Topic: CB750 - idles...then no spark! :-( -UPDATE! KILL SWITCH IS THE PROBLEM!

[andy750]

Ok guys this is more of a share of my frustration  ...nice and sunny day here, blue skies, fresh temps and I just got the new link for my new chain so I was all set for the first test drive of my rebuilt K2 (see pics below) - first time in 6 years!! Started up the bike (as I had done before) and set the idle high...went inside to get my helmet to take it for a quick spin around the block (depsite the front brake needing to be bled) and as I came out the bike died...ok no big deal I thought and went to start it....wouldnt fire up....starter motor ok so I thought perhaps I was out of gas (I was on reserve) - so go to gas station get more gas....come back.....still wont start.....check float bowls for fuel - ok. Check spark on #4 and #1 - nothing :-(.....new plugs as well....look under tank at wiring - all new....yep everything is there as it should be (and was before)......so Im stumped  ...have the coils just packed in!!?? I guess I can swap them with another set and check this....very frustrating  .......sometimes its just never ending.....

cheers,
Andy

[andy750]

some more....check out the new rear blinkers :-)

[750goes]

Fuse?
Ignition Switch?
Kill Switch?
Coil wires come loose?
Spark on 2 & 3 ?

[andy750]

couple more.....

[andy750]

Hey 750goes,
thanks but checked all but the spark on #2 & 3 - Ill do this....

Fuse?

Only one fuse and lights, mains work ok......

Ignition Switch?

I can hear the starter motor whirring away so I think this is ok.

Kill Switch?

Would that give me no spark? Ill check it and see.

Coil wires come loose?

checked this and seem to be ok. I guess if I switch coils I can go over this again.

Spark on 2 & 3 ?

Will check...


thanks for the suggestions,
cheers
Andy

[Ernie]

Hey 750goes,
thanks but checked all but the spark on #2 & 3 - Ill do this....

Fuse?

Only one fuse and lights, mains work ok......

Ignition Switch?

I can hear the starter motor whirring away so I think this is ok.

Kill Switch?

Would that give me no spark? Ill check it and see.

Coil wires come loose?

checked this and seem to be ok. I guess if I switch coils I can go over this again.

Spark on 2 & 3 ?

Will check...


thanks for the suggestions,
cheers
Andy

kill switch you bet

[andy750]

Whats the best way to check the kill switch?

thanks guys,
Andy

[750goes]

connect a fuse protected wire from your battery 12volts power to the black/white coil wires - before it splits into the two separate coils (hopefully there will be a connector with a double socket) then see if the bike will start with your normal procedure.

[bryanj]

OK if this was a total engine out rebuild this is what i would check in order:-
(1)  Contact wire yellow and blue wires connected at boot by rear brakelight switch

(2) Points cover off make sure advance still bolted on and points opening/closing

(3) Ground wires at coil and engine

(4) Power to points using bulb--if not chase the wiring back via
   (a) coil output (yellow and blue wires)
   (b) Coil input (black and white)
   (c) kill switch output inside headlamp shell (black and white)
   (d) specific kill switch input wire (black)
   (e) All power wires (black)
   (f) ignition switch output wire (black)
   (g) ignition switch input (red)
   (h) fuse output (red)
   (i) fuse input (red)
   (j) Battery


I would do it in that order cos thats the most common mistakes I make!!!

[andy750]

Thanks Bryan thats a great list for me to work through - I have a DYNA S installed so no points. However will check all connector leads. And thanks 750goes for the quick check method. Ok feeling better now 
Cheers
Andy

[bryanj]

Dont forget the auto advance, wouldnt be the first i seen one fall off!

[andy750]

UPDATE - 23/10/06

First of all thanks to all who replied before and I think Ive worked out that the KILL SWITCH is to blame - heres what I did:

1. Checked wires in headlight shell - 2 blacks to the connector - OK
                                                - black/white to black white - ok
2. Coil wires - all connections ok

3. With spark plug (#1) out and against engine - pressed starter button - turns over but no spark. If I then turn Kill switch on-off-on I see spark moving across spark plug/engine...but only intermittently. If I then press down on kill switch (when on postion) and press starter, I got spark across plug/engine and then it didnt work after this. Therefore I think kill switch is faulty. I looked inside the swtich and couldnt see a whole lot although a black wire had some copper wire showing where it connected.

So my question is: is it easy to dismantle the housing to look inside and fix the kill switch? (buying a new or getting a spare control is not an option here as I have matchig polished controls on this cafe rebuild - see pics above -and I like the look :-).

Or alternatively can I temporarily bypass the kill switch to see if I can get the bike running? Im not very electrical minded so dont be afraid to tell me step-by-step what I should be looking for or do. Bryans post was spot and I followed this tonight to isolate the problem (or so I think I have!).

thanks for all the help/suggestions so far and I feel less frustrated now knowing the problem!
cheers
Andy

[750goes]

The off/on/off switch can be a bit fiddly when dismantling, as it has a VERY SMALL ball bearing and EXTREMELY SMALL SPRING that is held in by a screw inside the housing, this is after you remove the wiring.

If I had to do one again I would recommend a white sheet all around you so you can find all the pieces easily...

The switch itself could be pretty dry and not getting a good contact... spray some "inox" into the kill switch top and underneath and move it till it gets nice and free - then try it again before complete disassembly, it may now work as these surfaces can get pretty gummed up over time... The INOX spray will also assist in dissolving and penetrating any corrosion present - even if you can't see it..

let us know what the plans are - it may be cheaper to buy another working part...