Phil Read Rep - 15 Amp Main Fuse keeps blowing

[Viper]

Hi Folks,

I have just finished putting the big PRR back together. Took it for a spin after getting it MOT'd only to find it keeps blowing the 15 Amp Main Fuse. The net result is no lights, no starter, nothing. The first time it blew was travelling along the road at 70 mph then nothing. I replaced the fuse only to find it blew the second time travelling at 30 mph. The third time it blew was after a short run out. I switched the bike off, had a chat to a friend turned it on tried the starter but the dam fuse had blown again.

Any ideas? I read on the forum that the ignition with may be at fault?

[Lobo]

A real pain .. could be anything.

Feel free to use a house mains 13A fuse whilst you trouble shoot, easier / cheaper to source.
I'd suggest bouncing / wiggling the loom / turning the headstock everything in an effort to promote blowing a fuse - ensuring that the circuits are all live, eg indicators, lights on etc. If this is 'successful' you've at least narrowest to a problem area.

Wrt the suspected ignition circuit, you could try 'hot wiring' it direct from the battery +, ie take a length of (at least) 5A wire (with an in-line fuse if poss) and connect it between the battery and thence as 'upstream' of the coils as you can get, ie within the headlight(? PPR) directly to the black input to the IGN kill switch, or failing this the black / white that comes from it. (if the latter beware the IGN will be on 24/7 and so you may damage coils if left powered too long - the in-line fuse would help here ie used as a switch. Furthermore, in a spill the kill switch would not work)
Moving on... the ignition circuit would now be completely isolated from the rest of the bike circuitry, and one way or another could be ruled out.

Simon

[AshimotoK0]

Only use mains 13A fuses as a temporary fix. DC fuse ratings are totally different characteristics to AC mains fuses. Better than a nail though 

[Waggles]

Had this on my F1, although it only blew the fuse about once a week.

I have still got all the original electrics / fusebox etc. I cured it by cleaning all the ignition switch connectors and sprayed switch cleaner into the switch and also cleaned up all the connectors on the back of the fuse box as well as the actual fuse connectors.

Which was the problem? I think it was the fusebox as there was evidence of overheating and discolouring around the main fuse.

Been OK for well over a year now so I count it as fixed! 

[Spitfire]

I had a main fuse problem on my F1 and it also turned out to be the fuse box, it looked great from the front but it was pretty badly corroded on the back.

Cheers

Dennis

[Lobo]

.... forgive me Ash, I honestly thought in a such a low volt circuit (ie 12v DC) it'd be fine. Appreciate higher DC volt circs may have genuine (fuse) arcing issues.

Regardless, agreed never a long term solution!
S

[haynes66]

and once youve sorted it, lots of pictures please!!

[Viper]

Thanks for all the advice lads. I'll get started and keep you all posted with the developments. I'll get a few pictures up once I get the fuse issue sorted.