Topic: 1 and 4 firing, but not 2 and 3

[uwjberg]

ok - here's the background: '75 CB750F. finished my resto/cafe job, but it's only running on cylinders 1 and 4. new dyna coils, wires, and plugs. when i saw that only 1 and 4 were firing, then i switched the plug wire order, so the coil to 1 and 4 went to 2 and 3, and vis-versa. that made 2 and 3 fire, but not 1 and 4. i assumed the coil was bad, so i sent it to dyna, who tested it and said it's functioning normally.

just for kicks, i checked the points , and it seems like the spark to the 2 and 3 point spark is more inconsistent than the 1 and 3, but i can't be sure. i pulled cylinder 2 plug and ran the bike, grounding it to the engine - no spark. an odd thing when i hit the kill switch, though - one spark before the motor died. the funny thing is, the one spark would only happenwhen i pushed the kill switch to the up 'off' position. when i hit the kill switch down to the other 'off' position, no single spark before it died.

my question is, where do i start? is there something going on with the switch? i wouldn't think so, because 1 and 4 are running fine. it's been suggested that my stator is bad, but i have no idea about that - if it was bad, would power get to one coil and not the other?

thanks for any help or advice....

[CBGhia]

I think the first thing i would look at would be point gaps and condensers.  I recently had an  issue where it was only running on 2 cylinders and it was the points.  I swapped in a new set and WOW  runs better than ever.

Good Luck!

[HondaMan]

Most likely:
1. The 2-3 points set is not opening properly, or not closing properly. The symptom with the KILL switch indicates that they aren't opening properly. What gap are they set to? They should be about .014".
2. The condensor could be old and leaky. This makes for a "slow opening" action, which severly weakens the spark, or even stops it altogether until high RPM. This can be tested by removing it temporarily to see if manually opening and closing the points will bring back the spark.
3. If one of the sparkplugs is fouled, it will also stop both from firing.

To check: lay a plug on the head, connected to 2 or 3 spark wire, manually open and close the points with the key and KILL on, and watch for spark. You should get one for each points opening. Check also that the points wires (BLUE and YELLOW) near the oil tank are properly plugged together and the connectors are wires are in good shape. If these are broken, you will get no response from the points, but you will get one spark when switching OFF the KILL or keyswitch.

The bit about getting one spark if you switch the KILL in one direction, but not the other, is likely due to a slightly corroded KILL switch contact. It probably opens cleanly in the direction where you do get a spark, but opens erratically while sliding the other way. The latter will cause the coil to slowly discharge several times while you're moving the switch, not making much (or any) spark. After you figure out if it is the points or the points wire, then go in and clean the KILL switch contacts with some contact cleaner.

Do you know how to use a voltmeter? (And, do you have one?). The easiest test is to connect it to the 2-3 points and see if voltage comes and goes with the opeing and closing of the points. This will at least tell you if the circuit is complete, without trying to trace out the wiring harness.

[uwjberg]

thanks for the replies. the points and condensers are new, so hopefully they are ok. they are gapped to .016". maybe go closer, then?

i didn't realize that if one plug is fouled, the other won't fire. why is that? i'll check them both in that case.

hondaman- great input. i'll definitely check the points with your method. in terms of the voltmeter, yes i have one, but am still learning to properly use it. do i connect the leads to each side of the points (the arm, and the stationary portion)? if so, that would show no voltage, and when they touch, there should be power, correct?

[KingCustomCycles.com]

Check you have power to the 2-3 coil with the key on.  You can jumper power to the wire if it is dead and see if that is your problem.  The points are just switches that make and break the ground path so make sure they are doing just that. If the coils are powered but no spark, suspect a failed coil.

[fishman_Phil]

If you have just put in new points, check that the connector on the points has not turned a little and grounding on the backing plate. I have seen this happen before. Cheers

[KingCustomCycles.com]

If you have just put in new points, check that the connector on the points has not turned a little and grounding on the backing plate. I have seen this happen before. Cheers

+1 me too.

[TwoTired]

They may be newly purchased.  But, that does not mean newly manufactured.  The point contacts are not of noble metals, meaning they can oxidize and form an outer surface not of the parent metal.  The surface can be transparent and insulative.  If you burnish off that coating... they make good electrical contact.

It is also possible the manufacturer placed a coating in the parts to extend their shelf life... like a wax, or a paraffin oil coating that becomes waxy with age.

Anyway, as has been said, make sure your new points are indeed making contact.  Avoid using a silica abrasive to clean the contacts, as that leaves tiny insulative particles embedded in the surface and actually causes the points to wear faster.

Cheers,


Edit: spelling

[HondaMan]

thanks for the replies. the points and condensers are new, so hopefully they are ok. they are gapped to .016". maybe go closer, then?

i didn't realize that if one plug is fouled, the other won't fire. why is that? i'll check them both in that case.

hondaman- great input. i'll definitely check the points with your method. in terms of the voltmeter, yes i have one, but am still learning to properly use it. do i connect the leads to each side of the points (the arm, and the stationary portion)? if so, that would show no voltage, and when they touch, there should be power, correct?

Generally, I like to set them to Honda's midrange of .014" because that also tunes the dwell closest to ideal with the .024uF condensors, when at 3500-7500 RPM.

The voltmeter's (-) lead should go to the points baseplate, and the (+) lead to the little bolt where the wires tie on. When you open the points, you should see voltage (between 10.5 and 14 volts, depending on battery charge and wire & connector condition, but close to battery volts). When you close the points, it should be 0 volts. A side note: open the points with an insulated screwdriver handle or popsicle stick of wood: the kickback from the coils can be 400 volts for a millisecond, which isn't fun on your finger...

Like TT said above: sometimes these points have corrosion or cosmolene on them, making poor contact when new. If you suspect this, clean them with contact cleaner and wipe clean by sliding a new, clean, white business card in between them when closed. Avoid a spot with ink printed on it. Spin the card around a little, open the points and take it out, making sure no paper fibers get left behind (I hope you have better eyes than mine for this!). This is a good cleaning technique. Afterward, add a small drop of oil on the pivots and a dab of grease on the points cam, right next to that felt on the bottom side, to make things last longer.

[KingCustomCycles.com]

Nobles metals are easy to spot by their tiny crowns.    +1 on the business card and contact cleaner.  Points should never be filed or abrasive sanded. It is impossible to retain the factory surface treatments, if any, and also the alignment of the contact surfaces, as well as the factory surface roughness, are compromised.  If you don't have $20.00 for a new set of points you won't have a rideable old Honda very long.   

[HondaMan]

Points should never be filed or abrasive sanded. It is impossible to retain the factory surface treatments, if any, and also the alignment of the contact surfaces, as well as the factory surface roughness, are compromised.  If you don't have $20.00 for a new set of points you won't have a rideable old Honda very long.   

...unless you have one of my Ignitions. This gizmo is letting over 200 users ride for years on even old, used points, with electronic-ignition performance.   

Someday I'm gonna have to start a "How do you like your Hondaman Ignition?" thread. 

[uwjberg]

ok - so i checked the tab on the points connections, and they aren't grounding to the backing plate.

i performed the test per hondaman's instructions (thanks again). when i put the negative probe on the backing plate, and the positive on the 1 and 4 points, it reads 0 when connected, and ~25v when separated. the same test on the 2 and 3 side reads 0 when connected, and ~ 6v when apart. what does this indicate? (by the way, the voltmeter was set to the 200v setting - not sure if this is right. the next closets was 9v. i assume that the readings would still be pretty far off.)

[TwoTired]

Points should never be filed or abrasive sanded. It is impossible to retain the factory surface treatments, if any, and also the alignment of the contact surfaces, as well as the factory surface roughness, are compromised.

I've been reconditioning points for 40 years.  (Not the same set, though, as the rubbing block wears down.)   And, phone companies around the world have been doing it at their exchange centers with their hundreds of thousands of relay contacts since the telephone was invented.

Next, we'll be hearing that Hondas shouldn't be worked on at all, only replaced, since it is impossible to fix it as well as the factory made it. 

[KingCustomCycles.com]

I guess if I want to call someone using my Honda I will be all set.

[uwjberg]

any ideas where i go from here, given my test?

[KingCustomCycles.com]

I don't use a voltage test and your readings aren't making sense to me.  I use a simple test light to set the moment the points open, set the gap, and leave it at that.  I suspect you have a failed coil.  Swap the coils side to side and see if the problem follows the coil.  The probability of a failure not related to the points, connecting wires, or coil is remote.  I hope this helps.

[uwjberg]

that's a part of the problem - when i swap the coils, the other cylinders fire, so the problem does not follow the coil. i sent it to dyna, they tested it, and confirmed that it is functioning properly. i also swapped back the stock coil/wires, and the same result.

i think the test light would verify that the points are getting juice, since there is measured voltage going to the 2-3 points, just not nearly as much as the other points.

maybe wiring, then? what could allow one coil to work, and not the other? grounding, maybe? i had my frame powdercoated for my rebuild - could this be affecting some of the grouding connections?

[KingCustomCycles.com]

Powder coating is an excellent insulator.  I would run a new wire jumper with aligator clips directly from the points to the bad coil.  I would also run a jumper from the positive battery terminal straight to the bad coil.  If it is wiring, that will bypass it all and you will know which is bad.  I have a schematic I will send you showing clearly the points and coil wiring.  I just need an email address.

[TwoTired]

 If it reads 0 V with the the point closed, then the points are making good contact.  But, if the battery only supplies 12V to the system, where can you get 25V, or twice what is put into it?

I'd say we have measurement error here, and repeat the test.  Multimeters can measure many things; DC volts, AC volts, amps, and resistance.  What scale are you using?  You want DC volts for this test.

Measure the battery first.  Tell us what ohm primaries the coils have.  Verify the connections between key switch to coils and coils to points.  You can do this with battery disconnected and an ohmmeter.

Cheers,

[uwjberg]

Powder coating is an excellent insulator.  I would run a new wire jumper with aligator clips directly from the points to the bad coil.  I would also run a jumper from the positive battery terminal straight to the bad coil.  If it is wiring, that will bypass it all and you will know which is bad.  I have a schematic I will send you showing clearly the points and coil wiring.  I just need an email address.

good suggestion - i pm'd you my email addy.

I'd say we have measurement error here, and repeat the test.  Multimeters can measure many things; DC volts, AC volts, amps, and resistance.  What scale are you using?  You want DC volts for this test.

no argument here - i'm a newb when it comes to voltmeter usage. i'll have a look when i get back home. when i measure ohms between the points you mentioned, i am measuring resistance, correct? so if i get a zero (or low) value, that would mean a solid connection? what would a bad (or no) connection look like?

thanks for all the help.....

[TwoTired]

Resistance is measured in ohms. Zero ohms is perfect continuity in the connection.  High or infinity is basically no electrical connection.  Can you guess which one is better for passing current and voltage?


Cheers,

[uwjberg]

gotcha. hopefully i can get some better measurements in a couple of hours.

[uwjberg]

victory! weird cause.

i measured the volts again at the points (correctly, this time) - 11.8 on the 1-4 side, and 3.8 on the 2-3 side. measured the voltage at the coils, and got 12 on the 1-4 coil, and 8.4 on the 2-3 coil. tried jumping the connections as suggested, and couldn't get a different reading. i traced the harness from the points to the coils, and discovered a wire spliced into the blue wire powering the 2-3 coil. not sure what it's connected to (the PO had a windjammer fairing and some other junk on the bike). looks like it was drawing enough power from the coil to prevent firing. i clipped the wire and measured again - 11.6 volts. fired the bike up, and it's running like a champ.

now it's time to put the harness back together and ride!

thanks everyone for their help. king - the diagram made it much easier to diagnose the odd wire splice. thanks, bro.