 on December 18, 2011, 04:47:56 PM

PJ....... he already changed-out the solenoid with the same results. The bike will crank the starter fast when the solenoid terminals are shorted. It's not the solenoid, it's those 1 or 2 ohm coils hogging loads of amperage as soon as you turn the key on and leaving nothing for the starter..... makes sense to me !.....by shorting the solenoid your 'taking back' the power from the coils and sending it to the starter........ install 5 ohm coils, problem gone.

I guess I miss-read something?
There is less resistance to solenoid, starter 'robs' power from coils, not the other way round.
Is it a 'new' new solenoid or just 'new' to the bike?
There is no harm in doing the tests I suggested, in fact it proves if solenoid is good or bad.
Even new parts can be faulty 'out of the box' (unusual but it happens)
As we are not 'there' to 'see' exactly whats going on, we need to eliminate variables
It could be the new battery, has it been load tested yet?
It may well be wrong coils, wrong leads, wiring completely messed up and various things connected wrong.
It is a real simple circuit, no 'computers' controlling anything so it should be simple to fix
I'm bored with this thread now and really don't want to argue with people trying to help OP

Spanner 1 · « **Reply #31 on:** December 19, 2011, 11:07:18 AM »

I'm bored with it too

... especially since the OP hasn't bothered to come back to his own thread since Dec. 8th.!!!!

TwoTired · « **Reply #32 on:** December 19, 2011, 11:26:42 AM »

Quote from: crazypj on December 19, 2011, 09:29:44 AM

I'm bored with this thread now and really don't want to argue with people trying to help OP

That is the way of the new "modern" forum, it seems. Facts and logical science be damned, "looks" and what "feels" right is vogue.

josephus · « **Reply #33 on:** December 19, 2011, 12:08:20 PM »

let me know how the witching the wire goes if i am wrong i am wrong but if im right it should fire up

crazypj · « **Reply #34 on:** December 19, 2011, 03:28:49 PM »

Hi TT,
As Spanner 1 noted, OP hasn't been back to give any feedback, thread is now just a discussion about what and where to check

AndyJ · « **Reply #35 on:** February 12, 2012, 02:42:40 PM »

Hey guys,
Thanks for all of the input and advice, I realize I haven't visited the forums in sometime. Been having issues in other areas which seemed to be of greater importance, like getting the bike to actually run. I will certainly check into the starter and wiring when time permits. Just kicking it for now...
It's been a challenge juggling my two young boys and and working full time. Progress on the bike has been slow. The knowledge I've learned here is invaluable and appreciated.
Still have a lot of plans for the bike, and cannot wait to complete.
Warest Regards from FL,
Andy

Spanner 1 · « **Reply #36 on:** February 12, 2012, 07:14:43 PM »

Andy... it's all good!... thanks for posting and very best of luck with your life issues, that's life iddinit ?
Ask a new Q any time your ready, good luck

wrenchmuch · « **Reply #37 on:** February 13, 2012, 06:26:05 AM »

Andy
Electrical issues will often keep the bike from running . When troubleshooting start with spark first then move to fuel . Electrical issues will often masquerade as fuel issues ( for instance a weak spark can make your plugs look like the fuel mix is rich) .
Good luck

Rigid · « **Reply #38 on:** February 13, 2012, 07:57:15 AM »

Want to test your battery in real world conditions and know exactly what it is doing in YOUR bike? Charge it overnight, push the start button to engage the starter with a voltmeter attached to the battery terminals. If it drops below 11 volts under load, the battery cannot deliver enough amperage and is faulty. Another issue that is less likely is the starter is drawing excessive amperage due to internal failure or external overload. Rock on.

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Author Topic: Please help..weak spark and only when letting off starter (Read 8547 times)