Topic: Poor Idle, Hesitating acceleration, and Pipe backfire oh my... K7 CB750

[beerme351]

I've finally got some time today to put in on the bike.  Pulled airbox, and I'm not getting anything but a dribble from the accelerator pump.  I'm feel good about the passage being clear, so going to chase down the accelerator pump clearance along with choke clearance. 

Last time, I had the bowls off I left them at 12 mm height, but might hold off on changing since the accelerator pump is currently a glaring issue. 

 Going to also clean the uni foam filter and let dry for hours and hours👍

While carbs are off I'll verify slo jets are clear as well and report back. 

Thanks everyone

[beerme351]

Ok, some progress.

Pulled carbs and verified float level on carbs.  All but #2 were at 12.5 mm.  #2 was probably closer to 13 mm, so I set this down to 12.5mm.  Verified all jets were clean, they were clear, but did clean them for good measure. 

Verified Choke fully close setting by manual and visually (pulled choke out fully, turned adjusting screw until hit stopper, then closed choke and turned screw in 2.5 turns)

Thoroughly went through accelerator pump following this procedure: 
http://forums.sohc4.net/index.php/topic,167028.msg1931968.html#msg1931968


Bench verified all accelerator nozzles are pumping, good to go.

Cleaned and dried uni filter for several hours (6 hours).  Reinstalled carbs and air box...started right up, idling well off choke.   I did not get a chance to take her out for a ride, will do that tomorrow, but did notice some serious sparking between the points and the advancer plate have  returned.  Please see videos below and let me know your ideas. 


https://i.imgur.com/MQhjGnh.mp4


https://i.imgur.com/W71Jrhj.mp4

[RAFster122s]

Chinese condensers?

[beerme351]

Chinese condensers?

Makes the most sense, got a good line on quality ones?

[enwri]

In the second video, it looks like it's arcing between the side of the spring and the inside of the contact arm. They are both supposed to be the same potential seeing how the spring is riveted to the arm.
Has the riveted join between the arm and spring failed to an open circuit somehow? and is it now using the spring touching the side of the arm for continuity instead?

 I've only ever seen sparks from points coming from the points contacts themselves.

[beerme351]

Good question, I'll look into that later.  I do have a spare set of points to try. 

Anyone have experience with K&S condensers?  I'm coming up empty for the TEC brand

https://www.denniskirk.com/k-and-s/ignition-condenser-2105-0123.p42615.prd/42615.sku

[Stev-o]

Good question, I'll look into that later.  I do have a spare set of points to try. 

Anyone have experience with K&S condensers?  I'm coming up empty for the TEC brand

https://www.denniskirk.com/k-and-s/ignition-condenser-2105-0123.p42615.prd/42615.sku

Is that a Harley part?

[beerme351]

I don't believe so. "30250-300-154" is the Honda number and these are the cb750s listed in the fitment tab. "CB750K 1969-1970, 1972-1978"

[beerme351]

Ok new condensers came in and same issue, stray spark between points and advancer plates.  Any pointers? (pun intended)

I have checked points to ground and no short present when opened.  Condensers don't measure shorted. 

Really struggling to find quality points/condensers on the internet.  I have called my local Honda dealer, and doesn't sound like Honda offers alternatives anymore.

Is it safe to assume going to electronic ignition is the way to go?

[RAFster122s]

Electronic ignition won't fix a problem not caused by points plate assembly, if that is the issue. Can't really see clearly the points to clearly ID where it is sparking, point to point... Viewing the end showing the points contacts while running.
Presume you have checked assembly and distance between contractions and points plate. You are dealing with high voltage , so sparks jumping are a function of distance between points it is jumping to a certain extent.
Tough to determine condenser health without a capacitance meter as most dvms cannot do that testing.
Diachi condenser have had many instances of being bad out of the box, really crappy Chinese quality part. Their points often cannot be timed either

[beerme351]

Electronic ignition won't fix a problem not caused by points plate assembly, if that is the issue. Can't really see clearly the points to clearly ID where it is sparking, point to point... Viewing the end showing the points contacts while running.
Presume you have checked assembly and distance between contractions and points plate. You are dealing with high voltage , so sparks jumping are a function of distance between points it is jumping to a certain extent.
Tough to determine condenser health without a capacitance meter as most dvms cannot do that testing.
Diachi condenser have had many instances of being bad out of the box, really crappy Chinese quality part. Their points often cannot be timed either

RAF - if you click on the link of the second video a large video will pop up and help with seeing the arcing.  Several small arcing between the points and the plate, but most dramatic is between the spring and the points and spring and plate.  I have verified the rivet is still in tact and the spring has continuity to points ends unless the points open and the spring is verified isolated from the other side of points.

I have not checked the advancer plate assembly distance between contractions and points plate.  I'm assuming this is the shop manual?  (I'm at work and don't have it in front of me)

Yeah, I don't have a capacitance meter.  I do have that function on my multimeter, but the results are very erratic.  That's what I keep hearing from about the condensers and points, I've had zero luck sourcing from a known good Japan manufacturer...even to help eliminating these as a variable.

[HondaMan]

Currently, Honda is selling the entire points plate assembly, with TEC points and condensors (clearly marked as TEC parts, too). If there are no brand marks on the condensors or points, they are Daiichi if you bought them in the last 5 years.

My Transistor Ignition can help with the condensor problem if you can't find good ones, in that it will run with the condensors disconnected. Since it is electronic (and fast like lightning...) it will require that the spark advancer be in good shape: the points cam on the spark advancer (usually on the earlier ones, less so on the post-1976 versions) can become worn on its ID and the shims (which were plastic until about 1974-5) have long ago vanished. There should be at least 2 very thin shims between the points cam and the base of the spark advancer so they can rub against their respective surfaces without wearing. I make them out of brass shim stock when needed.

The other electronic ignitions out there (Dyna S, Tytronic) use huge amounts of current. Suppsedly the Trytronics' current version has limited its ON-dwell time (Dyna S has not) to be closer to the 180 degree timing these bikes are power-budgeted for, but I have heared mixed reviews about them, still.

I am somewhat concerned that you may have a shorted coil? That can make these sort of sparks.

[beerme351]

Currently, Honda is selling the entire points plate assembly, with TEC points and condensors (clearly marked as TEC parts, too). If there are no brand marks on the condensors or points, they are Daiichi if you bought them in the last 5 years.

My Transistor Ignition can help with the condensor problem if you can't find good ones, in that it will run with the condensors disconnected. Since it is electronic (and fast like lightning...) it will require that the spark advancer be in good shape: the points cam on the spark advancer (usually on the earlier ones, less so on the post-1976 versions) can become worn on its ID and the shims (which were plastic until about 1974-5) have long ago vanished. There should be at least 2 very thin shims between the points cam and the base of the spark advancer so they can rub against their respective surfaces without wearing. I make them out of brass shim stock when needed.

The other electronic ignitions out there (Dyna S, Tytronic) use huge amounts of current. Suppsedly the Trytronics' current version has limited its ON-dwell time (Dyna S has not) to be closer to the 180 degree timing these bikes are power-budgeted for, but I have heared mixed reviews about them, still.

I am somewhat concerned that you may have a shorted coil? That can make these sort of sparks.

Mark, I'm definitely interested in the your ignition. 

I'm in the middle of troubleshooting the coils and have 4.6ohms on both primary windings.  Caps are new and testing 5kohms.  I am getting 11.5 volts at both primary coil wires with ignition on.
 I'm following this procedure as I don't have the special meter http://forums.sohc4.net/index.php/topic,17711.msg184209.html#msg184209

In steps 4&5 I'm not seeing a spark at the plug gap, only at the test wire.  Think there's something up here?

[beerme351]

Another update, what I attempted to troubleshoot today.

- I noticed a ~.6 V drop between battery and load side of the fuse holder.  Replaced the connection 12V connection harness supplying the fuse blocks.  I also replaced the two pin connector coming off the starter solenoid in between the fuse block and the battery.  Got the V drop down to .27 between the battery and the load side of the fuse block. 
- Overall I am still seeing about a ~1V drop from battery at 12.5 volts and the coil wires leading to the points plate.  Seeing 11.5 at 1/4 coil wire and 2/3 coil wire
- Got a new set of coils and installed.  Coils measured 4.6 ohms on both coil primary windings, but unable to get a spark in steps 4&5 from TwoTired's procedure here:  http://forums.sohc4.net/index.php/topic,17711.msg184209.html#msg184209
- Hooking coils up to Bk/White 12V supply wire, pulling the spark plugs, grounding plugs, and bumping start to check for spark.  I am getting a spark, but it appears weak.
- Stray sparking at points to points plate still exist.
- Installed a "new" set of Japanese TB condensers, no change in the stray spark
- Pulled the advancer assembly and noticed only one shim behind the cam, and also what looked like some wear on the lower portion of the cam, but can't tell.  It also appears there has been rubbing against the crank seal and the back of the advancer plate.  After cleaning, greasing, and oiling pivot points, no change in symptom.  Pictures below.

- It looks like my issues somewhere at the coils or battery, but am at a loss.  Is a 1 V drop from battery to points coil wires to be expected?  Using TwoTired's test, if I am supposed to see a spark at the plug gap when grounding the spark plug threads and removing the "test" wire, I am definitely not seeing a spark.

Thoughts?  Any help is greatly appreciated as I feel I am getting close, but also running out of troubleshooting ideas.

[RAFster122s]

Sounds like your wiring isn't helping matters. Sometimes the connectors develop corrosion or resistance inside the crimp, but it is decades to do this. Black wire rot can cause issues too, but your values and drops don't point to the black wire rot...

[HondaMan]

Another update, what I attempted to troubleshoot today.

- I noticed a ~.6 V drop between battery and load side of the fuse holder.  Replaced the connection 12V connection harness supplying the fuse blocks.  I also replaced the two pin connector coming off the starter solenoid in between the fuse block and the battery.  Got the V drop down to .27 between the battery and the load side of the fuse block. 
- Overall I am still seeing about a ~1V drop from battery at 12.5 volts and the coil wires leading to the points plate.  Seeing 11.5 at 1/4 coil wire and 2/3 coil wire
- Got a new set of coils and installed.  Coils measured 4.6 ohms on both coil primary windings, but unable to get a spark in steps 4&5 from TwoTired's procedure here:  http://forums.sohc4.net/index.php/topic,17711.msg184209.html#msg184209
- Hooking coils up to Bk/White 12V supply wire, pulling the spark plugs, grounding plugs, and bumping start to check for spark.  I am getting a spark, but it appears weak.
- Stray sparking at points to points plate still exist.
- Installed a "new" set of Japanese TB condensers, no change in the stray spark
- Pulled the advancer assembly and noticed only one shim behind the cam, and also what looked like some wear on the lower portion of the cam, but can't tell.  It also appears there has been rubbing against the crank seal and the back of the advancer plate.  After cleaning, greasing, and oiling pivot points, no change in symptom.  Pictures below.

- It looks like my issues somewhere at the coils or battery, but am at a loss.  Is a 1 V drop from battery to points coil wires to be expected?  Using TwoTired's test, if I am supposed to see a spark at the plug gap when grounding the spark plug threads and removing the "test" wire, I am definitely not seeing a spark.

Thoughts?  Any help is greatly appreciated as I feel I am getting close, but also running out of troubleshooting ideas.

There's nothing out of the 'normal' in your symptoms (voltage drops, etc.), but the stray spark thing is odd. The only other time I saw that before (on a CB350, or it might have been a CB77 SuperHawk, both twins with 2 coils like these bikes have) was when one of the coils had bad insulation on the secondary side of the windings. It wasn't something I could detect with ohmmeter readings (we only had analog meters in those days...), and everything tested OK per the usual measurements, but (especially on a humid day, being back in the Midwest then) when the engine was running, there was sparking occasionally to the points baseplate from one of the points (the "R" side in that bike). In a dark garage, it was REAL pretty! In daylight all I could see was a slight blip of a spark, but in the dark garage it was like an aurora all around the points. For the test on that bike I just swapped coils (because they fit on either side in those bikes) and the problem (lightshow?) followed the coil, so replacing it solved that one.

If you don't have a coil, I could send you one to try? It's a new Sakura coil, one of my 'spares' that I used on my bike for a while. When you get it running again you can bring it back?

[enwri]

Does it still run if you move the spring away from the arm where it's sparking in the second video? It shouldn't be able to spark there. They are supposed to be the same potential.
Slip a bit of card between the arm and the spring.
Easy to try

[beerme351]

Does it still run if you move the spring away from the arm where it's sparking in the second video? It shouldn't be able to spark there. They are supposed to be the same potential.
Slip a bit of card between the arm and the spring.
Easy to try

Hondaman and Enwri...A bit of a breakthrough, I hope here.  I previously had swapped the 2/3 coil with no change to symptoms.  Tonight I put in new 1/4 coils with no change to the symptoms.  Next, I did notice the spring was very close to touching the side arm on the 2/3 points.  When loosening the coil wire and condenser nut on the points, I did notice the spring would torque to the side of the points and move around a bit while tightening.  Not sure if the slop in the spring is is a product of cheap points.  Keeping the spring centered (even gap between both point sides) while tightening the points nut, it is now running smoothly and the arcing appears to be gone. 

Took her out for a few miles and so far so good.  Nice idle, smooth pulling through the gears, I'm really hopeful this is all it was.  The rivet is still in tact, and secure...can't rationalize why this would matter being the same potential.  Taking the points off the bike, I can see some arcing marks from the spring to the side pivot point.  I'm stumped, can't figure out why this would occur, but moving the spring more to the middle while torqueing the points nut did seem to eliminate the stray arcing.   Crossing my fingers...time for some road miles.

[enwri]

It has to be something going wrong in the rivet end connection to the arm, open circuit/high resistance.
 Using the side of the spring to conduct power (just not very well)  to the actual points instead of the riveted joint. Giving it a wobble might have been enough to crack out any corrosion built up in that joint and make a better contact.
I imagine that set might fail again. Never know, give it a wobble every now and again.

[enwri]

Also, Hondamans ignition is the way to go. Takes all the current away from the points,they just about last forever.
Haven't had to touch them for years. Check them with a dwell meter and timing light every now and then.

[HondaMan]

I just last night experienced the same arcing trouble with a set of Japanese-made Daiichi points!
The spring is at the voltage potential (i.e., it goes to the coil) so when the points open, the coil's kickback voltage (about 400v) can jump the gap if it is close to the points' base frame - this will shorten the coil's spark, but it will still spark.

The spring is supposed to be rigidly captured by the rivet that forms the connection to the points contact itself, but we're talking Daiichi here...so, it can slide sideways a bit too close to the frame. Try this: loosen the nut that holds the 2 wire connectors to the points and remove the wires, then tighten that nut/screw to hold the spring aligned parallel to the frame of the points. Then go to your old points and steal the nuts from them, and use those to connect the wires (and connectors) to the points, This way the spring won't tend to misalign when tightening those tiny bolts.

[beerme351]

I just last night experienced the same arcing trouble with a set of Japanese-made Daiichi points!
The spring is at the voltage potential (i.e., it goes to the coil) so when the points open, the coil's kickback voltage (about 400v) can jump the gap if it is close to the points' base frame - this will shorten the coil's spark, but it will still spark.

The spring is supposed to be rigidly captured by the rivet that forms the connection to the points contact itself, but we're talking Daiichi here...so, it can slide sideways a bit too close to the frame. Try this: loosen the nut that holds the 2 wire connectors to the points and remove the wires, then tighten that nut/screw to hold the spring aligned parallel to the frame of the points. Then go to your old points and steal the nuts from them, and use those to connect the wires (and connectors) to the points, This way the spring won't tend to misalign when tightening those tiny bolts.

Thanks HM.  Unfortunately, I did toss these already, unaware of the significant quality issues around the points and condensers.  I did order some old Honda brand points off eBay, en route. 

I also had a condenser fail on me during this morning commute, not fun...and getting old.  Swapped in the parking lot and problem follows the condenser.

 You mentioned Honda sells a plate assy with points and condensers... any pointers on where to source from.   The dealership up here, isn't interested in helping.  Bike is currently stranded at my work. (I'm also interested in your ignition, shoot me an email)

[HondaMan]

I just last night experienced the same arcing trouble with a set of Japanese-made Daiichi points!
The spring is at the voltage potential (i.e., it goes to the coil) so when the points open, the coil's kickback voltage (about 400v) can jump the gap if it is close to the points' base frame - this will shorten the coil's spark, but it will still spark.

The spring is supposed to be rigidly captured by the rivet that forms the connection to the points contact itself, but we're talking Daiichi here...so, it can slide sideways a bit too close to the frame. Try this: loosen the nut that holds the 2 wire connectors to the points and remove the wires, then tighten that nut/screw to hold the spring aligned parallel to the frame of the points. Then go to your old points and steal the nuts from them, and use those to connect the wires (and connectors) to the points, This way the spring won't tend to misalign when tightening those tiny bolts.

Thanks HM.  Unfortunately, I did toss these already, unaware of the significant quality issues around the points and condensers.  I did order some old Honda brand points off eBay, en route. 

I also had a condenser fail on me during this morning commute, not fun...and getting old.  Swapped in the parking lot and problem follows the condenser.

 You mentioned Honda sells a plate assy with points and condensers... any pointers on where to source from.   The dealership up here, isn't interested in helping.  Bike is currently stranded at my work. (I'm also interested in your ignition, shoot me an email)

When you get this Ignition, don't install the Honda points just yet. Just disconnect the condensors and plug this thing in and it will fire back up again.

The 'new' Honda points, if they are NOS from before 2006, will be coated in cosmolene (or something similar) that is nearly impossible to completely remove: we were always instructed to '...clean the coating and then run the engine for 10 minutes..." in the old days. This burned off the residuals. If the new points were made after about 2006, then they MUST be run directly with the coils for 50-100 miles because they are tungsten-plated copper, not pure tungsten contacts. This all has occurred because when CFL lightbulbs pushed back the incandescent bulb production in the early 2000s era, the tungsten market collapsed and most of the world's mines shut in. Points then became copper pads, plated in tungsten. In car engines (distributor type) this break-in period takes about 15 minutes of run-time (a typical V-6 or V-8 engine opens/closes these 6 or 8 times per rev, our bikes do it once per rev), but in our bikes it takes longer, with a good condensor attached. Since you've run the existing points for a while, they will be more 'cured' than the new Honda parts - so, just wait a bit on them.