Topic: 1973 CB750 Four Coil Issue

[catlin]

My bike recently decided to run on cylinders 1 and 4 only.  I have checked spark, moved spark plugs, and checked grounds. I have ample spark on cylinders 1 and 4, but nothing on 2 and 3.  I have power from the module. After reading the forums on here, I decided that I likely have a bad coil. I switched coils and get spark on 2 and 3 when I move 1 and 4.  I just want to make sure i'm not missing anything before buying a new coil.  Any grounds I should check? And if I buy a new coil, should I go with the stock setup or something else?

Thanks for the input!

[Spanner 1]

Please explain... " I switched coils and get spark on 2-3 when I move 1-4 '.

[catlin]

By switching coils, I mean I switched the yellow and blue wires, or switched power from one coil to another.

[Spanner 1]

O.K. The 1 and 4 coil is triggered by the Blue wire from the left hand point set. If you plugged that Blue wire into the Yellow wire to the 2-3 coil and you got spark on 2-3 then the 2-3 points are not operating. Very first thing would be to shine up the 2-3 ( right hand ) points . A points file is best, but who has one of them anymore ! 400 grit paper folded over and worked on the point faces is next best thing. When they are shiny, pass a white business card ( best if soaked in carb cleaner ) thru' the points to remove any grit left by the sandpaper. Start bike. If still no running on 2-3 then it's time to set the points gap on 2-3 as the points may not be opening.

[Spanner 1]

Also, with a meter or 12v test light, with ign. 'on' and a piece of card between each point set ( i.e. to be sure they are open ), then you must have 12v between the Blue wire and ground and the Yellow wire and ground, or your test light must be lighting. Nothing disconnected for this test.

[catlin]

Thanks for the info Spanner, but excuse my ignorance. When you say to shine up the points, what exactly do mean? Is this on the coil itself?

Cheers,
catlin

[Spanner 1]

On the right side of the motor, remove the points cover ( 2 screws ) under this is the points that tell the plugs when to spark... here's a pic

[Spanner 1]

The point faces at upper right of pic open and close as the crankshaft turns as do the left hand points. Left hand points are working ( Blue wire ) but r/h points are not ( Yellow wire ). # 400 paper goes between the point faces on left. You should go ahead and shine up both point sets while your at it .

[Spanner 1]

With your left hand you can 'jab' the kickstarter and observe the cam turning and opening and closing the points ( bike in N ) , ign. 'off'.

[catlin]

Thanks for the info Spanner, i'll try cleaning up the points this afternoon and will follow up!  It is great when people use pictures.

[TwoTired]

You can avoid cleaning the points if have a voltmeter.  Closed points in run mode will have zero voltage across the point contacts,  Open points should have 12 v across them.   Only when these symptoms don't prove, is when you use a file to dress the point contacts.  Don't use grit paper as it embeds in the soft contact, reducing contact area, leading to faster burn of the points and replacement, as the grit is not conductive.

Cheers,

[pjlogue]

O.K. The 1 and 4 coil is triggered by the Blue wire from the left hand point set. If you plugged that Blue wire into the Yellow wire to the 2-3 coil and you got spark on 2-3 then the 2-3 points are not operating. Very first thing would be to shine up the 2-3 ( right hand ) points . A points file is best, but who has one of them anymore ! 400 grit paper folded over and worked on the point faces is next best thing. When they are shiny, pass a white business card ( best if soaked in carb cleaner ) thru' the points to remove any grit left by the sandpaper. Start bike. If still no running on 2-3 then it's time to set the points gap on 2-3 as the points may not be opening.

What Spanner1 said and I would add check the condenser or just replace them. 

-P.

[PeWe]

My bike recently decided to run on cylinders 1 and 4 only.  I have checked spark, moved spark plugs, and checked grounds. I have ample spark on cylinders 1 and 4, but nothing on 2 and 3.  I have power from the module. After reading the forums on here, I decided that I likely have a bad coil. I switched coils and get spark on 2 and 3 when I move 1 and 4.  I just want to make sure i'm not missing anything before buying a new coil.  Any grounds I should check? And if I buy a new coil, should I go with the stock setup or something else?

Thanks for the input!

If problems follow the coil, you seems to have found the root cause. Check if the 12V wire  (black/white) into the problem coil is OK, the wire from points to this coil is also OK on the coil side?  Blue 1:4, yellow 2:3, right?

Coils.... I remember a thread were we asked Hondaman about his coil experiences
http://forums.sohc4.net/index.php/topic,67543.msg1935921.html#msg1935921

https://www.partsnmore.com/parts/honda/cb750k/?q=coils
#17-6823

[catlin]

Thank you all for the input. I found out after removing the points cover that the rubber bushing that moves the right point up and down had dry rotted and was not allowing the point to open.  So, should I buy just new points or replace the whole kit and kaboodle?

Cheers,
catlin

[robvangulik]

That depends on what YOU are prepared to spend!
If replacing 1 set of points solves the problem....
If the other points look and work OK, and the condensers are good, it might work for years to come.

[catlin]

I guess i'm asking if I should replace the one point, but i'm assuming both since the other is likely to break apart soon?  Also, should I go ahead and do the condensers (pretty cheap kit from 4in1)?  And if I do all that, do I have to readjust the timing?  I would think with the new rubber bumper, the gap distance will change on the points.  Not sure what new condensers will do.  Do I have to loosen the nuts on the shaft to remove the points as well?

Thanks for all the info folks! Much appreciated.  If it wasn't for Spanner, I might of bought a new coil and still be in the same boat.

Cheers,
catlin

[catlin]

Also I noticed I had some pretty big sparks flying from the the functioning point during testing.  Does this indicate a new condenser is needed or is that normal?

[TwoTired]

If I understand correctly you found the points rubbing block for the points cam came apart?
I've heard of them wearing down.   But, only cheap ones disintegrate readily.  Look at the other one, same type?

If you don't know the service history of points and condenser, they are a routine maintenance item.  Renew them to reset the maintenance clock.

Yes, you will need to reset the timing.

The condensers reduce but do not eliminate the sparking at the points.  Bad coils cause excessive sparking.  Good to have spares, just in case.  If you want to skimp, examine the point contacts.  If they are pitted and worn, replace them or file them back into serviceable shape.  They were routinely replaced by Honda during warranty period at tune up intervals.  The owners manual says to inspect them every 3000 miles of operation.  The points can be dressed with a points file.  Get a file to recondition existing points. Grit paper is a no no unless you want to replace them more frequently.

I don't know what brand 4to1 sells.  If they are Diachi, shop elsewhere, better to get TEC brand.

Download the service manual.  Attacking the bike without foreknowledge is not wise.  Points can be serviced without touching the shaft.

Cheers,

[catlin]

Hello Two Tired,

I read the service manual and it says to lubricate the sponge for the points periodically.  The points I have look original, and i'm assuming no one has oiled this in a long time and likely caused them to break apart and wear.  I have looked more closely at the points and removed them easily without removing shaft bolts.  I'm going to change the condenser and both points.  What is your experience with oiling the sponge? How often do you think I should do this to prevent excessive wear?  Any advice as to how to check if my coils are going bad and causing excessive spark at the points?

Cheers,
catlin

[catlin]

Also, reading your post more closely I noticed the word "japan" and "s" and a celtic looking three point circle.  I'm assuming original and both have these.  For the condensers and coils, what would you define as excessive sparking? Mine look like arcing from an electrical outlet in a house, a small park but much larger than a spark plug.

cheers,
catlin

[catlin]

Here is the link to the points and condenser set.  Not sure on the brand, as it appears it is just called 4into1: https://www.ebay.com/itm/Ignition-Tune-Up-Kit-Points-Condensers-Honda-CB500-CB550-CB750-1969-1978/182412959127?fits=Year%3A1973%7CModel%3ACB750%7CMake%3AHonda&hash=item2a78a8dd97:g:608AAOSwnHZYb~Ps

Has a high rating though.....but i'm open to suggestions.

Cheers,
catlin

[HondaMan]

Here is the link to the points and condenser set.  Not sure on the brand, as it appears it is just called 4into1: https://www.ebay.com/itm/Ignition-Tune-Up-Kit-Points-Condensers-Honda-CB500-CB550-CB750-1969-1978/182412959127?fits=Year%3A1973%7CModel%3ACB750%7CMake%3AHonda&hash=item2a78a8dd97:g:608AAOSwnHZYb~Ps

Has a high rating though.....but i'm open to suggestions.

Cheers,
catlin

Order it from South Sound Honda. You will save $$ and a LOT of frustration. The aftermarket points made by Daiichi are a long and sad story, and a novice will likely never figure out ho to make them work right.

[TwoTired]

Hello Two Tired,

I read the service manual and it says to lubricate the sponge for the points periodically.  The points I have look original, and i'm assuming no one has oiled this in a long time and likely caused them to break apart and wear.  I have looked more closely at the points and removed them easily without removing shaft bolts.  I'm going to change the condenser and both points.  What is your experience with oiling the sponge? How often do you think I should do this to prevent excessive wear?  Any advice as to how to check if my coils are going bad and causing excessive spark at the points?

Cheers,
catlin

The cam luber is a felt pad wick.  Point cam grease is what to get for it. I used to get that at Harley Davidson.  But, any grease that will slowly bleed lube should be good.  I've used "Lubriplate" with success, too.  It just has to be non- hardening.

It's the condensers that can go bad and cause excessive point arcing and burning.  The coils last a good long time, unless attacked with a hatchet, or the lead insulation cracks.

4into1 doesn't list brand.  I'd guess they are Diachi based on the price of them.  There have been quite few posts where these have failed early and caused problems.  I've never used them myself, though.

I'd want Denso or TEC brand.  I'm stocked up so don't know where to get those these days.  Maybe at Honda?

Cheers,

[catlin]

Hello,

I contacted 4into1 and they stated, "The points and condensers are a generic branding and are made in Taiwan".  Would this indicate Diachi?

[TwoTired]

Hello,

I contacted 4into1 and they stated, "The points and condensers are a generic branding and are made in Taiwan".  Would this indicate Diachi?

Who knows?   Seems like a good guess, though.  Suppose they have generic quality control, too?  Or, are they relying on end users to perform functional and reliability testing?  Prove it failed and maybe they'll replace it with another for you to test out?  But, then there is the standard no return policy for installed electrical components, right?

Personally, I'd rather spend a bit more for known quality parts, with a good return policy, than be the seller's quality control agent.

It's your call.  Maybe you'll be lucky?

I don't really know how to assess what "generic branding" means.  I suspect they don't know who makes them, or don't want YOU to know.  Any reputable manufacturer will mark their components for source of maker AFAIK.  Imagine taking your Ford to Honda for warranty claims?   If they won't mark them for brand, what does that say about the confidence they have in the parts they sell?

Step right up! Step right up!  Get your headache right here!  You'll never find another one quite like it!


Cheers,
Lloyd