Topic: 1 & 4 yes, 2 &3 no! 1976 CB750K6. Frustrating.

[Magpie]

Long day in the shop. This is the bike in my Winter Project thread. I'm puttering on it while waiting for my GL1100 carbs to be done. While the speedo shows 8900 miles I suspect it's a replacement speedo. 1 and 4 run nicely, 2 and 3 not at all. I have gone through the carbs today, made sure the clamps were all tight, installed a different points plate, replaced the 2/3 coil, checked all the connections to be sure they are connected, power to 2/3 points, spark at 2/3 plugs, gas supply is good from a portable tank. The timing light shows power to the 2/3 plugs as it flashes, timing is accurate. So, the 2/3 pipes remain cold as the 1/4's are heating up. Not sure what I am missing here. It has gas, air and spark. Battery is fully charged. It's probably something simple but I'll be damned if I can figure it out. I checked that the cam is not broken by removing the tappit caps and watching them work.
It's like 2/3 are not getting gas but 1/2 have a common supply and 3/4 does too. 1/4 are running so 2/3 must be getting fuel too.
I thought I knew these motors fairly well but I'm stumped here.
Ideas please?
Thanks,
Cliff.

[calj737]

Condensers? Try swapping the leads from the points to the coils so they fire the opposite cylinders.

[newday777]

I ran into this same thing a week ago Cliff on a K4 I was tuning for a friend(I had deep cleaned the carbs, put new coils and caps on, cleaned up the points with a points file, new plugs and swapped plugs around to test, tested wires for continuity from points to coils and still the 1/4 had hot pipes, 2/3 had cold pipes. I was scratching my hair out too.
I finally found it must have been a bad condenser on the 2/3 as I swapped out the points plate assembly (had a new plate on hand) and all was well, it fired right up.

[Don R]

 I also have one acting up like that, at first it was #2 &#3 firing but colder that #1 , I adjusted the points gap and timing and got them right, re-cleaned the carbs and now #4 is cold while the #1 exhaust is the hottest according to my heat gun. I cleaned carb 4 pilot jet again and blew carb cleaner through the air bleeds. New Denso plugs, good spark but no relief. I don't have a compression gauge that accurately works but I do have a leak down tester that I can adapt. I did a couple miles hoping the exhaust valve had a tiny something under the seat and would clean out. No luck.
 Good luck with yours.

[Scootch]

This seems to be a fairly common problem. I have a voltmeter that will measure capacitance. I measured my condensers this morning. They both read 0.39uF. I think the manual says they should be 0.24 +-10%. There is no marking on them that I can see.  At least they don't have the propeller emblem on them. 2 and 3 points were not wired like 1 and 4 were so I made 2 and 3 look like 1 and 4. Electrically I don't think it should matter but who knows 🤷 

[Magpie]

I have changed out the 2/3 coil and installed a different points plate. The timing light flashes when attached to the 2 and 3 leads so there is spark. That's what has me confused. 2 and 3 pipes are still cold so fuel must be the issue.? I went through the carbs, blew air through the passages but I'll pull them yet again but drain 2 and 3 to be sure they are getting fuel first. And pull the spark plugs again.

[calj737]

I have changed out the 2/3 coil and installed a different points plate. The timing light flashes when attached to the 2 and 3 leads so there is spark. That's what has me confused. 2 and 3 pipes are still cold so fuel must be the issue.? I went through the carbs, blew air through the passages but I'll pull them yet again but drain 2 and 3 to be sure they are getting fuel first. And pull the spark plugs again.

Sorry to be my own echo, but have you swapped the condensers? Points plate does not necessarily indicate that, nor swapping the coils.

[Magpie]

I'll do that today. Cliff.

[Deltarider]

What sparkplugs do you have? Not the R(esistor) type, do you?

[Magpie]

Not resistor type plugs. Changed the condenser for 2/3, made sure the spark plug caps were screwed in tight to the leads from the replacement coil, newer points plate, made sure 2/3 carbs were getting fuel, pushed the start button and it now runs on all 4. Good news! I have to balance the carbs.
I went to change the gasket on the oil pan to fix a small leak. Ha! Leaks worse now.
I think I'll lay the bike on it's side to do this next time. Gaskets on order.
Thanks for all your input.
Cliff.

[BenelliSEI]

Well done! Sometimes it’s good to just walk away for a few hours.

[HondaMan]

I'm searching for an alternate way to make condensors. This is becoming a big problem. Someone here (Maybe Delta? Can't remember who) has installed ceramic capacitors instead of the usual wax-paper-foil types that Daiichi (and China) can't seem to make. This should work fine so long as the capacitors can take the engine heat, otherwise they need to be remotely mounted. Honda used to mount them under the gas tank on the old twins, next to the coils: this might become the hot ticket...if using the flat ceramic type capacitors, you can use any capacitance value from 0.20uF to 0.39uF, so long as the voltage is at least 400v rated. If you use less than 0.20uF the points will arc a little too much and the coil voltage will drop somewhat at engine speeds over 5000 RPM. The "ideal" capacitance value is 0.24uF, and normal capacitors range from 0.22uF to 0.26uF (if good) from the vendors.

[Magpie]

The GL1100 is waiting for a fuel pump so it's time to get on with the K6. It's running with the usual thrashings sounds. That will soon change. I's a good survivor but my ocbd is kicking in. Obsessive compulsive behavior disease. 

Cliff.

[BenelliSEI]

Sounds and look very nice!

[HondaMan]

Boy, that's a pretty one!
Maybe I should paint mine this winter...I have new side covers that lack cracks, but need paint.

[Tracksnblades1]

Long day in the shop. This is the bike in my Winter Project thread. I'm puttering on it while waiting for my GL1100 carbs to be done. While the speedo shows 8900 miles I suspect it's a replacement speedo. 1 and 4 run nicely, 2 and 3 not at all. I have gone through the carbs today, made sure the clamps were all tight, installed a different points plate, replaced the 2/3 coil, checked all the connections to be sure they are connected, power to 2/3 points, spark at 2/3 plugs, gas supply is good from a portable tank. The timing light shows power to the 2/3 plugs as it flashes, timing is accurate. So, the 2/3 pipes remain cold as the 1/4's are heating up. Not sure what I am missing here. It has gas, air and spark. Battery is fully charged. It's probably something simple but I'll be damned if I can figure it out. I checked that the cam is not broken by removing the tappit caps and watching them work.
It's like 2/3 are not getting gas but 1/2 have a common supply and 3/4 does too. 1/4 are running so 2/3 must be getting fuel too.
I thought I knew these motors fairly well but I'm stumped here.
Ideas please?
Thanks,
Cliff.

It’s been a while but I think the gm/Delco Remy condensers were 22uf, Chrysler 25uf, Vertex/Mallory mags 28-30+uf..
They all should be 600v…

The Vertex 28uf are somewhat pricey compared to the gm/Delco or Ford/Chrysler Autolite condensers. Not sure I’ve ever had to replace a $20.00 vertex condenser though…

You should be able to look at your points to determine if you have the right uf condenser. Metal will accumulate on one of the points contacts if your uf size isn’t just right.  Too little uf will allow voltage to rise too quickly after the points initial opening. Allowing voltage to still jump across the still small point gap of the still opening points… Too big uf condenser will waste energy charging up the condenser instead of making the plug’s  spark..

[lash]

Long day in the shop. This is the bike in my Winter Project thread. I'm puttering on it while waiting for my GL1100 carbs to be done. While the speedo shows 8900 miles I suspect it's a replacement speedo. 1 and 4 run nicely, 2 and 3 not at all. I have gone through the carbs today, made sure the clamps were all tight, installed a different points plate, replaced the 2/3 coil, checked all the connections to be sure they are connected, power to 2/3 points, spark at 2/3 plugs, gas supply is good from a portable tank. The timing light shows power to the 2/3 plugs as it flashes, timing is accurate. So, the 2/3 pipes remain cold as the 1/4's are heating up. Not sure what I am missing here. It has gas, air and spark. Battery is fully charged. It's probably something simple but I'll be damned if I can figure it out. I checked that the cam is not broken by removing the tappit caps and watching them work.
It's like 2/3 are not getting gas but 1/2 have a common supply and 3/4 does too. 1/4 are running so 2/3 must be getting fuel too.
I thought I knew these motors fairly well but I'm stumped here.
Ideas please?
Thanks,
Cliff.

It’s been a while but I think the gm/Delco Remy condensers were 22uf, Chrysler 25uf, Vertex/Mallory mags 28-30+uf..
They all should be 600v…

The Vertex 28uf are somewhat pricey compared to the gm/Delco or Ford/Chrysler Autolite condensers. Not sure I’ve ever had to replace a $20.00 vertex condenser though…

You should be able to look at your points to determine if you have the right uf condenser. Metal will accumulate on one of the points contacts if your uf size isn’t just right.  Too little uf will allow voltage to rise too quickly after the points initial opening. Allowing voltage to still jump across the still small point gap of the still opening points… Too big uf condenser will waste energy charging up the condenser instead of making the plug’s  spark..

This is so far over my head I think next time I run into problems I will just go electronic!

[Stev-o]

This seems to be a fairly common problem. I have a voltmeter that will measure capacitance.

I did not think capacitors could be easily tested? Can you plz elaborate?

I have a Fluke meter but dont think it has the capability to test them.  Thx

[Scootch]

Some multimeters will do capacitance. You will have to check the manual for your particular Fluke meter. There are many brands of meters even inexpensive ones that will do capacitance. I have attached a couple screenshots of a meter that Harbor Freight has that supposedly measures capacitance. I have also included it's specs. I am not recommending the Harbor Freight meters. I have no idea if they work. I included their meter as an example. Many other brands and price ranges supposedly measure capacitance. Decide what you like, trust and fits your finances. That particular meter is around $20. Before I bet my life on any meter I would test it on volts, ohms, capacitance etc to see that it was reading properly.

[Deltarider]

Here's an easy test any multimeter can do.
1. Begin by discharging your capacitor. Simply hold its connector to its body. Done.
2. Select 20MΩ on your multimeter and contact one probe to the capacitor's connector and the other to its body. You should see the digits steadily rise till it nears 20MΩ or even says O.L or whatever symbol your meter has for infinite.
3. Disconnect probes. Now select say 20V on your meter.
4. Contact the probes again as before and you should now see whatever voltage steadily decline till it nears zero.
If your capacitor does all the above steadily, it's good.

[flybackwards]

two words: Dyna Tek...

[Deltarider]

two words: Dyna Tek...

We can see there are two words, but... could you be a bit more specific?

[calj737]

two words: Dyna Tek...

Amen.

[flybackwards]

Sorry that was a bit cryptic..

And its actually one word Dynatek. I found that the basic model mag sensor does a great job of getting out of the points and condenser game. Especially since there are many issues around quality and availability.

https://www.dynaonline.com/dyna-s-ignition-system-for-1969-1978-honda-cb500-cb550-cb750-ds1-2/

Basically zero wiring changes and not that expensive. I simply replaced the switched connection at the coils with a double Honda connection to power the unit and that and running the cable was all I needed to do. Yes it might fail at some point but so can any component. My 1977 K7 has points and a Hondaman unit which also works just fine.

[willbird]

Sorry that was a bit cryptic..

And its actually one word Dynatek. I found that the basic model mag sensor does a great job of getting out of the points and condenser game. Especially since there are many issues around quality and availability.

https://www.dynaonline.com/dyna-s-ignition-system-for-1969-1978-honda-cb500-cb550-cb750-ds1-2/

Basically zero wiring changes and not that expensive. I simply replaced the switched connection at the coils with a double Honda connection to power the unit and that and running the cable was all I needed to do. Yes it might fail at some point but so can any component. My 1977 K7 has points and a Hondaman unit which also works just fine.

is this the one that has a down side of an extremely long dwell ??