Yamaha 250 Moto4 starting problem

[Hair Bear Bunch]

Hi, I'm hoping there's a simple answer to this if anyone can help...
I'm working on a mid '80s 250 Moto4.
The starter winds it over ok but it won't start.
One pull on the cord and it starts first time every time - with or without the battery connected.
I have tried running a lead direct from the battery to the starter, it spins over but still won't start.
The leads to the battery have been replaced, as has the solenoid, and the lead from the solenoid to the starter, it's currently running off a 65ah car battery.
I'm sure I've read about this problem somewhere before but I can't find it.
Any input would be greatly appreciated.
Thanks,
Rob.

[nd4speed]

Does it have spark?
Is it getting fuel?

You try to spray ether(starting fluid) in through air box while starting? Or put couple drops of gas in cylinder?

[Hair Bear Bunch]

Spark - Yes
Fuel - Yes
Gas in cylinder - Yes
Didn't try ether as the engine was already hot.
I just don't understand why an engine that starts instantly on a cord will not go on the electric.
What is there in the starter circuit/system that could cause the spark to breakdown under compression when the electric start is used?

[nd4speed]

oh I missed the part where it starts with pull cord. Hmm...the stator is good. perhaps the starter is not rotating motor as fast as pull cord?

[Racer-X]

Maybe a safety feature? Im not sure if they would have had something like that back then but I have a polaris that has electric and kick start. It will kick start anytime, but will only start with the starter if the brakes are being depressed. It has a sensor . Or maybe the old battery just doesn't have enough power any more?

[oscarmayer]

did you hold the brake lever in when starting? some models had a brake lever safety or clutch safety.

[Hair Bear Bunch]

Hi,
It's hooked up to a well charged car battery so power loss / crank speed shouldn't be an issue.
Hadn't considered the clutch/brake lever - food for thought...
Thanks for the ideas, will report progress (if any!).

[oscarmayer]

if you used a car battery you may have fried the electronics, some electrical systems do not like being hooked up to a car batteries as the amps are too high and can fry the cdi or volt regulator, thus damaging other stuff.

[Hair Bear Bunch]

The latest instalment...
Can't find a brake lever switch so ruling that out for now.
Turning over by pull cord or starter gives a good spark. But, noticed today when using the starter if you give even the slightest bit of throttle it all but stops the engine cranking. Does this suggest a timing issue?

[Hair Bear Bunch]

Aha! found a switch in the left brake lever mount - tried it both ways, didn't make any difference, rats!
So lets go at it another way, started it on the cord and gave it a good run around the fields for about half an hour to get it good and hot. Swiched it off and went straight for a restart. Still no show on the electric but first time on the cord!
I really didn't want to start taking the plastics off this thing because it's a real pain but I think now it's nothing more than a silly earthing fault somehow somewhere so I don't see many options.
Workshop manual on order and patience on standby, will let you know.