More backfire on overrun.

[Neosophist]

I have a problem in which the bike backfires really badly (think shotgun going off) not your usually popping on the over-run after giving the bike some stick. It never used to do this and i've checked the mixture / carb / exhaust seals etc and theres no leaks.

I'm beginning to think the problems electrical in nature.

I've noticed that when you press the brake pedal / level, no matter what the engine speed the lights dim a bit (maybe a crappy earth)

If I rev the bike hard in a gear and back off the throttle it takes a few seconds to backfire. However if I do this and press the brake pedal / lever it starts to backfire almost instantly. I've tried this 20 times so it's not just chance that its backfiring when i press the brakes, its deffiantly happening a lot quicker / more / instantly when i press the brakes.

It's a rolling chassis + engine at the moment as i've decided to strip it completely and rebuild it.

I'm going to fit a NOS generator and an R6 reg/rec as a starting point for electrical problems.

Any other possible thoughts on what'd be causing this.

The fact it suddently started doing it one day makes me think it shouldn't be there ^_^

[G-MAN]

Sounds like electrical to me, is it like flicking the kill switch ? You could be right in having a look at the earth and maybe connector blocks etc.

[Neosophist]

Sounds like electrical to me, is it like flicking the kill switch ? You could be right in having a look at the earth and maybe connector blocks etc.

Yes it is!

I'm glad somebody else thinks i'm on the right lines here..

The voltages on the reg/rec seem 'ok-ish' but on the slightly low side. Annoyin thing is this reg-rec is 13 months old so just out of guarantee! Hence putting the R6 Reg/Rec on there.

I cleaned / GT85'd (maintaince sprayed) all the connector blocks on the bike last week while fault finding so there all nice.

I still dont like the fact that the lights dim with the brakes on even with high revs. I'm going to run a new earth from the rear-bulbs to the earth strap and see how I go from there.

Bloody electrics! :/

The plugs are also new-ish having only done 3000km. I do have a spare set I can try anyway just-incase.

[rich1988]

Not related but the other day I was in stop start traffic I let the revs drop really low it bogged down a bit then backfired like you described, literally like someone was firing a 12 gauge! scared the bejesus out of me and people in the cars around me I never realised it could be so loud!

[Cammo]

Neo: do you have the rear brake light switch attached to the rearsets? If so check if it backfires with the switch unplugged.

[Neosophist]

Neo: do you have the rear brake light switch attached to the rearsets? If so check if it backfires with the switch unplugged.

Yes I do. Do you think a faulty switch? I have one of these still in the packet somewhere...

[Cammo]

Not sure really, just something to try.

I don't think a faulty switch will cause the problem (because all any switch does really is bridge 2 contacts), but the associated wiring might be responsible if it's dodgy anywhere.