Topic: Senior project for high school - 78 CB750K

[Restoration Fan]

What are you going to do with those?

I told Randy that I would send them back to him when I receive the proper ones.

[Restoration Fan]

We removed the #1 spark plug and tried to crank it today.  After hooking the plug back up to the spark plug wire and starting the motor, we held the spark plug to the engine casing and we didn't get spark at all.  So we're thinking the issue might be spark and not gas.  (Smart, huh?  ).  We're using a PAMCO ignition system and new PAMCO coils.  We wired them up according to the online instructions, but I supposed it's possible that we don't have those set up correctly.  If I'm thinking straight, not getting spark would likely indicate a problem between the coils and the spark plug.  Correct?  Because the battery is still showing over 12 volts.

Also, we are definitely getting gas through to it.  I put clear lines on from the tank to the carb and gas is flowing through it.  If you keep twisting on the throttle, you can actually make it piss gas out of the overflow lines beneath the bike.  Is that normal or does that signify that the floats aren't adjusted properly?

[calj737]

Confirm you have 12v at the coils, and after the KILL switch. Do you have spark on 2/3?

[vfourfreak]

If you have gas coming out of anywhere, please be careful testing for sparks !! Wait till any gas has evaporated and keep the workshop well ventilated.

Kev

[70CB750]

The gas should not be coming  out of bowls, floaters are supposed to stop it.

Kill switch is in run position?

[Restoration Fan]

I think I have them adjusted to the improper height then because gas was coming out of all 4 overflow tubes. 

Once we saw that, we stopped the testing of the spark because I tend to like my eyebrows where they are...still on my face.  It may be time to take them off the bike and run them with me over to Bill Benton's house to see if he can help me get them all adjusted correctly.

We didn't get a chance to test the spark on #2 or #3 or to confirm 12V after the kill switch due to the need to work on AP Calculus.  By the way, how would you test that you have 12V after the kill switch?  Take the headlight back off and test one of the wires there?  The only other way I can think of would be to remove the screws and take the kill switch assembly off the handlebars and test it internally there.

[ivanhoew]

ron , with the switch set to run ,see if there's a live 12v  at the coils .

robert

[calj737]

Your coils should have a BLK/WHT wire connected to a screw on each coil. This carries switched 12v for the ignition. This become BLK/WHT from the right handle bar, originally BLK and jumpered at the KILL.

Place your meter on the coil screw and ground to the frame. RUN position, key on. Measure the voltage. No sparks, no running motor needed. And you can do this before you disassemble the carbs.

If you have 12v in each coil at this screw, then you should have spark at each cylinder. Got to continue your search for electrical mishaps. But it's a simple test and tells you heaps about where to look for the problem.

[70CB750]

Check the voltage on the black with white wire at the coil.

On my build I used a timing gun/light to check for spark.  Cranking the engine with starter and getting strobo flash for every spark plug wire - and none for the Kill swith to Stop.

[evanphi]

Confirm you have 12v at the coils, and after the KILL switch. Do you have spark on 2/3?

Was also going to suggest this... 12V at the battery can be lost very quickly by the time it gets to the coils!

[70CB750]

My Pamco is wired from the kill switch too, btw.

[Restoration Fan]

My Pamco is wired from the kill switch too, btw.

Did yours come with two of the same coils?  The instructions listed online said in step 5:

5. With the trigger magnet positioned as shown above, the green wire from the trigger on the right goes to the coil for cylinders 1 and 4 (blue wire), and the other green wire goes to the coil for cylinders 2 and 3 (yellow wire). If you assemble the rotor with 2-3 in place of 1-4 as shown, then you can either do it again, or just reverse the wires for each cylinder.


But we don't have a yellow wire coming from either coil.  Instead, both of the coils they sent us have blue wires.  Not that it should really matter, I wouldn't think.  So we used that other blue wire instead of the yellow wire.

[evanphi]

The colour from the coils shouldn't matter... as long as the wire connecting TO the 1/4 coil is blue, and the one going to the 2/3 coil is yellow.

[70CB750]

He has generic wires on coils is what I understand.

No, it would not matter, it would still produce a spark even if the spark was on wrong time of the cycle for given pair of cylinders.

[calj737]

Colors don't matter, blue, yellow, pink or purple... What does matter is: the stock "blue" wire serves the coil for 1/4 and the stock "yellow" wire serves 2/3. This provides accurate timing fire of the coils.

But you still have to resolve the 12v issue. Even if you had the coil signal wires (blue, yellow, pink, green) reversed, you'd have spark, but crappy timing. Look for the BLK/WHT.

Prokops point was that he uses the stock KILL switch inline with the pamco successfully to interrupt the ignition via the KILL switch for safety, as you should. But, in order for your coils to fire, the KILL switch must be on, and if you've used the stock BLK/WHT scheme, then it must be carrying 12v to the coils.

[70CB750]

But you still have to resolve the 12v issue. Even if you had the coil signal wires (blue, yellow, pink, green) reversed, you'd have spark, but crappy timing. Look for the BLK/WHT.

Thanks Cal, I always remind myself how much I would suck as a teacher when I am trying  to explain something 

[calj737]

Sometimes I write too much, but I suspect when explaining something someone is reading, they may not fully picture what is being written. Best to take them step-by-step when helping them through "new territory".

And, it's often likely that my explanations are already obvious to the reader, so I'm just prattling on-

[NobleHops]

Sometimes I write too much, but I suspect when explaining something someone is reading, they may not fully picture what is being written. Best to take them step-by-step when helping them through "new territory".

And, it's often likely that my explanations are already obvious to the reader, so I'm just prattling on-

Bollocks, your explanations are among the clearest and most helpful of anyone's, and so referencable for other people's projects too.

[NobleHops]

Ron,

You're so close! You've done an amazing job, no doubt learned a ton that will be applicable to any future moto projects, and shared an experience with your son that I, for one, can only envy.

You're closer than you think, and this chronicle has been fantastic reading, and a great resource for others in the future. Great job.

Nils

[iron_worker]

I verified a set of points once by this method:

1) Disconnect points at their bullet connectors (yellow / blue wires that run back by the brake switch area ).

2) Connect a test light to battery (+) and the other side to either of the the points wires (the side that leads to the points, not to the coils).

3) Use the electric start or kicker to roll over the engine. If the points (or electronic ignition) are working correctly, the test light should flash on and off.

4) Repeat the same test for the other points wire (do the 2/3 if you did the 1/4 first). Both should flash on and off while the bike is turning over.

If they are flashing that means your coils are being getting "signal" to fire and the problem is likely in the coils. If the test light remains on or off and does not flash then your problem is with your points (or electronic ignition).

The same type of test could be done with a volt meter (voltage should go from 12v to 0) ... or on resistance if you tested between any frame ground and the points (resistance should go from infinite to ~0).

IW

[martin_uk]

Hi Ron

On some of the electronic ignitions they need to be fed power to the circuit board at points plate position, so there is an extra wire on top of blue and yellow going to this.

This is usually taken from the black ignition switched feed to rear brake light switch.

Sometimes float valves can be settled by a gentle tap on side of bowl with screwdriver handle.

Aftermarket valves are notoriously unreliable, best to use originals unless damaged.

Others have found it necessary to clean brass float seat area with a clean soft wood dowel suitably shaped to fit.

If carbs have sat in freezing conditions sometimes the oveflow tubes splits so fuel leaks even when level correct.

You can test by removing the bowl and filling with fuel and I use a x10 magnifier when examining carb parts.

Also check that the float bowl drain screws O rings are fitted and area is clean.

+1 on not checking spark whilst fuel/vapour is around. Best to shut off fuel if there is a leak and you want to check spark.

Sorry if not applicable to your set up or I have duplicated any points already covered

[70CB750]

Sometimes I write too much, but I suspect when explaining something someone is reading, they may not fully picture what is being written. Best to take them step-by-step when helping them through "new territory".

And, it's often likely that my explanations are already obvious to the reader, so I'm just prattling on-

My point exactly, the best teacher assumes the other person knows nothing at all and explains it in baby steps.

[calj737]

Easy, Prokop, I'm getting a man-crush on you and Nils

[mystic_1]

BTW cranking the engine over with the throttle held open can definitely cause the carbs to "overflow", because you are creating more vacuum on them with the throttle open then you would be with throttle closed. This is especially true if the choke is on. the excess gas often comes out the air box, or into the cylinders.
 
Back in my day, we used to call this "flooding the engine".

[Restoration Fan]

OK...status update and a question:

Per the PAMCO instructions:
http://www.cb750ignition.com/installation2.htm

1. Connect the red wires from both cables of the PAMCO to the black/white wire that comes from the kill switch. The black/white wire is still connected to the coil.
2. The black wire from both cables of the PAMCO is connected to the frame.

3. The green wire from one of the cables is connected to the 1 - 4 coil. (blue wire) (See #5 Above)

4. The green wire from the other cable is connected to the 2 - 3 coil (yellow wire) (See #5 above)


So:
- We have the black wires from both cables of the PAMCO connected to the green ground.
- Our green wire from the cable beside the trigger on the right of the PAMCO is connected to the blue wire from the 1/4 coil.
- Our green wire from the cable beside the trigger on the left side of the PAMCO is connected to the blue wire from the 2/3 coil (no yellow wire on our 2/3 coil...has another blue instead)

But here's the question:
- regarding #1 above...we have the 2 red wires tied into the same connector where the black/white wires are connected.

SOOOOOOO:

We still don't have spark on #1 and #4.  We DO have spark on #2 and #3.  We also have 12 volts at the black/white wire on the back of both coils.  And, with the switch on and the kill switch set to Run, we have 12v at the black/white connector; when you turn the run switch off, the voltage drops to 0.  So it appears that the kill switch is working.  But given all that, either we misinterpreted something in the PAMCO instructions or....we have a bad coil for 1/4? Any other ideas?