Bike wont start and then gives a backfire

Hi, hope someone can help. Bike wont start. It throws over, but won't catch. It then gives a huge backfire. Any suggestions? (Battery is fully charged, and plugs are ok)

Thanks

 

Has it been running?
Get the plugs out, ground them on the head & check for a strong spark.
Then check fuel flow, starting at the petrol tap, in-line filter, if fuel is flowing then it's clean the carbs time.

 

Hi, thanks for the reply - yes, bike has been running fine. Petrol is flowing as I drained all the petrol and replaced it and all 4 spark plugs have been pulled out to check for spark, which they all do. Regards, Geraint.

 

you may have put the plug wires on wrong, I know it sounds silly and none of us want to admit it, but it happens, one coil goes to 1&4 which are the cylinders at the far ends of the motor, and the other coil goes to 2&3, in the middle. I forgot which coils go to which though. hopefully another member will tell you if you don't already have a manual.

it maybe didn't start for a different reason, and when you checked the plugs the wires may have gotten mixed up

 

If it had been cutting out then I'd point at your TCI. Mine would run then just cut right out. Pull over then crank, crank, crank, turn key 'off' -- boom, backfire. The TCI was full of cold solder joints and after re-soldering it's run like a top...

If you care to go down that road any decent electronics shop would be able to refresh the ignitor with new solder and stuff, if that's indeed what it is. OLD TECH.

 

Thanks everyone - checked leads - all ok. Suspicious of the igniter as mentioned by "mwhite74". Just ordered one, will keep updated. Thanks very much

 

I too would be pointing to the ignitor. One of the other techs here had the same problem with another bike and traced it to the ignitor. So if all else is off the table it is a symptom of a fulty ignitor.

Cheers
Dave

 

Could be a weakish battery, when cranking, there isn't enough juice to spark, but when you let off the starter, the TCI will "shut off" after a few seconds and spark.

THIS spark WILL go because you're not cranking the engine at the time, so even a weak battery will fire.

Could be this, or it could be bad solder, you'll find out when you get your new one

 

Don't chuck out your old unit either when you get the replacement, get the old repaired or re-soldered then you have a spare ;D

 

Wasn't there someone on here that rebuilt/soldered TCI's that I read about? Rick, was it you? Can't remember. I have a spare and wouldn't mind getting this done to it.