Topic: 1975 CB750 Condenser Question

[John G]

I have the part number; which is 30250-300-154.
Is there a cross reference number for any usable condensers?
Also I did as they say in the Honda manual I have to hook a battery to the condenser and then touch the end to the body of the condenser to check for a spark. I don't get a spark so I'm assuming I need new ones.

[newday777]

Beware of aftermarket condensers. They die very fast.
Use only Honda condensers.

#10
https://www.southsoundhonda.com/--xpartsstream#/Honda_Powersports/CB750KA_(76)_750_FOUR%2c_JPN%2c_VIN%23_CB750-2540001_TO_CB750-2575894/POINTS/b3d05c73-22e7-4620-b018-132301d96b6e/80fb05af-446d-41cb-a88f-21b6993df839/y

[69cb750]

Original condensers are good, aftermarket are bad
https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2323012.m570.l1313&_nkw=30250-300-154&_sacat=0
If bike runs good condensers are good.

[bryanj]

If they are relly selling the complete assembly for$89 thats a steal!!!

[HondaMan]

I have the part number; which is 30250-300-154.
Is there a cross reference number for any usable condensers?
Also I did as they say in the Honda manual I have to hook a battery to the condenser and then touch the end to the body of the condenser to check for a spark. I don't get a spark so I'm assuming I need new ones.

This was a silly (bordering on stupid) test that someone at Honda put into (many of) the manuals. In order to see the spark from a 12 volt charge you would have to be in almost total darkness when you touched the lead-to-case together to see the spark from a 0.24uF capacitor at 12 volts: you can barely see a spark from a 1,000uF capacitor at hundreds of volts!

A much better test is to run the bike in a darkened garage and watch the points for arcing. If it is a tiny spark bouncing about the contacts, the condensor is good. If there are sparks flying off like a 4th of July sparkler, the condensor is open (i.e., no capacitance) - a test you can also mimic by just disconnecting the condensor from the points and running the engine that way. If it is shorted, or 'leaky' as a partial short, the bike will struggle to run after warmup. The latter is the symptom and signature of many Chinese-made crap condensors.

[John G]

Thanks HondaMan,
The bike didn't like to idol after a 2 hour highway run. I checked the valve adjustment and the thought I would check the electrical components. Now that I've watched the university of youtube I can use my meter to check the condensers. Your explanation is also helpful and easy to perform. Again thanks. I'll put a message out when I get it figured out what's the issue with the idol.   

[Deltarider]

This video may help you diagnose a faulty condenser:

At the breakerpoints a bit of sparking is normal, excessive sparking or arcing is not good and can indicate a bad condenser. In this vid the left condensor (1+4) is bad, right condensor (2+3) is good.
Video: courtesy Ulf Penner

[bryanj]

I do not remember seeing that test in a proper Honda manual, all the one i had said to use the Honda "suitcase" tester with capacitance meter

[MauiK3]

Great little video, really shows what we need to know.

[Medyo Bastos]

If you listen closely you can hear that erratic spark from a short distance


Sent from my iPhone using Tapatalk

[HondaMan]

Excellent video, Delta! That's the best way (outside of Honda's old tester) I know of to diagnose a bad one.

[jwurbel]

Southbound has been out of that part for quite some time.  Just letting you know as I tried recently.

[trigger]

I had a condenser go last year on a CB750. No unusual sparks at the points, the bike would rev fine standing still but, would misfire under load out on the road. Can not complain as, the bike is 48 years old and it was still on the original condensers .

[HondaMan]

I especially miss the old Hitachi (and the American-made copies from Blue Streak, sold during the 1980s) condensors. They were somewhat self-healing after a long sojourn without power applied: their capacitance would fade a little to about 0.16-0.20uF, but using them for a couple of weeks would make them come back to 0.24uF or more. They were of a stiff waxed-paper core. The insulation went to polymer insulation around the late 1990s, so they either work and stay working, or they die almost as soon as they are used. The testing causes a large failure rate, from what I've heard: those that are not tested get to die in your own bike. 

[HondaMan]

I do not remember seeing that test in a proper Honda manual, all the one i had said to use the Honda "suitcase" tester with capacitance meter

The one we had never worked for condensors, from the first day we got it. I repaired it at one point (broken wiring, I think it was) but then the vibrator tube that was supposed to simulate points to run coils for their testing also quit, and we couldn't get one. It was cool when it worked, showing clearly good vs. weak coils. After that it just became a bench volt-ohm-amps meter in a suitcase.

[bryanj]

One for sale on ebay US at the moment for $200+ but missing the strobe

[Deltarider]

Excellent video, Delta! That's the best way (outside of Honda's old tester) I know of to diagnose a bad one.

Actually, it's a miracle, at least imo, the bike runs the way it does run. I mean, seen the arcing, I would have expected the engine to run way worse than it does.
Now that electronic thingies are becoming cheaper and cheaper, would any of you guys know of a thingy to test coils. What I have in mind is a device that simulates running, preferably with a switch so you can bring 'the rpm' up to 10.000. So by have it going for 15 min. you'd detect intermittent firing or even quitting and you would know your coil has aged and should be replaced.

[bryanj]

Its not the time you test ist the max gap

[Deltarider]

Its not the time you test ist the max gap

I was told that often you can start your car or bike and everything seems OK and then 10-15 minutes later a coil starts malfunctioning.

[bryanj]

Yes but having used the suitcase tester mentioned above that shows up as spark failure at a smaller gap, on the tester you increase the gap until spark failure, from memory 7mm is ok

[Deltarider]

Ok, so you referred to that suitcase (see pic), me, I referred to a big workbench I've seen in an oldfashioned workshop specialised in electric equipment, like starters, alternators, distributors, coils etc. I'm afraid these specialised workshops have dissapeared. At least the one in my neighbourhood did.

[bryanj]

I think that is just a different version of the "suitcase" tester mentioned above, either or were a requirement in Honda dealer workshops same as the special tools board and vac gauges

[Oddjob]

The part labelled service tester was for the coils IIRC. The little perspex window covered the movable poles with the dial at the bottom increasing the gap between the poles. There was a capacity tester for condensers on there as well, we used to charge them up and thrown them at other mechanics shouting catch as we did so, if they caught them they got a bit of a belt from earthing them out through their body, not a PC thing to do now but we had to make our own amusement back then  .

TBH the suitcase hardly got used, it was too much of a faff to get all the stuff out, we also had the roll cabinet one with the oscilloscope screen in it, only ever saw that used once.

[bryanj]

Ken, there were two different versions of the "suitcase" tester.
One had one analogue dial to do everything with the selector switch
The other had 2 analoge dials where the rh one did dwell, points resistance and capacitor testing, the lh one did resistance,volts,amps.
Both had the adjustable spark gap tester, not sure if both had the strobe unit.
At Meads it was screwed down on a movable cabinet at about4ft high with a car battery in the bottom to power it. I used it most weeks for something, usualy points condition, frqentlycoil test

[scottly]

What I have in mind is a device that simulates running, preferably with a switch so you can bring 'the rpm' up to 6000. So by have it going for 15 min. you'd detect intermittent firing or even quitting and you would know your coil has aged and should be replaced.

I built an ignition tester that can spin the points cam up to 10,000 RPM.

[Oddjob]

The one pictured looks to be the same as we had at Queenies Bryan.

[bryanj]

Thats what we had as well, the one on ebay is the single dial one

[grcamna2]

What I have in mind is a device that simulates running, preferably with a switch so you can bring 'the rpm' up to 6000. So by have it going for 15 min. you'd detect intermittent firing or even quitting and you would know your coil has aged and should be replaced.

I built an ignition tester that can spin the points cam up to 10,000 RPM.

That's Very nice Scott 

[Deltarider]

Wow! That's quite a machinery! I had something electronic in mind that can mimick the switching in the primary circuit up to around 167Hz (10k RPM). You could test a coil's endurance by having the HT leads like in the pic, run it for 15 min. and... create lots of ozon in the process. Aussies, here's your chance! 

[HondaMan]

What I have in mind is a device that simulates running, preferably with a switch so you can bring 'the rpm' up to 6000. So by have it going for 15 min. you'd detect intermittent firing or even quitting and you would know your coil has aged and should be replaced.

I built an ignition tester that can spin the points cam up to 10,000 RPM.

Cool!
I have a leftover servomotor somewhere around here that will go to 15k RPM (if I can find it, from the last century?). It came out of a CNC machine that got new motors in the 1990s. You can buy an inverter now for $100 that will run to 300 Hz, should be enough to get it up to 9k-ish range. Interesting testbench part, no?

The Honda tester we had was about 16" by about 14", about 9" thick/deep. It had the adjustable spark-gap tester under a window and a frequency (RPM) knob next to that. The condensor tester used the same vibrator tube (like in 1950s car radio for making their plate voltage for the tubes) inside to generate high voltage (350-ish volts) for the condensor test. That tube was the item that stopped working after just a winter's season, and we never repaired the tester because we couldn't get that tube.

[Mark1976]

What I have in mind is a device that simulates running, preferably with a switch so you can bring 'the rpm' up to 6000. So by have it going for 15 min. you'd detect intermittent firing or even quitting and you would know your coil has aged and should be replaced.

I built an ignition tester that can spin the points cam up to 10,000 RPM.

I gotta try fabbing up one of these, it is such a great idea...

[willbird]

What I have in mind is a device that simulates running, preferably with a switch so you can bring 'the rpm' up to 6000. So by have it going for 15 min. you'd detect intermittent firing or even quitting and you would know your coil has aged and should be replaced.

I built an ignition tester that can spin the points cam up to 10,000 RPM.

Cool!
I have a leftover servomotor somewhere around here that will go to 15k RPM (if I can find it, from the last century?). It came out of a CNC machine that got new motors in the 1990s. You can buy an inverter now for $100 that will run to 300 Hz, should be enough to get it up to 9k-ish range. Interesting testbench part, no?

The Honda tester we had was about 16" by about 14", about 9" thick/deep. It had the adjustable spark-gap tester under a window and a frequency (RPM) knob next to that. The condensor tester used the same vibrator tube (like in 1950s car radio for making their plate voltage for the tubes) inside to generate high voltage (350-ish volts) for the condensor test. That tube was the item that stopped working after just a winter's season, and we never repaired the tester because we couldn't get that tube.

I was doodling over the idea of using a V8 GM HEI distro, we used to hook one of the big yellow ACCEL super coils up to one of those. Spinning it with my M18 fuel drill came out to 14,400 SOHC RPM if I did my math right. The HEI distro are not as cheap and plentiful as they used to be but I think I have a couple in a box somewhere.

Bill

[Tracksnblades1]

What I have in mind is a device that simulates running, preferably with a switch so you can bring 'the rpm' up to 6000. So by have it going for 15 min. you'd detect intermittent firing or even quitting and you would know your coil has aged and should be replaced.

I built an ignition tester that can spin the points cam up to 10,000 RPM.

Cool!
I have a leftover servomotor somewhere around here that will go to 15k RPM (if I can find it, from the last century?). It came out of a CNC machine that got new motors in the 1990s. You can buy an inverter now for $100 that will run to 300 Hz, should be enough to get it up to 9k-ish range. Interesting testbench part, no?

The Honda tester we had was about 16" by about 14", about 9" thick/deep. It had the adjustable spark-gap tester under a window and a frequency (RPM) knob next to that. The condensor tester used the same vibrator tube (like in 1950s car radio for making their plate voltage for the tubes) inside to generate high voltage (350-ish volts) for the condensor test. That tube was the item that stopped working after just a winter's season, and we never repaired the tester because we couldn't get that tube.

I was doodling over the idea of using a V8 GM HEI distro, we used to hook one of the big yellow ACCEL super coils up to one of those. Spinning it with my M18 fuel drill came out to 14,400 SOHC RPM if I did my math right. The HEI distro are not as cheap and plentiful as they used to be but I think I have a couple in a box somewhere.

Bill

What kind of math was you using? Fuzzy Logic..?
My m18 only specs 2100rpm no load….
Gear box or just multiplying by 8…?

[willbird]

What I have in mind is a device that simulates running, preferably with a switch so you can bring 'the rpm' up to 6000. So by have it going for 15 min. you'd detect intermittent firing or even quitting and you would know your coil has aged and should be replaced.

I built an ignition tester that can spin the points cam up to 10,000 RPM.

Cool!
I have a leftover servomotor somewhere around here that will go to 15k RPM (if I can find it, from the last century?). It came out of a CNC machine that got new motors in the 1990s. You can buy an inverter now for $100 that will run to 300 Hz, should be enough to get it up to 9k-ish range. Interesting testbench part, no?

The Honda tester we had was about 16" by about 14", about 9" thick/deep. It had the adjustable spark-gap tester under a window and a frequency (RPM) knob next to that. The condensor tester used the same vibrator tube (like in 1950s car radio for making their plate voltage for the tubes) inside to generate high voltage (350-ish volts) for the condensor test. That tube was the item that stopped working after just a winter's season, and we never repaired the tester because we couldn't get that tube.

I was doodling over the idea of using a V8 GM HEI distro, we used to hook one of the big yellow ACCEL super coils up to one of those. Spinning it with my M18 fuel drill came out to 14,400 SOHC RPM if I did my math right. The HEI distro are not as cheap and plentiful as they used to be but I think I have a couple in a box somewhere.

Bill

What kind of math was you using? Fuzzy Logic..?
My m18 only specs 2100rpm no load….
Gear box or just multiplying by 8…?

2100 rpm times 8 is 16,800. The SOHC fire once per crankshaft revolution, the HEI distro fires 8x per revolution ? So 2100 drill rpm is 16,800 sparks per minute.

I used 1800 drill rpm to get the 14,400 number...the 1800rpm was a number I googled up....I see some different specs for different models.

[Tracksnblades1]

What kind of math was you using? Fuzzy Logic..?
My m18 only specs 2100rpm no load….
Gear box or just multiplying by 8…?

2100 rpm times 8 is 16,800. The SOHC fire once per crankshaft revolution, the HEI distro fires 8x per revolution ? So 2100 drill rpm is 16,800 sparks per minute.

I used 1800 drill rpm to get the 14,400 number...the 1800rpm was a number I googled up....I see some different specs for different models.
[/quote]

Wouldn’t a Vega/Monza 4cylinder Hei with the reluctor and pickup mounted on the end of the shaft/case be a little easier.. then just 1:1…  The old rotor, cap, internal/external coils aren’t missed by many…

If you’re planning a dual plug head for the sohc750, I’m all ears and all in…😁

[willbird]

This was in relation to testing ignition coils, not running a bike.

[HondaMan]

Its not the time you test ist the max gap

I was told that often you can start your car or bike and everything seems OK and then 10-15 minutes later a coil starts malfunctioning.

My brother's CB500 Four suffered that one summer (1977, I think it was) after we had toured the American West just east of California for over 2 weeks together. After we got back to Denver he rode on across Kansas (100+ degrees each day) and the 500 would not rev above 4400 RPM after 15 minutes or so of runtime. He stopped at every Honda shop he could find along the I-70 corridor, buying parts: new points plate, new plug caps, new sparkplugs. He finally just rode it home 15-20 minutes at a time (4 days to cross Kansas to central Missouri!). About a week later he realized he never tried the coils: new Honda coils fixed it immediately.

[Deltarider]

Its not the time you test ist the max gap

I was told that often you can start your car or bike and everything seems OK and then 10-15 minutes later a coil starts malfunctioning.

I once walked into a workshop dedicated to testing electric automotive parts like starters, alternators and the like. It was an oldfashioned workshop, a 10 min walk from where I lived, with big oldfashioned analogue gauges. I was there to ask something for my yacht's alternator. In the background I heard a high tone and mixed with the smell of electric gear, I also sensed ozon. When we walked towards the bench where the sound came from, I saw an automotive coil being tested. The man explained the ultimate test for a coil is running it for some 15 minutes.
I remember I once have asked Ashimoto (UK forum) this, but he never came with an answer.
Hence my question if nowadays there maybe is a cheap electronic device that can mimick the primary circuit. Would be great if we could evade all these posts about coils for once and for all.

[willbird]

Its not the time you test ist the max gap

I was told that often you can start your car or bike and everything seems OK and then 10-15 minutes later a coil starts malfunctioning.

I once walked into a workshop dedicated to testing electric automotive parts like starters, alternators and the like. It was an oldfashioned workshop, a 10 min walk from where I lived, with big oldfashioned analogue gauges. I was there to ask something for my yacht's alternator. In the background I heard a high tone and mixed with the smell of electric gear, I also sensed ozon. When we walked towards the bench where the sound came from, I saw an automotive coil being tested. The man explained the ultimate test for a coil is running it for some 15 minutes.
I remember I once have asked Ashimoto (UK forum) this, but he never came with an answer.
Hence my question if nowadays there maybe is a cheap electronic device that can mimick the primary circuit. Would be great if we could evade all these posts about coils for once and for all.

Many devices can generate a 5V logic level signal.



Many modern coils have an "igniter" included that will let you drive them directly with that signal. You can also buy that Bosch igniter as a separate part and use it to drive any kind of coil.
There are some OEM parts avail that can be used as coil drivers


But this will work and is way cheaper :-).

https://www.diyautotune.com/product/coil-driver-kit/

many folks in the tuner ECU community will increase dwell time until the coils start to get warm and then back off a bit.

You can buy an arduino clone for about $10, then buy the coil driver kit above and rig up a tester for $20, I was able to borrow the scope from work.

But a junk blown up lawnmower engine that the crank still spins on would give you a set of points you could operate at any rpm too ;-).