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Persistent left cylinder misfire


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Ok, scored a set of vacuum gauges, which has led to some confusion on my part.

Yes, the TBs are out of sync but the good (right) cylinder is hovering around the 200 mark in the red (intake leak warning red). The stumbling left cylinder is at 100. Now that is about the same vacuum I can muster by sucking on the tube myself... what actual vacuum reading should I be seeing, just so I know (even if that is not important at this point!)
if7K7sq.jpg

 

 

 

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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

17 minutes ago, docc said:

No matter the value, they should just be the same.

Phew, well thank you for that. Out of interest is there a value given anywhere for vacuum?

I'm going to sync after I  put fresh rubbers on, my attempt with the silicone has done nothing to help matters.

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The Workshop Manual states the vacuum should be within 5mm Hg (mercury) as I recall. Again, no pure specification, only the maximum allowable variance.

I am not sure of your gauges are already calibrated to display mm Hg? (Seems my Sport pulls the Hg columns into the 50s at around 2500-3000 rpm. 
 

Oh, and gstallons is right on about sucking the mercury. Chopping the throttle from 3000 would be a bad idea! :o

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Oh, and gstallons is right on about sucking the mercury. Chopping the throttle from 3000 would be a bad idea! :o

Well, yeah.. a guy would have to have a clue if he's using them. :rasta::D

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I've got the intake rubber off (fun), and it doesn't seem to have any rips that go all the way through, they're pretty thick really.

The inside of the tb is very dirty behind the butterfly, very grimy, I'll give it a scrub.

I'll stick the new one on when it comes and see, but I don't hold out much hope for it fixing it.

If I'm still stuck after that, can you measure the primary resistance at the ignition lead? Or is it tank off and test the coil off the bike?

Thanks

 

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After you have cleaned trottlebody's and AFC screws, I woud  take OF the trottle linkage, and check TPS,,, like 3 times more,  157mv,,   It's  V imortant... so I've learned.    Then I use a feeler gauge  0.05mm behind each trottle stop screws, and then each screws around a quartof a turn..   Adjust  the trottle linkage with the white knob so it fits perfect on the trottle body.  She can easily have misfires on one side if this is not correct.   My Greenie did.     This doesn't cost anything,,  ah well a few  beer's.   IPA is of big help.

Plugwires 5000ohm.  Basicly every elec connnection needs TLC.       It does feel V good when she is behaving again,   Yu'l find it,   :rasta:

cheers tom.

 

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23 hours ago, Grim said:

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. 

No probs.  I’ll nip down the garage and root them out.

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3 hours ago, stewgnu said:

No probs.  I’ll nip down the garage and root them out.

just realised a typo, it's highboy_coupe@yahoo.co.uk

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On 5/3/2020 at 11:40 AM, Grim said:

 

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

 

 

 

Yes, pull both plug caps

With your multimeter measure the resistance from each plug cap in turn, it should measure the same resistance typically about 8,000 Ohms, same on both sides. This is a combination of cap, lead and coil in series.

Sometimes Guzzi have used that nasty carbon core lead, it can break contact and cause arcing inside the cable usually misses under acceleration because it's harder for the spark to jump the gap under pressure.

Replace with copper core.

BTW you should not have carbon lead in series with a resistor cap and xxxR resistor plugs, you only need one resistor.

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Have you done a compression check? Maye it's not fuel or spark. Easy enough, in any case.

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Indeed, if compression and spark are fine, and manometer/tps readings et al are within spec, you could also think about having the injectors pulled and ultrasonically cleaned.

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23 minutes ago, po18guy said:

Indeed, if compression and spark are fine, and manometer/tps readings et al are within spec, you could also think about having the injectors pulled and ultrasonically cleaned.

I have yet to test compression, I will try to get that done.

 

12 hours ago, Kiwi_Roy said:

With your multimeter measure the resistance from each plug cap in turn, it should measure the same resistance typically about 8,000 Ohms, same on both sides. This is a combination of cap, lead and coil in series.


The spark plugs read 8300 Ohms on the right, and 7900 Ohms on the left, is this cause for concern (this is with brand new plugs).

 

I set the throttle stops as per the feeler gauge method and then connected the rod, the balance was off, but could be brought level by using the air screws. This did not work when winding them out the same amount, but through doing each side individually I could get the vacuum level to sync up.
 

All the way through this the right hand cylinder is just chuffing away beautifully, never faltering, and the left is stumbling away. I did a little video:
 

https://www.youtube.com/watch?v=ZeR9KYqC2pA

 

 

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400 ohms , not enough to worry about adjust the linkages as I described earlier . you are wanting the base throttle plate angle to be identical .

 

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26 minutes ago, gstallons said:

400 ohms , not enough to worry about adjust the linkages as I described earlier . you are wanting the base throttle plate angle to be identical .

 

I did use the method you described, with the rod connected the feeler gauge set just slides out of the throttle screw/plate on the right hand side.

One thing that was tricky here, the white nylon knob is very tight, and doesn't really allow any adjustment ( it tries to spin the ball joint on the right).

I took off the e-clip on the left and then got the thing to line up that way, then wound it a little more so when the rod was connected the feeler gauge fell out on the right.

At that point (the tps was reading 550mv) connecting the vacuum gauges up gave pretty much the same reading as before, so I opened up the air screw (both were fully closed) 'till they were balanced.

Still got that weak left hand pot, maybe it is compression, I'll get a tester tomorrow.

 

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