[Mike gb]

Hi all,
I have a TW125 in North Yorkshire UK. After sorting out the wiring, everything now works as it should with one exception.
It bump starts easily but won't fire up using the electric start. It churns over but doesn't fire.
To get it this far (it was dead when purchased and only the back light worked) I have replaced most of the wiring and the CDI unit, battery, HT coil, lead & suppressor cap. Filled the hole in the petrol tank and renewed the split fuel hose. Cleaned out the carb and jets.
Any thoughts on how I get it running using the electric start please?

 

[robtattoo]

Could be that the battery doesn't have the gumption to spin it quickly enough AND provide a spark. That's be my first guess.
Check for a good blue/white spark when you're cranking it over, first.

If you don't have any joy, Will Bratley at WEAB motors in Malton, or Gary at Genspeed in York will fix you up.

 

[Ski Pro 3]

I agree with rob. The battery, while cranking, is probably drawing down below 11 volts and that won't fire the CDI to create a spark. A tell-tale sign is when releasing the button just at the right time will sometimes cause the motor to catch. At that moment, the starter isn't draining the battery and the motor momentum is enough for one more revolution to the fire stroke. You might try a jump start on the battery with a big strong battery to prove the point before springing for a replacement. Maybe just connect a digital volt meter to the battery and measure the voltage during the cranking to see what it drops to.
Cheers!

 

[Mike gb]

Thanks guys for the pointers, much appreciated. I will try the releasing the button and see if that works. The battery is 7ah which is bigger than recommended and brand new so it would be a bit disappointing if I jump start it off a car battery or a charger but no worries if it cures it. Just a thought, will it melt anything jumping the battery off a bigger one?

 

[robtattoo]

Nope.
I wouldn't do it every day, but I've jumped off hundreds of bikes with no problem.
Did you buy a regular lead-acid battery? It seems like about 1 in 5 comes with a duff cell these days. When i bought my bike, i switched out the original battery for an AGM. Still 7AH, but with much higher cold cranking amps. It spins over much quicker & fires up right away. It was hit-&-miss with the original.

 

[robtattoo]

The stock Yuasa spec battery only has 105ish cranking amps, which'll barely pull the skin off cold custard.
You can buy AGMs the same dimensions with upwards of 150 CCA. Usually for less money too.

Zipp Battery YTZ7S Maintenance Free Replacement Battery for ATV, Scooter, Dirt Bike, and Motorcycle: 12 Volts, 6 Amps, Nut and Bolt (T3) Terminal https://a.co/d/8pFg1S6

 

[Mike gb]

Cool, thanks robtattoo and everyone else. If it works off a car battery then the AGM battery is the answer. Will see if they sell them over here. Thanks again to everyone. It will most likely be Friday or Saturday before I mess around with it again but will post the outcome on here for information. Another tw brought back to life, which is good!! Just a paint job to do on the replacement tank when the weather gets warmer 😎👍

 

[Ski Pro 3]

Something I've discovered about lead/acid batteries is that a simple charger rarely brings them to 100% full charge. In order to REALLY get a battery to full charge, I've used a 20 volt, 1amp charger. This is commonly referred to as equalize charging a battery. A power wart I got off an old laptop that output 20 volt, 1amp is what I use. It's the current you want, not the voltage. So it will put 1amp constant current into the battery. Monitor the voltage. At first, you'll read maybe 12.7 to 12.9 volts at 1amp. Keep the charger on and when the volts reaches 15.5volts and the amps drop to a few tenths, then remove the charger. On some batteries, it takes me weeks to get them revived and equalized this way. Keep an eye on the water level and top off daily. Soon you'll notice current doesn't drop any further and you are still boiling off water. That's when you know you maxxed out the battery charge.

Give it a try, what do you have to lose? Do not do this on lithium or any sealed battery, only lead/acid where the caps are removable, and you can add water. Make sure it's distilled water too.
I've got a rather large bank of RV batteries people gave me, claiming they were bad, that I've restored using this method of 1amp/20volt charger and letting it equalize for a week or two. I use them for my barn, along with solar panels and an inverter for providing AC power to the barn.

 

[002WT]

Get a lithium battery and be done with it.

 

[Mike gb]

Thanks for all the advice guys. I have a few things to try before investing in a lithium battery.😃

 

[Fred]

Good plan Mike, and good luck.
Don't let us spend all your money before you can further diagnose your issue to your satisfaction.
Often just a poor connection has us unnecessarily replace circuit elements. Simple tests can be measuring resistance between battery ground post to cable and from post to frame and motor...same for resistance between battery positive post and starter relay, resistance from relay to starter motor, etc,etc,etc.

 

[Mike gb]

 

[Mike gb]

Ok, it still won't start off the electric starter button even with my car battery in parallel. Annoying, however it does still start up happily by bump starting it. The carb is now flooding so presumably the float is stuck down. Looks like that's the next job for this weekend. The patch on the hole in the tank is also leaking so I need to spray up the replacement as the weather is now above freezing. Maybe the carb issues and the non starting on the electric start are related?