Topic: 75 CB wont turn over!!

[Legion0127]

Hey guys! Ive been creeping on this forum for awhile and finally decided to sign up. Hoping you guys can help me out, im stumped by something. Im finishing up a 75 CB750 scrambler build for a customer. New Dyna Ignition, new coils, wires, and plugs. New 40/135 jetting in the carbs, tank liner,  K&N pods, Carpys 4-1 exhaust. New controls, levers, lights, rectifier/regulator combo. Compression is spot on across the board. Spark is awesome, all plugs are wet. This heffer wont start for the life of me. The only thing I can think of is that its a wiring issue. The only wiring issue I can see is the wiring harness the customer gave me was OEM, and obv everything else is new. In the back end there was a plug that went unused  with a yellow/red, green/red/, green, black, and light green/red pluged into it. The only thing coming out the other side was someone had rigged up a jumper for the green/red to go to the solenoid. No other wires going in were jumped to anything, everything else is plugged in, according to the manual wiring diagram that plug doesnt exist, and nothing ive found online is helping me.  Any ideas?

[DustyRags]

So you've got compression, fuel, spark. How's your air? How's your timing?

[cakey]

You said it had new dyna ignition. On my gl1000 the dyna s comes with a really weak plastic splice connector to run the 12v to the dyna. If it comes loose there is no power to the ignition (really easy to happen). The red wire from the dyna got spliced into the indicator on mine.

On the cb750 I think the splice connector with the red wire runs to the black and white wire to the coils to get its power. Might want to double check it that it hasn't been knocked loose whilst working on the bike. I would also recommend to solder that wire so it doesn't come loose while your riding.

Just worth checking I reckon.

[Black 750K8]

Hey guys! Ive been creeping on this forum for awhile and finally decided to sign up. Hoping you guys can help me out, im stumped by something. Im finishing up a 75 CB750 scrambler build for a customer. New Dyna Ignition, new coils, wires, and plugs. New 40/135 jetting in the carbs, tank liner,  K&N pods, Carpys 4-1 exhaust. New controls, levers, lights, rectifier/regulator combo. Compression is spot on across the board. Spark is awesome, all plugs are wet. This heffer wont start for the life of me. The only thing I can think of is that its a wiring issue. The only wiring issue I can see is the wiring harness the customer gave me was OEM, and obv everything else is new. In the back end there was a plug that went unused  with a yellow/red, green/red/, green, black, and light green/red pluged into it. The only thing coming out the other side was someone had rigged up a jumper for the green/red to go to the solenoid. No other wires going in were jumped to anything, everything else is plugged in, according to the manual wiring diagram that plug doesnt exist, and nothing ive found online is helping me.  Any ideas?

First in the title you say it won't turn over that means it will not rotate or spin. Then you say it won't start that means it will turn over but not run or fire up. Two different things. Do you have both problems?

[Don R]

My experience has shown it you have good fuel, good spark and compression there must be a problem with the timing of the 3 events. Dry the cylinders, if they are loaded with gas new plugs will just refoul. Blow some air in or just let it sit with the plugs out.
 I think the striped wires are usually switched ones, a picture is worth a thousand words.

 And won't turn over usually means it won't crank at all. I assume since the plugs got wet it is cranking just not starting.

[Don R]

K1 wiring diagram,similar to your K4/5, the striped wires go to oil, neutral, brake etc, lights. Do those work currently or were they removed?
http://oldmanhonda.com/MC/wiring750K1.html.

[Black 750K8]

Don good catch I missed the wet plug part so it won't start. I don't know jack about the Dyna Ignition I saw Spark is awesome is that on all four? If not look at the Dyna. Do the K/N pods have much oil on them? Seems like air Dyna or like Don said timing.

[Legion0127]

Thanks for the response guys. I worded the title wrong, its like thissss close to starting but just cant get over the hump. The striped wires are for the indicator lights, and theyre all working. I have power at the Dyna, I tied into the switched power at the brake switch.  The directions on adjusting timing that came with the Dyna are pure junk, so theres a strong possibility I didnt adjust it right. Ive never installed a Dyna before, so im not exactly sure on how to adjust it. Im sure there is a thread for it somewhere, but im obv new here and not sure where to look to find it, but anyone have pointers on statically adjusting the timing with the Dyna? I can take pics if itll help, Im not a forum expert by any stretch so by all means tell me what you wanna see/how things work around here

[DustyRags]

The big trick to searching this forum is to use the Google custom search tool on the top left under the links, and not the search box at the top right at the very top of the page.

[Legion0127]

Thanks Dusty, I found a thread that helped me out. I was a tad off on the timing but have it spot on now. I pulled the plugs to let the cylinders dry out over night (PS Thanks for the tip, thats so simple I never thought it it. Brilliant!) so ill give it a go tomorrow and hope for the best.

I do have to say, Thank you. Ive been on other forums where the other guys posting are just plain dickheads and make you feel like a dumbass for asking any question at all. Nice to finally find a forum where everyone isnt a know it all and will genuinely help you out. Thank you, you guys rock.

[Legion0127]

Don good catch I missed the wet plug part so it won't start. I don't know jack about the Dyna Ignition I saw Spark is awesome is that on all four? If not look at the Dyna. Do the K/N pods have much oil on them? Seems like air Dyna or like Don said timing.

Yep, spark is good across the board. I oiled the pods before I put it all together. Im crossing my fingers it starts now that Ive corrected the timing. Like Don said, after thinking about it it has to be a timing issue. Ive got the suck squeeze bang blow, now to get it all in sync haha

[DustyRags]

Fingers crossed that fixed it!

Honestly, I got my first bike August of last year, and straight away got thrown into a top-end rebuild. No mechanical experience to speak of. This board made that possible, and even enjoyable. I've been wrenching ever since, and enthusiastically helping out wherever I can.

Keep us posted!

[iron_worker]

I notice you're running factory idle jet sizing with pods and a performance exhaust. I'm betting you're idle mix is way off.

Also, over oiling pods will cause excess restriction and cause it to run rich.

IW

[Xnavylfr]

Are you POSITIVE you have the point /DYNA wires hooked correctly to the coils???
The rear pickup coil on the DYNA plate goes to #1/4 coil the forward goes to 2/3 coil..
Was this engine torn apart???
AND YES!!! you can get the pickup cam 180 degrees out of time from the cam/crank timing!!!!
With the timing marks on 1/4, the small magnet on the DYNA pickup cam should be at about the 10 o'clock position.
http://www.dynaonline.com/skins/downloads/instruct/d32-1_32-2.pdf

Xnavylfr(CHUCK)