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Persistent left cylinder misfire


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Hi, I realise that misfires are very common forum fodder, I have read as much as I can before posting, I apologise in advance..

It's a 2003 sport, still with external pump and filter.

What I thought was a random misfire at idle when hot is actually a persistent misfire on the left cylinder.  

Originally the valves were tight, I have tried the valves at .004 and .006, now set to .006 and .008 with no real difference.

I tried new plugs (gapped) and I have checked the leads for corrosion.

I have just done  a TPS reset. It was at 85mv fully closed, it is now at 157mv.

Air bypass screws are 1 turn out

Idle is at 1300rpm

On idle if I go to the back of the bike, the right hand exhaust gives a consistent rythmic slap if you put your hand gently over the can. The left hand side is weaker and faltering, kind of "off beat".

At the tachometer needle kind of wobbles a bit at idle, if you rev it to 3k you can hear misses and the tacho jumps around a bit more. There are no backfires at all.

Can I test the coils on the bike without taking the tank off again?

I know these threads never get resolved, and I appreciate that misfire diagnosis through a forum is not the most realistic expectation, I am just at my wit's end, and I have probably missed something.

 

Thanks

 

 

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Oh, bugger. It's idling over 1000 on the tacho, haven't checked in GuzziDiag. Might have to go over this again.... Have I invented a new procedure, BTW? 😉   Thanks for all your help.

Do it now while they can't come over . . .  

Hi Grim, I know I'm late to the party but FWIW my '02 Scura would backfire then spit off the RH inlet rubber after 100 miles. Replaced the inlet rubber & issue resolved, even found the low fu

39 minutes ago, Grim said:

Hi, I realise that misfires are very common forum fodder, I have read as much as I can before posting, I apologise in advance..

It's a 2003 sport, still with external pump and filter.

What I thought was a random misfire at idle when hot is actually a persistent misfire on the left cylinder.  

Originally the valves were tight, I have tried the valves at .004 and .006, now set to .006 and .008 with no real difference.

I tried new plugs (gapped) and I have checked the leads for corrosion.

I have just done  a TPS reset. It was at 85mv fully closed, it is now at 157mv.

Air bypass screws are 1 turn out

Idle is at 1300rpm

On idle if I go to the back of the bike, the right hand exhaust gives a consistent rythmic slap if you put your hand gently over the can. The left hand side is weaker and faltering, kind of "off beat".

At the tachometer needle kind of wobbles a bit at idle, if you rev it to 3k you can hear misses and the tacho jumps around a bit more. There are no backfires at all.

Can I test the coils on the bike without taking the tank off again?

I know these threads never get resolved, and I appreciate that misfire diagnosis through a forum is not the most realistic expectation, I am just at my wit's end, and I have probably missed something.

 

Thanks

 

 

Does she charge good ?  

Cheers tom.

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Thanks, Charging was around 13.8v last time I checked, the battery was allowed to run down during the current lockdown, the bike has not been in use for a few months.

I charged the battery back up and it started the bike ok. But I have not checked charging since. I will do that.

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I've had minute intake and/or exhaust leaks do that to my Sport (among myriad other things).

You didn't mention CO Fuel Trim setting or throttle body synchronization . . .

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10 minutes ago, docc said:

I've had minute intake and/or exhaust leaks do that to my Sport (among myriad other things).

You didn't mention CO Fuel Trim setting or throttle body synchronization . . .

Thanks, the CO trim was zero in Guzzidiag when I checked, one thing I'm not clear on, does this change with engine temp? People say to zero it AT 60 degrees, my zero setting was seen with the bike cold.

I have not altered the sync of the tbs yet, I don't have a nanometer.

My Tb to head rubbers are definitely old and crusty, but I don't see any rips.

I have a Mistral crossover, there is definitely some chuffing on both sides at the downpipe join, but as the right hand cylinder runs beautifully I wasn't to worried, I do have exhaust gasket sealant if you think it will help?

 

 

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So, the CO stays the same, just that the engine has to be operating temperature to change it using guzzidiag.

A throttle body synch would likely works wonders. You could score TwinMax or equivalent in lieu of some kind of manometer or "carb sticks."

I saw a pretty impressive improvement from "grooming" my exhaust and tightening up all those leaky joints. There were only a couple sooty ones and they weren't bad, so it surprised me when it made a noticeable difference.

Seriously, though, buddy, gotta synch those throttle bodies!

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15 minutes ago, docc said:

Seriously, though, buddy, gotta synch those throttle bodies!

If I get a manometer, can I just sync at idle or do I HAVE to do it at 3k? My neighbours are going to love me ...

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12 minutes ago, Grim said:

If I get a manometer, can I just sync at idle or do I HAVE to do it at 3k? My neighbours are going to love me ...

Do it now while they can't come over . . . <_<

 

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Okay, seriously, yes: synch the throttle bodies "at some rpm." Doesn't have to be 3k, but definitely not at idle unless that is where you expect to operate the engine most of the time. I tried synching at 4,500 once and the Sport spit my (former) voltmeter off onto the floor . . .  :o

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3 hours ago, Grim said:

If I get a manometer, can I just sync at idle or do I HAVE to do it at 3k? My neighbours are going to love me ...

You use a manometer with mercury and you will see the mercury disappear at the first blip of the throttle ! 

 P.S. any fluid will do the same thing .

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12 hours ago, Grim said:

If I get a manometer, can I just sync at idle or do I HAVE to do it at 3k? My neighbours are going to love me ...

It only takes a minute Grim, if you’re concerned about your neighbours you’re probably a ‘good neighbour’ yourself and hopefully they’ll understand?  You could knock on and explain the  reasons for the ensuing italian music.

Incidentally, I think i have a few intake boots spare- if you’d like i could post a couple down to you?  

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15 minutes ago, stewgnu said:

It only takes a minute Grim, if you’re concerned about your neighbours you’re probably a ‘good neighbour’ yourself and hopefully they’ll understand?  You could knock on and explain the  reasons for the ensuing italian music.

Incidentally, I think i have a few intake boots spare- if you’d like i could post a couple down to you?  

Ah, that would be brilliant Stew, I spent last night coating my old ones with silicone in attempt to seal up any hidden leaks...

Do you want to invoice me with PayPal? (highboy_coupe@yahoo.co).

 

Re: the neighbours, Yeah, I have young kids and I'm aware of other young families and how loud a stationary Mistral equipped V11 can be. 

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12 hours ago, gstallons said:

You use a manometer with mercury and you will see the mercury disappear at the first blip of the throttle ! 

 P.S. any fluid will do the same thing .

I've been using one since the Pleistocene without that issue. :oldgit:

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Well , you didn't loan yours out either . I wasn't there to see how it happened and I got everything back but the Hg .  

Did you keep the Flintstone mobile dialed in ?

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