cloudy
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| posted on 5/4/08 at 08:05 PM |
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Any idea why it's backfiring so much?
I've just fitted my exhaust to my middy build, and run it up.
I'm a little worried about the amount of flame out the back... It looks great, but surely I must be overfuelling or worse?
Video: http://www.digital-car.co.uk/wr4/mk2/video/startexhausts.wmv
Ignore the high idle, hadn't got round to setting that yet. I'm also going to balance the carbs tomorrow to see if that helps.
Engine is a GSXR 1100WP
I'd like to know if people think this is fairly normal and I'm worrying about nothing - or is there a problem here?
PS. Yes I know the left driveshaft is snapped - my mock up shafts didn't take it...
[Edited on 5/4/08 by cloudy]
[Edited on 5/4/08 by cloudy]
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Dangle_kt
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| posted on 5/4/08 at 08:11 PM |
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vid wont load?
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cloudy
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| posted on 5/4/08 at 08:15 PM |
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works here, it's a Windows media player file...
James
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big_wasa
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| posted on 5/4/08 at 08:17 PM |
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Does for me. 
Wish you would put photos in your archive, it looks awsome 
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cloudy
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| posted on 5/4/08 at 08:18 PM |
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Loads of pics in my build diary:
http://www.locostbuilders.co.uk/viewthread.php?tid=54042&page=33
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mackei23b
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| posted on 5/4/08 at 08:20 PM |
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I had a look, but still a mystery.
I did some work with a westfield with a red top, it ran fine for a couple of minutes before spiting flames out the carbs and exhaust. On that occasion
it turned out to be carbon on the head falling off when hot and not enabling the valvles to seat. Once the head was cleaned it all went well.
However no idea with yours, but if no-one comes up with a deffinitive answer!
Cheers
Ian
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snapper
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| posted on 5/4/08 at 08:27 PM |
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Cam timing?
Exhaust valve opening while gasses are still burning.
Over fueling as it looks like you flame when the throttle is closed.
Probably one of those things that needs setting up with a rolling road or at least a lamda sensor
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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zilspeed
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| posted on 5/4/08 at 08:32 PM |
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It does sound a bit unbalanced in general engine note.
If the carbs are out of balance, you could be getting excess fueling.
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stevebubs
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| posted on 5/4/08 at 08:38 PM |
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excess fuel on overrun would be my guess...
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cloudy
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| posted on 5/4/08 at 08:46 PM |
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Is that due to the slides not closing fast enough?
James
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stevebubs
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| posted on 5/4/08 at 10:32 PM |
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BTW high idle isn't gonna help with the over run fuelling....
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cloudy
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| posted on 6/4/08 at 05:06 PM |
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Fixed the idle and balanced it - it's stopped backfiring but it's still hestitant to rev - Won't go past 9k on a 13k redline
3/4 plugs look perfect, but 1/2 are soaking wet and covered in carbon - far too rich. Anything in particular to check on the carbs?
James
PS. If it helps I've been having trouble with the float bowls not sealing - the fuel pump also ticks every 5 ish seconds when it's filled
the carbs, I'd assumed that was just a little bit of pressure was lost back to the tank...
[Edited on 6/4/08 by cloudy]
[Edited on 6/4/08 by cloudy]
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DIY Si
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| posted on 6/4/08 at 05:28 PM |
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When you say the float bowls haven't been sealing do you mean against the main carb body, or that the float needles haven't been shutting
off the fuel?
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cloudy
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| posted on 6/4/08 at 05:34 PM |
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I mean the needles, first time I switched on pump it ended up ejecting fuel from the air vents at the top...
James
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DIY Si
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| posted on 6/4/08 at 05:40 PM |
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That won't help, as I've been having this problem. I could switch the pump off and it would actually run better! There was fuel running
into the cylinders. Do you know if the floats are set at the right height? Have you had a go at cleaning the needles or looked at buying new
needles/seats?
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cloudy
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| posted on 6/4/08 at 05:41 PM |
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I've just taken the entire set apart and cleaned up - I think i'll run it grav fed and see if it's better...
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DIY Si
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| posted on 6/4/08 at 05:44 PM |
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That was the other thought, what pump are you using? Bike carbs are like webbers, they only like 2-3 psi from the pump.
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cloudy
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| posted on 6/4/08 at 05:52 PM |
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Using a pump from another carbed bike...
James
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DIY Si
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| posted on 6/4/08 at 05:54 PM |
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That should be ok. As you've suggested though, I'd give gravity fed a bash, as it's a free trial and worth a go. If that does work,
then your current pump is just over pressurising the carbs.
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cloudy
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| posted on 6/4/08 at 06:09 PM |
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Original bike was gravity fed, so maybe just too much for it... I presume you can get hold of adjustable regulators ?
James
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Jon Ison
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| posted on 6/4/08 at 06:19 PM |
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Have you got it to rev yet ?
Couple of things, have you got an air box on ? This will make a massive difference to how it runs, most BECS run absolutely sh**e without one ?
Are you getting air leaking into you exhaust manifold ?
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cloudy
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| posted on 6/4/08 at 06:44 PM |
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It's the same with or without a filter, and I don't believe the exhaust is leaking...
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Jon Ison
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| posted on 6/4/08 at 07:10 PM |
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std filter or after market ?
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cloudy
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| posted on 6/4/08 at 10:35 PM |
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std...
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cloudy
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| posted on 28/4/08 at 06:53 PM |
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Two problems - leaky float seals and the coil connections were making bad contact during vibration. Tries to wrap round the tacho now
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