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Discussion Starter #1
OK.
1. New bike to me, (1975 CB400) but there are only a few wires here, and all are in good condition. (Don't ask me to check all connections under tape . . I already did. Soldered and solid. Like new.)
2. Battery. New
3. Gas. New
4. Ignition-Dynas
5. Plug wires numbered 1-4, one is on the left, 4 on the right. Plugs 1 and 4 are on one coil, plugs 2-3 are on another
6. Ran when parked.

Symptoms. When trying to start (Rollers), just gas comes out of the exhaust, no firing. But when I turn the on off switch to off, she fires (a backfire actually, as the engine is NOT turning at that time, it is just sending a signal to the wire/wires) (It is a simple small switch, and works, I checked it, Don't ask me that) So the coils are working, the plugs are working, but it is not getting a signal to fire.

Question 1. Am I missing something ?
2. Is the sending unit on the crank supposed to be a metal cylinder that is bolted to the crank but 1/2 of it is turned away (hard to describe this, but if you've seen a dyna, you'll know what I am talking about)
3. So I am either getting signals to the plugs and the timing is WAY off, (180?) or there is no signal getting to the plugs and something else is happening.
But the thing is, even IF the timing was way off, I would think I'd get some backfiring or something. but there is NOTHING. no sounds.

There are no other wires on this bike. two wires from battery, one to ground, one to coils. Tach is wired with three wires. There is NO FUSE, so don't ask me that.

There are no grounded wires, everything is solid. I guess I am curious about what the firing order is, and whether the plug wires are on correct position.

Any brilliant ideas? GEETO?
scott



Edited by - imslow on Nov 30 2007 12:07:26 PM

Edited by - imslow on Nov 30 2007 12:07:44 PM

Edited by - imslow on Nov 30 2007 12:08:16 PM
 

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Discussion Starter #2

this is the ignition on the crank. As noted by JB below, there is not supposed to be more than .040 . . . . clearance . . . is the unit missing off of the crank? It looks like it to me. . . There is probably .175 to .2 clearance between the thingy on the crank and the PU units.

I have not been able to check if there is spark while the bike is cranking as I am by myself . . . I can do it this weekend when someone comes by to help.



Edited by - imslow on Nov 30 2007 12:42:24 PM

Edited by - imslow on Nov 30 2007 12:48:19 PM
 

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Evil,
It's firing when you turn the switch off because when the power is shut down to the coils they discharge...which you probably know.

Sounds to me like the trigger isn't working. I know you have a new battery....check the voltage when it's charged, Dyna's a very sensitive to supply voltage. Also, older dyna's can be damaged if the ignition is left on for a time while the bike is not running...it can burn out the amplifier box. Not sure how to test that short of replacing the unit.
The clearance between the trigger rotor (magnet wheel) and trigger stator is supposed to be something like a max of .040"

Knowing George the bike was probably running great, was turned off, drained of fluids and parked. Yes I'd check the wiring from the trigger to the amps again. Personally I've never seen a Dyna die from being left on while the bike was not running...but I know the instructions for the older units said not to do it. It's not like 30 seconds would hurt it, but five or ten minutes might. I think if the trigger is in the right location it will feed juice to the amps and overheat them if it's left turned on. The newer versions have something to prevent that I think.
JohnnyB
 

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Evil
I fried 2 Dyna's on the sidecar when I first got it due to voltage drops, both times burning out a trigger. 1st one was new, 2nd one was the one taken from my R75 race bike that ran total loss for 3 seasons so I know that was a proper funtioning unit when I mounted it up. The battery voltage was not down but the drain of the fuel pump and brief engaging of the starter motor was enough I guess. Went back to points and all was fine.
I'm not slagging on Dyna's at all but just to say the switch left on theory could do it there is no way to check other than insalling a new one.
 

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Discussion Starter #5
Thanks, Bill, but does it look as though the magnet unit is missing off the end of the crank? Or is that it? It doesn;t look like it to me.
 

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It looks different than the one for the BMW, which is all black with a small magnet epoxied in. I don't know if anything is missing on this one in the photo.
 

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Evil
I think this is the same unit the 350 twin guys use??? Maybe somebody who has used this recognizes it???
 

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Discussion Starter #8
Problem solved!! The unit IS missing off the end of the crank. GdC is sending another one to me . . .

Thanks. I knew it was pretty obvious.
 

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is the unit fully retarded? or fully advanced? glad you found your problem, but i know that my dyna wouldn't run the bike unless i ran it fully advanced. you may try dicking around with ign timing when you get it all running.
just a thought.

'72 cb750
'75 cb750
'76 cb750
 

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Can't wait to get outta this sling and get my mojo back. I'm commin back next season, ready to shred!!!!


matt

latered
 
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