Backfiring |
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Kriegmob
Falcone Joined: 10 Aug 2017 Location: Juneau Alaska Status: Offline Points: 38 |
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Posted: 31 Jul 2018 at 03:05 |
hello, my 2007 Nevada 750 just had an oil and filters change. I replaced the spark plugs as well. It’s running real peppy except coasting/ deacclerating in gear it’s backfiring. Sounds like it’s just the left cylinder. I pulled plugs and that one was already showing different wear than the right(good) one. New plug put in, but backfire persists.
Any ideas guzzi-brethren? 🙏🏽
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Adam
Senior Member Joined: 19 Jul 2017 Location: UK Status: Offline Points: 127 |
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If it's on the original plug leads and caps they might be a bit tired and didn't like being disturbed. If possible swap the leads over to see if the fault goes to the other cylinder. Also check the exhaust is secure and sealed.
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GC888
Senior Member Joined: 21 Dec 2015 Location: Manchester UK Status: Offline Points: 174 |
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Backfiring is unburnt fuel.
Following the replaced plugs suggests an electrical issue (as the filter change should have had no effect, you could remove the oil and it would still run for a while) So I'm with the plug cap theory / lead I would check both sparks while moving the cap around (don't electrocute yourself or set any fuel on fire :-)
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Brian UK
Moderator Group Joined: 13 May 2014 Location: Surrey Status: Offline Points: 17641 |
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A leak in the exhaust can also cause this. Worth checking.
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Brian.
Better 5 minutes late in this world than years early in the next. |
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johnno
Senior Member Joined: 19 Jul 2014 Location: loughborough uk Status: Offline Points: 5582 |
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1100 sport corsa , Yam R1, guzzi 650tt rider
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TimmyTheHog
Falcone Joined: 19 Mar 2018 Location: Surrey BC Status: Offline Points: 41 |
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Check your plug & cap and see if there are any carbon formed over connection points & breakage on the caps.
not sure about Nevada, but there is a "common issue" with the V7's cap as well as Griso & Stelvio's. The rubber of the cap will either loosen over time and/or crack thru which will cause arcing. As you just changed your plug, it is likely your caps are loosen enough to not fully establish a good connection which warranted the backfire. My V7 had that issue couple weeks ago and actually misfire enough to toast my cat in the pipe.
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johnno
Senior Member Joined: 19 Jul 2014 Location: loughborough uk Status: Offline Points: 5582 |
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1100 sport corsa , Yam R1, guzzi 650tt rider
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iansoady
Senior Member Joined: 23 Jul 2017 Location: Redditch Status: Offline Points: 2402 |
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Decent NGK plug caps are cheap enough - it's probably worth changing them.
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Ian
1952 Norton ES2 1986 Honda XBR500 1958-ish Greeves/Triumph in progress |
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Ken-Guzzibear
Moderator Group Joined: 13 May 2014 Location: Sileby Leics Status: Offline Points: 9454 |
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Backfiring
Plug caps n leads Alltho' new plugs worth popping old uns back there has been issues with new plugs being faulty Check inlet for any air leaks ...when engine hot a quick squirt of WD40 on the inlet will find a leak engine will inc revs exhaust header or along exhaust check for any leak you ought to be able to hear it / see it. Always check the easy stuff first If still not sorted look hard for any loose/chafed connections in the ign cct After this lot it kinda gets more complicated |
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The Older i Get, The Better I Was
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jefrs
Senior Member Joined: 12 Aug 2018 Location: West Berkshire Status: Offline Points: 333 |
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Having had fun with a Power Commander etc etc on another bike, lessons learnt - Backfiring and popping seem to be a feature of EFI rather than the exception. Deceleration popping is normally rich mix going down the exhaust, but can also be a plug missing (no spark) and doing the same thing (unburnt fuel). They can be very fussy about the spark plug gap, too small and they misfire all over the place, too wide and they miss at higher revs (NB). Any faults with HT lead and/or HT cap will produce missing. Just because it's new doesn't mean a spark plug/cap/etc is not faulty. Murphy's Law applies. Look for the last thing changed before is acted up, it's probably that.
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Kriegmob
Falcone Joined: 10 Aug 2017 Location: Juneau Alaska Status: Offline Points: 38 |
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thanks everyone! To follow up... I’ve replaced that spark plug (checked gap, installed to the letter per the manual) looked at that exhaust manifold and both bolts were loose, one finger loose and wobbly. Tightened those up with big hopes that the issue would be resolved.
Alas, no... So, I was going to ask how to check for a leak, but just read that answer....thanks! Looks like plug wires must be checked. Thanks again!
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jefrs
Senior Member Joined: 12 Aug 2018 Location: West Berkshire Status: Offline Points: 333 |
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It is difficult to check the HT lead. The ones on my V7.ii appear to be silicone type (the insulation). I say appear to be because they are soft and floppy like the lead I replaced onto my other bike. That lead has carbon fibre conductors, which has better conductivity than copper, unlike the useless graphite-string suppressor lead of olde. Silicone insulation is heat proof. The HT lead runs along the cylinder, it gets hot. If the HT lead has plastic/rubber insulation it gets baked and can crack, and then the HT tracks to ground. If the HT lead has gone stiff and hard, it is probably shot. The HT cap on my V7.ii is a 120° rubber job, I have no idea if it is resistive. The spark plug is shown as NGK CPR8EB-9, that "R" tells us it is resistive 5kOhm, the final "9" is trying to tell us it is pre-set to 0.9mm but the manual says 0.6-0.7mm. NGK actually recommend both a resistive cap and a resistive plug. The reason for this is not just radio interference, electronic ignition likes having a load to hold up the charge (coulombs) so that the spark is fatter and slightly longer duration to better ignite the fuel. If you start the engine in a dark shed and can see faint sparks running to ground then the insulation is shot, it cannot be repaired. You had a loose header. This will give you a crude free-flow exhaust system (and fool the Lambda if fitted), it will run rich and probably soot up the cylinder head (the plugs looked different), this can cause missing. It will burn out eventually, use top-end clean burning petrol. You could chuck a generous dose of Redex (or other) injector cleaner in the tank, that usually gets rid of loose carbon quickly; italian tune up.
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