Topic: Can't get my '77 CB750 started

[Bertie]

Hi guys,

I'm new to this forum and to the CB750!  I'm looking for advice on my bike as I can't get it started.  I realise I'm one of those annoying newbies who's just bought a motorbike, without knowing enough about them to keep it going, but I'm enjoying it alot, and some help would be greatly appreciated.

So the last time it was riding everything was fine until the throttle cable snapped.  I replaced both of them with new cables and they're working as they should be.  But I can't get it started now.

The battery is new and charged up,  I'm using the electric start with the choke on, but it won't start up.  I pulled out the plugs and they were very wet, so I wiped them dry and put them back in, but still no luck.  There is a blue spark coming from the plugs, and there is compression.  The plugs are new as well.

There is plenty of petrol, and the kill switch isn't on.  I'm presuming I've tried to start it on the choke too many times, and that's caused the problem. 

I've probably made a school boy error somewhere, but I'm loosing patience on my own and need some help.

Thanks for taking the time to have a look!

Bertie

[Black 750K8]

Maybe you have flooded it try again don't give it any gas and leave the choke open spin it for about 15 seconds and see if it tries to hit. If you pull the choke all the way up that will give it more gas and flood it even more. Or pull the plugs and blow them dry

[Vinhead1957]

Try new plugs I have flooded plugs and a new set made it fire in an instant.

[martin99]

How long was it laid up waiting to be fixed? If too long you will get water separation in the crap that passes for petrol these days. Make sure you are using fresh fuel.

[tlbranth]

Bertie - I'm betting that when you replaced the cables you disturbed the ignition somehow - like around the coils. Check for spark by pulling a plug, connecting it to the plug cap, grounding the plug and cranking the engine. Also make sure your kill switch isn't on - since replacing cables necessitated messing in that area.
It definitely sounds like no spark.

[Black 750K8]

Bertie - I'm betting that when you replaced the cables you disturbed the ignition somehow - like around the coils. Check for spark by pulling a plug, connecting it to the plug cap, grounding the plug and cranking the engine. Also make sure your kill switch isn't on - since replacing cables necessitated messing in that area.
It definitely sounds like no spark.

He said he had spark and the kill switch is not on.

[Bertie]

It's been sat for about 4 days before I fixed it. 

Thanks for the replies, Black 750K8  I'll give that a go later on.

It's also pretty cold over here in the uk which probably doesn't help her!

[martin99]

Just a thought - is the choke opening when you push the knob down? Sometimes the mechanism can get stuck in the closed position. (common problem with pods)

[70CB750]

You have to keep the throttle half open to start, dont ask me how I know

[tlbranth]

Bertie - I'm betting that when you replaced the cables you disturbed the ignition somehow - like around the coils. Check for spark by pulling a plug, connecting it to the plug cap, grounding the plug and cranking the engine. Also make sure your kill switch isn't on - since replacing cables necessitated messing in that area.
It definitely sounds like no spark.

He said he had spark and the kill switch is not on.

Oops. Sorry. Better read more carefully.

[Bertie]

Just a thought - is the choke opening when you push the knob down? Sometimes the mechanism can get stuck in the closed position. (common problem with pods)

I'll have a look tomorrow night, but I haven't got pods.  Everything I've read about them sounds a bit beyond my skill set!

If the problem is to do with flooding, will I need to do anything to the carbs?  Just a mate said something about draining the carbs if I've used the choke too much.

[martin99]

There is an upright overflow tube in the float bowl so theoretically this should prevent them from being too full, the fuel would just drain out of the rubber tubes attached to the underside of the bowl. If you want to drain them you can, by turning out the brass screw on the underside of each bowl - just have a container under the rubber tubes to catch the fuel.

[Don R]

I'd try fresh plugs, let the cylinders dry out before installing them. Draining the bowls can't hurt.

[Stev-o]

Just a thought - is the choke opening when you push the knob down?

Knob down? If it's stock, the '77 has a cable operated choke that he would pull up.  And with PD carbs, I give the throttle two twists then hit the start button.

[Black 750K8]

Berti
 When I was talking about flooding I meant the combustion chamber. If that were the case it would clear its self up after sitting left alone for about 30 minutes. When you try it next time do what Stev-o said two big twist this should squirt raw gas then pull the choke all the way up do not give it any more gas hit the starter. If that does not work we need to start trouble shooting AIR FUEL GAS all at the right time got to be one.

[martin99]

Just a thought - is the choke opening when you push the knob down?

Knob down? If it's stock, the '77 has a cable operated choke that he would pull up.  And with PD carbs, I give the throttle two twists then hit the start button.

That's what I meant. With the knob down, the butterflies are open. When it's pulled up, they close. I was just suggesting they may be stuck in the closed position, if the mechanism is hanging up on anything.

[Stev-o]

Just a thought - is the choke opening when you push the knob down?

Knob down? If it's stock, the '77 has a cable operated choke that he would pull up.  And with PD carbs, I give the throttle two twists then hit the start button.

That's what I meant. With the knob down, the butterflies are open. When it's pulled up, they close. I was just suggesting they may be stuck in the closed position, if the mechanism is hanging up on anything.

Got it, "choke talk" can be confusing.  Closed is on, down is off, open is off, up is on!

[Carver]

Just a thought - is the choke opening when you push the knob down?

Knob down? If it's stock, the '77 has a cable operated choke that he would pull up.  And with PD carbs, I give the throttle two twists then hit the start button.

That's what I meant. With the knob down, the butterflies are open. When it's pulled up, they close. I was just suggesting they may be stuck in the closed position, if the mechanism is hanging up on anything.

Got it, "choke talk" can be confusing.  Closed is on, down is off, open is off, up is on!

Yeah, thats why I fouled a bunch of plugs on my 450, everyone refers to chokes differently and I kept mine engaged and kept bogging and fouling plugs until I figured it out.

Are you giving it any throttle on start up? Mine wont even start without the throttle cracked



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[CBcafeJunkie]

Same issue seems my bike was running to rich. Spark plugs out all wet, tried cleaning them, no avail. Gonna try new and heat gun on old

[CBcafeJunkie]

Got mine up and running seemsi had fouled my iridium plugs got some standard nkg's and vroom!!!! Took a few tries and easy on the gas with the choke up

[martin99]

Glad you got it sorted CB. It would have been nice to hear how the OP got on with his problem too, might help others reading these forums to pin down issues on their own bikes.

Unfortunately there's a lot of it about...