GAAAAA!!! }:-[ Backfiring when starting CBR4 Gullarm

[Claud 14.7 to 1]

My bike sometimes gives off a massive BANG when starting it from cold. Once the engine is warmed up it starts 100% fine. Funny for scaring passers by, but not great for my engine/confidence in it.

The BANG happens exactly as the engine starts, it continues to run fine right after the bang. So it starts perfectly, except for the BANG sometimes, on the first revolution of the engine running by itself (ie after the starter motor). Hope you understand.

It happens rarely, but has more than usual these past few weeks. (could be weather related?)

Im not sure, but I think it might happen when either i have too much choke or not enough choke. But today for example choke was not needed, and it still backfired.

Could it be something to do with the weather? Happens more in the colder months (did happen a few time in the Summer). I cant say for sure.

Bike is kept outside, covered. But sometimes it rains on the bike, and rain could get down the exhaust pipe, also condensation could build up.

One thing which may be useful for you is the fact that I'm pretty sure my fuel tap is faulty. When it's on the off postition it still flows fuel. So basically unless I get the position exactly right (near impossible to do), the fuel is on full flow most of the time. Not sure how this would affect the bike as there is a fuel pump between the tank and the carbs.

Thanks people

[stevo123]

My old ZXR400 used to do that-knack your ears lol. Was always hard to start to unless i heated the plugs up on her. Turns out that after i sold it the head gasket had gone. Can't see that being related though. I would check the coil pick up and the connections to the cdi unit first. Mine also used to "bang" a few seconds after releasing the starter motor after a failed starting attempt. Weird machine.; Got an rs125 now-1 cylinder=1/4 worries

[MarJay]

Does it always start without choke, even on the coldest mornings?
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[Claud 14.7 to 1]

No, on the coldest mornings no choke = no start.

Even on the coldest days, with choke on, it could/would backfire sometimes. Last year proved that.

[Kram]

you might find this is carb bound, or plug bound.

Carbs... do you turn the petrol tap of when bikes not in use. as if the bike has the petrol tap on, the carbs may get flooded (especially if there is no resovoir on them, and this will cause to to much petrol going into the engine in the first turn over (resulting in the backfire). try turning the petrol off, let it go cold and try it.

Plug... corroded or old plugs?, try unpluging all the plugs(take them all out or u get many back fires), and plug one in, see if it starts, then goto next cylinder, as this will test the fuel intake.

this should define the problem, please post results. and i can tell you how to fix them


Cheers
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FS1E -> SR125 -> CB400N -> CB650 -> FZR600 Genises -> VFR400 NC21 -> CBR900RR Fireblade -> Renault Clio 1.4

[Claud 14.7 to 1]

[Claud 14.7 to 1]

Cool, mate you are in Poole, Dorset, me too!!! (Uni)

Wanna go for some ride outs? What a coincidence.

I recon it is the tap. Sounds about right. Can't fit a new one though, till I'm back in Herts: Christmas time.

[Kram]

i would go for a ride out, but i totaled my CB400 earlier in the month.. (in another post somewhere)

u got any spare bikes i could borrow;)

a carb resovoir, is basicly a small tank, with an overflow and a float in the (the same as a bog system. I THINK, not too sure though). it basicly controls how much fuel your carb can hold before it overflows.

what you could try with your dodgy petrol tap is... (i'm not sure how easy this would be on your bike)

is turn the petrol off.... and remove the tank... run the bike... till it chockes from no petrol. this will remove ALL the petrol from the carbs and resovoirs.... then let it go cold, and attach the fuel line in, leave it for about 5-10 minutes with the fuel line on. then turn the petrol off, and remove the tank again, then start the bike. if it backfires then it would Probably be the fuel tap. but it depends on if it still does it when the fuel is left on.


give feedback please...

where in poole you live. you might have heard of my crash (got on the radio (2CR;)) was on wimborne road at 8:25am on a tuesday about 3 weeks ago.


do you know anyone selling a cheap bike. gotta get back on the road (i'm getting withdraw symptoms from motorbikes
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FS1E -> SR125 -> CB400N -> CB650 -> FZR600 Genises -> VFR400 NC21 -> CBR900RR Fireblade -> Renault Clio 1.4

[Claud 14.7 to 1]

I know for a fact the tap is dodgy. It’s just a matter of assessing whether the fuel being "on" all the time will flood the bowls and cause it to backfire. Theory sounds ok.

I recon I am going to get a new tap 2nd hand, because I know for a fact mine is, for a large percentage of the time, letting the fuel past at full "pressure" whether the tap is switched to the on position or the off position. If that makes sence. hehe.

Na didnt hear about you're off, Ive only been here for abour 3 weeks myself.

I've already given you some feedback... But theres plenty more where that came from. lol.

Do you have tools? I can exchange feedback for use of tools.


No spares sorry.

[Smoto Bob]

dont think i have ever turned a fuel tap off when i park a bike never caused any problems.
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F'it DO WHAT EVER MAKES YOU HAPPY!!!!! Even if it screws over everyone else :p
Titz wrote: "..and my 3rd accident was when this police car....."

[Kram]

i've got plenty of tools, got plenty of bikes too (seen as i rebuild them for a hobby where do ya live, seen as i'm on half term at the moment, would ya be able to backfire yourself down here, n we could strip it n see if we can fix your problem?
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FS1E -> SR125 -> CB400N -> CB650 -> FZR600 Genises -> VFR400 NC21 -> CBR900RR Fireblade -> Renault Clio 1.4

[Claud 14.7 to 1]

Yeah not sure if it is the tap is causing the problem. It is faulty though.

I'll pop down, if thats ok Drummer? Sunday ok? I'll pm you my details mate.

I doubt we'll get it to backfire as it only does it every so often. We can check out the tap though. Narrow down the weak links, kinda thing...

[Kram]

only i can take your bike for a spin;)
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FS1E -> SR125 -> CB400N -> CB650 -> FZR600 Genises -> VFR400 NC21 -> CBR900RR Fireblade -> Renault Clio 1.4

[Claud 14.7 to 1]

'course

You can see how much better it is than your ex.

Na its a bitch: backfired again today. 3 times so far this week . Never use to be this much.

Now i'm, going to test it, by NOT turning the fuel tap off, see if that makes any difference. Last 2 times I turned it "off", and it backfired after I turned it on and started the bike.

So annoying.

Thing is once the engine has been on, it starts prefectly every other time. Only bangs the first time it.

[Smoto Bob]

sounds like its going to blow up to me , might as well swop it in and get a nice little green klr , which by strange bit of luck i can do you a deal on
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F'it DO WHAT EVER MAKES YOU HAPPY!!!!! Even if it screws over everyone else :p
Titz wrote: "..and my 3rd accident was when this police car....."

[Claud 14.7 to 1]

Get me a cheap old unfaired sports 750, or a GSX-R 600 Srad, and I'll think about it.

Na I think I've got more chance of blowing it up myself , but still this aint good.

[Claud 14.7 to 1]

And my lid broke this week as well. Not good.

I expected more for the price I paid for it.

[Kram]

i need a new lid, scratched mine in my crash, i'll show u my £3000 of damage to my CB400N as well;). wanna trade your bike, for 2 bikes;) i need one bad, i actually went and bouhgt apushbike today
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FS1E -> SR125 -> CB400N -> CB650 -> FZR600 Genises -> VFR400 NC21 -> CBR900RR Fireblade -> Renault Clio 1.4