Bogging down at higher RPM and backfiring

treeno · Crazy Courier Joined: 26 Dec 2012 Karma :

First post in here with the new (old) GPZ500. Laughing

Went for a quick blast with a pillion the other day, all of a sudden when we are nearly back home I notice that giving it more throttle is not doing anything, it was perfect before. Anyway now whenever I try and accelerate past around 6k I just have no power and it bogs. It will slowly pick up speed but nothing like it should. If I hold the throttle on it will sometimes just have a burst of power randomly that feels like it should.

Also, it's popping (backfiring/misfiring?) under engine braking quite a lot. It has always done this while I have had it (don't know if that is to do with the aftermarket exhaust) and has always been fine but now seems to be doing it a lot every time I engine brake. If I quickly bring the throttle on and then back down it will nearly always make a bang.

I'm at my university home and the garage and all the tools (I have some basic tools here) are 40 miles away in London so it would be hard to diagnose until I get there. Could it be clogged carbs or fuel line? Or buggered plug(s)?

Thanks!
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Current ride: Ninja 500R

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

Misbehaving at large throttle openings is unlikely to be a carb problem - if they were filthy enough to clog a main jet to the point of not running, all of the smaller bits handling idle and small openings would be totally gummed up.

Likewise I wouldn't expect an electrical problem. At high rpms the alternator is spinning faster and making more power, so a problem with a poor earth or weak battery is more likely to show at low engine speeds.

I would be looking for an air leak, particularly a split inlet rubber. You may need to wiggle the carbs around a bit to find it.

treeno · Crazy Courier Joined: 26 Dec 2012 Karma :

WULFSTAN · World Chat Champion Joined: 18 Sep 2010 Karma :

Tbh this sounds a lot like my gt 550 that had a really bad inlet air leak.
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P.addy · *Formerly known as* P. Joined: 14 Feb 2008 Karma :

Grab a can of wd40 and spray around the inlets while its running, think Robby is on to a winner with this one. Thumbs Up

DrSnoosnoo · World Chat Champion Joined: 28 Mar 2012 Karma :

I reckon an air leak too and agree with the point that if the main jets are clogged the smaller ones would be moreso?
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treeno · Crazy Courier Joined: 26 Dec 2012 Karma :

Thanks guys. What exactly am I looking for? A change of engine speed/sound at idle when I do the spraying? Didn't seem to have much effect (although the idle is usually quite unstable when it's cold so it's hard to tell).
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Current ride: Ninja 500R

P.addy · *Formerly known as* P. Joined: 14 Feb 2008 Karma :

Get it warm then Laughing

Warm enough to idle steady at 1300 or so rpm.

Give the bit between the engine and carbs a quick spray, if the revs change at all, bogs, increases etc then you have a leak there.

treeno · Crazy Courier Joined: 26 Dec 2012 Karma :

Fuck my neighbours are going to hate me. Laughing

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Current ride: Ninja 500R

treeno · Crazy Courier Joined: 26 Dec 2012 Karma :

Okay so got it warmed up, the spraying didn't seem to have any effect on the idle at all. One thing I did notice on the way back from my testing spot was that it seemed to perform much better when hot (unless that was a side effect of all the GT85 I had been spraying), bogging down less. Still lurchy and popping multiple times a second when off the throttle though.
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Current ride: Ninja 500R

treeno · Crazy Courier Joined: 26 Dec 2012 Karma :

Could this be the cause of my problems?!
https://i42.tinypic.com/rwta1f.jpg
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Current ride: Ninja 500R

P.addy · *Formerly known as* P. Joined: 14 Feb 2008 Karma :

Replace that lol

treeno · Crazy Courier Joined: 26 Dec 2012 Karma :

P.addy · *Formerly known as* P. Joined: 14 Feb 2008 Karma :

Could have sucked some of that into the carb... I'd pull em off and just make sure the bowls are clean and jets are clear.

treeno · Crazy Courier Joined: 26 Dec 2012 Karma :

Cheers

.
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Current ride: Ninja 500R

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

The air filter bits won't get sucked into the bits of the carb that gum up - the bits will past right down the middle of the carb and end up in your engine, then come out the other side.

Sort the air filter, see how it behaves, don't pull the carbs apart just yet.

On a more general note, if you ask for help in the workshop the general idea is that you make sure the bike is otherwise serviceable first. It's extremely lazy to ask for help diagnosing a problem before even checking over the basics yourself.

treeno · Crazy Courier Joined: 26 Dec 2012 Karma :

The carbs had chunks of air filter in just about every crevice. I would have checked the air filter sooner but like I said I was away from home without my tools. I mainly wanted to get a general consensus on what the problem was to see if it would be okay to ride it home. Would you like a penny for your wasted bandwidth?
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Current ride: Ninja 500R