Topic: Senior project for high school - 78 CB750K

[calj737]

Can you shoot a picture of the connection of the 1/4 coil where you crimped/attached the BLK/WHT and RED please?

[madmtnmotors]

Or a bad Pamco trigger/sensor for 1/4. Switch the Pamco ignition trigger connections to the coils (swap 2/3 green with 1/4 green) and see if the spark follows. If it does, then the Pamco pickup is bad. If the spark stays on the same cylinders then the coil is bad.

[Restoration Fan]

Can you shoot a picture of the connection of the 1/4 coil where you crimped/attached the BLK/WHT and RED please?

[calj737]

And both coils are wired the same way? If so, and you're comfortable it's wired correctly, (appears so in pictures and from your description) then follow Wilburs steps to determine where the fault is.

[NobleHops]

Ya, you've chased and wired it perfectly. Follow Wilber's suggestions and you will know for sure where the problem lay.

N.

[madmtnmotors]

The male bullet connector (with the red and black/white wires) is not crimped. Did you solder that one?

Also, if you follow my suggestion and determine the coil is good, you might still want to check the wire from the coil down to the trigger (at the points plate) and make sure you have a continuous circuit before deciding the trigger is bad.

[Restoration Fan]

Wilbur,
I re-did that connection after taking the picture because it didn't appear to be very solidly in there.  I put a new bullet connector on and crimped it down well.

So....it appears I have a bad 1/4 coil.  Before swapping them, I confirmed again that I had spark on 2/3 but not on 1/4.  Then, we swapped the green/blue connections.  Afterwards, I'm still getting spark on 2/3 but not on 1/4. 

I suppose the best thing now is to try and send a PM to Pamco Pete and see if I can get a replacement coil?

[Stev-o]

 I confirmed again that I had spark on 2/3 but not on 1/4.   Afterwards, I'm still getting spark on 2/3 but not on 1/4. 

Ron - is this a typo?

[calj737]

I confirmed again that I had spark on 2/3 but not on 1/4.   Afterwards, I'm still getting spark on 2/3 but not on 1/4. 

Ron - is this a typo?

No, it means coil B is firing whether it's attached to Blue or "Yellow". Which tells me it's not the coil, but the trigger.

[Stev-o]

I confirmed again that I had spark on 2/3 but not on 1/4.   Afterwards, I'm still getting spark on 2/3 but not on 1/4. 

Ron - is this a typo?

No, it means coil B is firing whether it's attached to Blue or "Yellow". Which tells me it's not the coil, but the trigger.

That's what I was thinking - not the coil.  "Coils rarely fail" as they say...

[Restoration Fan]

Ahhh...yeah I see where my logic was bad now.  Crap.  I was hoping it was the coil because I still have the 2 coils I pulled off the bike before and could substitute one of those. 

I bought the PAMCO from VintageCB750.com.  I guess I need to get in touch with them tomorrow and get a new one shipped out asap.  Logan has his "stand and deliver" tomorrow, which is his presentation to just his teacher.  We wouldn't have used the bike for that anyway and just used the PowerPoint.  But his final presentation is a week from today (next Wednesday) so I'm hoping that they can get me one shipped out overnight.

Worst case, we can trailer it up there and just let them look at it without cranking it.  But it sure would be nice to be able to let them hear it crank.

[calj737]

Just for giggles, inspect very closely the ignition plate. Any chance a red wire is grounding out or is damaged at the connection?

[Restoration Fan]

It doesn't appear so, cal.  The connections aren't in a bind and look to be very solid.  And I can't see where it would be shorting against anything either.  Where it passes through the hole, the wire is in good shape and doesn't look to have any tears.

[Maurice]

Have some points laying around? They're not that hard to set up, in the meantime...

[calj737]

More proof that you and Logan are 1:1,000,000. Probably the only folks I've seen receive a effective Pamco unit. Rotten luck, but I think your diagnosis is conclusive.

Stella has her groove on for sure-

[evanphi]

Damn! FYI, vintagecb750 is based in Canada, while cb750supply is based in the US. You might be able to return this set to vintagecb750 and order a new one faster from cb750supply. They are essentially all the same stuff.

[Restoration Fan]

Damn! FYI, vintagecb750 is based in Canada, while cb750supply is based in the US. You might be able to return this set to vintagecb750 and order a new one faster from cb750supply. They are essentially all the same stuff.

Good info.  Thank you.  I'm going to call them tomorrow and see what's available.  I don't mind them charging my card for a new unit and then refunding it when they get my unit back if that will help speed things up.

Thank you to all of you guys for the insight and the help with diagnosing what's going on.  We really appreciate the support, advice and help that we have received from other members of this forum. 

[madmtnmotors]

I confirmed again that I had spark on 2/3 but not on 1/4.   Afterwards, I'm still getting spark on 2/3 but not on 1/4. 

Ron - is this a typo?

No, it means coil B is firing whether it's attached to Blue or "Yellow". Which tells me it's not the coil, but the trigger.

Now I'm confused.  If you connect trigger (points) "A" (or blue) to coil "B" and the coil fires, and then you connect trigger (points) "B" (or yellow) to coil "B" and the coil fires again, then that means both triggers are good (they both signal the coil to "fire"). Connect each set of triggers (one at a time) to coil "A" only and see if coil "A" will fire on either set of triggers. If coil "A" will not fire on either set of triggers then the coil (or it's connections) are bad.

Now I'm getting a headache... 

[madmtnmotors]

Wilbur,
I re-did that connection after taking the picture because it didn't appear to be very solidly in there.  I put a new bullet connector on and crimped it down well.

So....it appears I have a bad 1/4 coil.  Before swapping them, I confirmed again that I had spark on 2/3 but not on 1/4.  Then, we swapped the green/blue connections.  Afterwards, I'm still getting spark on 2/3 but not on 1/4. 

I suppose the best thing now is to try and send a PM to Pamco Pete and see if I can get a replacement coil?

This points to a bad coil to me...

[Retro Rocket]

Pm Peter, he'll sort you out...

[calj737]

Wilbur,
I re-did that connection after taking the picture because it didn't appear to be very solidly in there.  I put a new bullet connector on and crimped it down well.

So....it appears I have a bad 1/4 coil.  Before swapping them, I confirmed again that I had spark on 2/3 but not on 1/4.  Then, we swapped the green/blue connections.  Afterwards, I'm still getting spark on 2/3 but not on 1/4. 

I suppose the best thing now is to try and send a PM to Pamco Pete and see if I can get a replacement coil?

This points to a bad coil to me...

I'm confused, Wilbur.

Coil A is connected to 1/4 and BLUE, but does not fire
Coil B is connected to 2/3 and GREEN, and does fire.
Move GREEN to coil A and 2/3 still fire (proof that coil A fires)
Move BLUE to coil B and 1/4 still won't fire.

Gotta be the triggers, no? Coils when wires swap problem follows the wire, not the coil.

Or am I missing something?

[madmtnmotors]

I'm confused, Wilbur.

Coil A is connected to 1/4 and BLUE, but does not fire
Coil B is connected to 2/3 and GREEN, and does fire.
Move GREEN to coil A and 2/3 still fire (proof that coil A fires)

Wrong. Coil A is still connected to 1/4 spark plugs, only now we're connected to the 2/3 trigger. you've only swapped triggers, not spark plug leads. We've proved that both triggers will "fire" coil B (still connected to cylinders 2 and 3). They are now out of time, because we are firing out of sync, but we've shown that both triggers will fire coil B. 

[Restoration Fan]

Wrong. Coil A is still connected to 1/4 spark plugs, only now we're connected to the 2/3 trigger. you've only swapped triggers, not spark plug leads. We've proved that both triggers will "fire" coil B (still connected to cylinders 2 and 3). They are now out of time, because we are firing out of sync, but we've shown that both triggers will fire coil B. 

That's correct.  I didn't swap the spark plug leads; just the triggers.   As a matter of fact, I'll admit to a little cheat.  Rather than taking the time to actually unscrew the spark plugs, I took another spark plug I had and just popped the spark plug wire off the plug that was still in the hole.  Then, I'd connect it to the extra plug and use that to test the wire.  Saved me a bunch of times of unscrewing the #2 and #3 plugs...which are a pain in the wompus to take out.

[madmtnmotors]

So hook up that spare coil and start that puppy! 

[calj737]

Yup, you're dead right, as usual Wilbur. Thanks for pointing that out.