Sunbeam 250cc twin

[TTJOHN]

Can anyone offer some advice to me regarding the wiring of a Sunbeam twin scooter, I believe that I have it wired up correctly although when I try to start it after a few minutes with the ignition on, the temporary earth lead I have fitted heats up and if left runs the battery down, I do have a solid state rectifier and was wondering if this may be faulty, causing the problem, or whether I have it wired up wrong.
Any sensible suggestions heeded to, its a challenge.:-)

TTJohn

[Spaceman]

The wiring on the Sunbeam scooter is fairly standard for a BSA twin, except for the starter motor if you have one fitted. Does the temporary earth lead heat up with the ignition on but without the engine started - or does it only happen with the engine running? When you say a temporary earth lead, is this between the battery and frame and is it 1.5 mm sq cable or 2 mm sq cable? If the lead is getting hot it would be interesting to know what the current is flowing through it if this can be measured.?

[ChrisG]

First thing to rule out are the connections. Are they tight? If not a loose connection can draw significant current draining the battery quickly. I had the problem a few weeks ago on my Royal Star and the earth lead from the battery was loose and got fried.

[TTJOHN]

Just had the Avometer on the + side of the battery and it was drawing 6v 3amps when the ignition is switched on, so it seems  like I've really got a problem there, not sure it may be the solid state rectifier up the creek, I'll have to try another one tomorrow now. I am using he original harness and I've just put two new 6v coils on it.

[Spaceman]

The 6V ignition coils should each have a resistance of 1.5 - 1.8 Ohms and draw just over 3A with the contact breaker points closed which seems to be the case here - this is perfectly normal. However, if this is the current flowing through the temporary earth lead then it should not get hot.

[TTJOHN]

Thanks all for he replies on this issue, I have now sussed it, put on a new earth lead and as you say Spaceman the 6v 3amp is normal, so I did manage to get it started yesterday although the carb is not so good and could do with replacement, it has a 17mm Zenith carb which is the correct one for this bike and the size is critical, as there's not a lot of room in there for anything different (unless you  know better) any suggestions welcome.

TTJohn

[Spaceman]

As said previously, the 17 mm Zenith MX carb was also used on some Tiger Cub models which alternatively used a 17 mm AMAL 332 carb. Although you can't seem to get any new Zenith spares from Burlen, you can get some from the main Tiger Cub spares provider:

https://triumphtigercubspares.co.uk/product-category/zenith-carburettor/