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Discussion Starter · #1 ·
Let me start by saying I don't mean to beat a dead horse with this thread, but I've had no luck searching and thought submitting my thread would cut to the chase. So I just bought a non-running cb450. Previous owner said it was previously "running" and he had rebuilt the carbs recently, just had been sitting with a drained tank for sometime and had no battery.

I'm trying to fire her up, I can hear the engine turning, but won't run. I swapped new plugs in, however, no luck. I tested the end of the spark wire with a multimeter and it seemed to get some current, however when I tried ground a plug to the frame, I saw no spark. I want to trace/test the electrical system to see where the problem lies and was hoping someone could steer me in the right direction as to which components to test in order to isolate the issue.
 

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Sensei
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Check for 12V at the "two-plug" connector (black with white stripe wires that go to the coils)... IF no voltage, check "kill" switch (this is a common problem)


IF you have 12V (read across to a ground at the black/white coil wires, and at the points, the bike should try to run (assuming compression and fuel/air mix)

To eliminate all possible wiring issues, Jump B+ to both black/white coil wires and ground B- to the frame.... If you don't have a spark it's bad coils or bad points
 

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Discussion Starter · #3 ·
66Sprint said:
Check for 12V at the "two-plug" connector (black with white stripe wires that go to the coils)... IF no voltage, check "kill" switch (this is a common problem)


IF you have 12V (read across to a ground at the black/white coil wires, and at the points, the bike should try to run (assuming compression and fuel/air mix)

To eliminate all possible wiring issues, Jump B+ to both black/white coil wires and ground B- to the frame.... If you don't have a spark it's bad coils or bad points
Thanks so much! I had signal at the 12V at the "two-plug" connector (black with white stripe wires that go to the coils). Sorry if this is an amateur question but which wires are B+ and B- ?
 

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B+ is battery positive terminal.....
B- is battery negative terminal.....
 

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Discussion Starter · #5 ·
So is it right to assume that since both coils had 12v signal, that means my coils are bad?
 

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NO!...Think of the black with white stripe wire as incoming power....A 12V reading just says you have power to there....

In order to energize the coil, it must complete the circuit through the OTHER coil wire to a ground, ( which is provided by the closed points).... When the points open, the collapsing "induced charge" in the coil is diverted to/through the next available ground (the spark plug).... If you do have 12V at the black/whites, open the points manually and insert a slip of paper/toothpick, etc. to remove the ground... You should then read 12V at the points terminal bolt (the points end of the yellow and/or blue wires)...... If you get the 12V readings, the primary coil windings are conducting and theoretically OK.......BTW, if the power is on, the spark plugs should fire as you open the closed points.....
IF all that works, you have most of one of the three requirements for the engine running... (to be complete, that spark has to occur at the correct time.....)
The other two requirements are compression, and a fuel/air mixture to burn in the cylinders......
 

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Discussion Starter · #7 ·
Well, disconnected from ground per instruction, and yes, 12v was had by connecting the yellow/blue to the black/white wires. While coils were disconnected from ground, I'm still not getting spark at the plug. Perhaps bad plug wires? Is there a way to test? Whats the next step? Thanks again in advance!
 

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The coil and hence the plug ONLY spark JUST as the points open... (break the ground)... You now obviously have power all the way to the points, so manually pulling/opening should be causing sparks at the plugs (IF the plugs are good)...IF not, unscrew the plug "boot' from the plug cap and insert a sewing needle/small finishing nail.... See if a spark jumps across that to ground as you open the point for that coil (hold/tape it fairly close but not actually touching a ground)
 

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Discussion Starter · #9 ·
66Sprint said:
The coil and hence the plug ONLY spark JUST as the points open... (break the ground)... You now obviously have power all the way to the points, so manually pulling/opening should be causing sparks at the plugs (IF the plugs are good)...IF not, unscrew the plug "boot' from the plug cap and insert a sewing needle/small finishing nail.... See if a spark jumps across that to ground as you open the point for that coil (hold/tape it fairly close but not actually touching a ground)

Tried grounding a plug, then breaking the ground: Nothing
Tried the finishing nail in the wire trick while breaking the ground: Nothing

Could my wires be trashed?
 

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Do you have any spare wires that are know to be good? Take one of something else and recheck for spark. Do you visually see you points opening and closing?
 

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scatman200 said:
Tried grounding a plug, then breaking the ground: Nothing
Tried the finishing nail in the wire trick while breaking the ground: Nothing

Could my wires be trashed?
You obviously misunderstood the concept... The coil secondary (which is attached to the plug) gets an impulse of power ONLY just as the primary coil winding loses its ground through the points (as the points break)...
It NEVER works just by grounding then ungrounding the plug wire!... Hold the plug wire/nail CLOSE to a ground and manually break the points....A spark from "nail" to ground means the coil is good, no spark means it is bad....
IF the coil is good, either the plug cap (common) or the plug is bad......
 

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Discussion Starter · #12 ·
66Sprint said:
scatman200 said:
Tried grounding a plug, then breaking the ground: Nothing
Tried the finishing nail in the wire trick while breaking the ground: Nothing

Could my wires be trashed?
You obviously misunderstood the concept... The coil secondary (which is attached to the plug) gets an impulse of power ONLY just as the primary coil winding loses its ground through the points (as the points break)...
It NEVER works just by grounding then ungrounding the plug wire!... Hold the plug wire/nail CLOSE to a ground and manually break the points....A spark from "nail" to ground means the coil is good, no spark means it is bad....
IF the coil is good, either the plug cap (common) or the plug is bad......
Each coil has black wire with a ring terminal (ground wire correct?) which I manually connected and disconnected in an attempt to generate a spark. I used this method with a spark plug (brand new, bought yesterday) and a second try with a finishing nail. Hit the start button and no spark either, however coils did get warm after this test.
 

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Discussion Starter · #13 ·
1971 CB450 said:
Do you have any spare wires that are know to be good? Take one of something else and recheck for spark. Do you visually see you points opening and closing?

I have a fully functional 82 cb750sc (DOHC) in my garage, I don't suppose I can use its coils to troubleshoot can I?
 

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.....Each coil has black wire with a ring terminal (ground wire correct?) ...(NO, Not necessarily, and I assume from this they aren't the stock coils..... Regardless, the coil positive terminal or wire must run to the Honda Black/white wire, the Negative terminal must run to the point, NOT any other ground....)....which I manually connected and disconnected in an attempt to generate a spark. I used this method with a spark plug (brand new, bought yesterday) and a second try with a finishing nail. Hit the start button and no spark either, however coils did get warm after this test...Coils getting warm means they are getting power (which we already knew)....
Do you have any "alligator leads" (jumper wires with alligator clips on both ends?)...I'll explain a coil test that eliminates all other possible problem areas...
 

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Discussion Starter · #15 ·
66Sprint said:
Do you have any "alligator leads" (jumper wires with alligator clips on both ends?)...I'll explain a coil test that eliminates all other possible problem areas...
No , but i don't mind making a trip to radioshack...

Again, I appreciate the help/guidance so much,
 

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At least three..... Here it is...Quick and dirty.....

 

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Discussion Starter · #18 ·
Followed your diagram. Everytime I touch the coil (-) to the battery (-), I got sparks off the alligator lead clip, but nothing at the plug. Is this a good or bad sign?
 

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So far test is working...the coil primary is good.... that spark at the battery - when you "touch and remove" is normal....Plug should/can spark only when/as you remove...BUT it didn't...
That means : either the coil secondary is bad, or the cap or plug is bad......
Remove (unscrew) cap from coil wire and stick the nail back in.....
position (tape it down, don't hold it, you may get shocked) nail NEAR (1/16") but not touching the alligator that was on the plug threads (all other wires/connections as before)
repeat the touch and remove clip action while watching that 1/16" gap at the nail...
A spark at the nail gap will indicate coil secondary is good (entire coil is good) and its either the cap (as I suspect) or the plug..... New caps are available and just screw back in.....
NOTE THAT the battery positive is/MUST BE connected to the coil positive (black/white wire on Honda coils)
 

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Discussion Starter · #20 ·
Upon connecting the coil (+) to the battery (+) all of my light go on, this is correct right?

Still no spark with the nail taped 1/16" from the clip :(
 
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