guzziriders.org - moto guzzi forum Homepage
Forum Home Forum Home > Technical > Small Blocks
  New Posts New Posts RSS Feed - Backfiring
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Backfiring

 Post Reply Post Reply
Author
Message
Kriegmob View Drop Down
Falcone
Falcone
Avatar

Joined: 10 Aug 2017
Location: Juneau Alaska
Status: Offline
Points: 38
Post Options Post Options   Thanks (0) Thanks(0)   Quote Kriegmob Quote  Post ReplyReply Direct Link To This Post Topic: Backfiring
    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?  🙏🏽 
Back to Top
Adam View Drop Down
Senior Member
Senior Member
Avatar

Joined: 19 Jul 2017
Location: UK
Status: Offline
Points: 127
Post Options Post Options   Thanks (0) Thanks(0)   Quote Adam Quote  Post ReplyReply Direct Link To This Post Posted: 31 Jul 2018 at 06:30
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. 
Back to Top
GC888 View Drop Down
Senior Member
Senior Member
Avatar

Joined: 21 Dec 2015
Location: Manchester UK
Status: Offline
Points: 174
Post Options Post Options   Thanks (0) Thanks(0)   Quote GC888 Quote  Post ReplyReply Direct Link To This Post Posted: 31 Jul 2018 at 06:45
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 :-) 
Back to Top
Brian UK View Drop Down
Moderator Group
Moderator Group
Avatar

Joined: 13 May 2014
Location: Surrey
Status: Offline
Points: 17641
Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 31 Jul 2018 at 10:49
A leak in the exhaust can also cause this. Worth checking.
Brian.

Better 5 minutes late in this world than years early in the next.
Back to Top
johnno View Drop Down
Senior Member
Senior Member


Joined: 19 Jul 2014
Location: loughborough uk
Status: Offline
Points: 5582
Post Options Post Options   Thanks (0) Thanks(0)   Quote johnno Quote  Post ReplyReply Direct Link To This Post Posted: 31 Jul 2018 at 10:57
Originally posted by Brian UK Brian UK wrote:

A leak in the exhaust can also cause this. Worth checking.
could be a exhaust gasket , your exhaust pipe into engine head.When engine cold on first start up you might hear it 
1100 sport corsa , Yam R1, guzzi 650tt rider
Back to Top
TimmyTheHog View Drop Down
Falcone
Falcone
Avatar

Joined: 19 Mar 2018
Location: Surrey BC
Status: Offline
Points: 41
Post Options Post Options   Thanks (0) Thanks(0)   Quote TimmyTheHog Quote  Post ReplyReply Direct Link To This Post Posted: 31 Jul 2018 at 19:34
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.
Back to Top
johnno View Drop Down
Senior Member
Senior Member


Joined: 19 Jul 2014
Location: loughborough uk
Status: Offline
Points: 5582
Post Options Post Options   Thanks (0) Thanks(0)   Quote johnno Quote  Post ReplyReply Direct Link To This Post Posted: 31 Jul 2018 at 20:14
Originally posted by TimmyTheHog TimmyTheHog wrote:

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.
 worth checking for sure
1100 sport corsa , Yam R1, guzzi 650tt rider
Back to Top
iansoady View Drop Down
Senior Member
Senior Member
Avatar

Joined: 23 Jul 2017
Location: Redditch
Status: Offline
Points: 2402
Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 01 Aug 2018 at 10:10
Decent NGK plug caps are cheap enough - it's probably worth changing them.
Ian
1952 Norton ES2
1986 Honda XBR500
1958-ish Greeves/Triumph in progress
Back to Top
Ken-Guzzibear View Drop Down
Moderator Group
Moderator Group
Avatar

Joined: 13 May 2014
Location: Sileby Leics
Status: Offline
Points: 9454
Post Options Post Options   Thanks (0) Thanks(0)   Quote Ken-Guzzibear Quote  Post ReplyReply Direct Link To This Post Posted: 01 Aug 2018 at 11:39
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
The Older i Get, The Better I Was
Back to Top
jefrs View Drop Down
Senior Member
Senior Member
Avatar

Joined: 12 Aug 2018
Location: West Berkshire
Status: Offline
Points: 333
Post Options Post Options   Thanks (0) Thanks(0)   Quote jefrs Quote  Post ReplyReply Direct Link To This Post Posted: 14 Aug 2018 at 13:28
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.
Back to Top
Kriegmob View Drop Down
Falcone
Falcone
Avatar

Joined: 10 Aug 2017
Location: Juneau Alaska
Status: Offline
Points: 38
Post Options Post Options   Thanks (0) Thanks(0)   Quote Kriegmob Quote  Post ReplyReply Direct Link To This Post Posted: 14 Aug 2018 at 20:44
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!
Back to Top
jefrs View Drop Down
Senior Member
Senior Member
Avatar

Joined: 12 Aug 2018
Location: West Berkshire
Status: Offline
Points: 333
Post Options Post Options   Thanks (0) Thanks(0)   Quote jefrs Quote  Post ReplyReply Direct Link To This Post Posted: 15 Aug 2018 at 03:44
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.
Back to Top
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.03
Copyright ©2001-2019 Web Wiz Ltd.

This page was generated in 0.098 seconds.