New Failure Mode?

[Guest Mattress]

At somewhere around 2700 miles on my 04 cafe sport, the throttle body on the left cylinder came off of the intake. The entire hose to intake, clamp and TB came off and was at rest on the manifold rim but miss-aligned slightly.

 

The situation: On my way to MGNOC Iowa Rally and had to slow down suddenly from interstate speed for a toll booth. Slowing down was with brakes and engine braking (somewhat heavy). Cut off the engine to fumble for money. Hit the start button and surprised by loud backfire, continued on and heard what I thought was exhaust leak (high pitch whistle).

 

As I had gone over all the bolts before leaving and including exhaust clamp, I was fixated on the trouble being the exhaust. I had noticed evidence of small pinhole leak around an exhaust clamp. Anyhow, I finally notice the problem and it was a simple fix.

 

I tightened up the band clamps and I take it easy on the engine braking. I believe it was a possible combo of poor assembly torque on clamp, or vibrated loose clamp, and backpressure that popped it off.

[Guest ratchethack]

Mattress, the rubber compound of intake boots is susceptible to uV, ozone, and other forms of airborne attack by pollutants. Certain kinds of cleaners and "preservatives" have proven to deteriorate them fairly rapidly. Over time, the clamps often seem to "loosen", when in fact it's the compound itself shrinking. For this reason, the clamps should periodically be checked for tightness. On the other hand, as The Weej has pointed out, getting them too tight can be a bad thing, as in the case of a backfire, if the boots can't pop off to relieve the pressure as yours did, a backfire can bend a throttle butterfly.

 

IMHO, after the boot has popped off and been re-installed, it's a good practice to balance the TBs, as the balance can be knocked out of whack. When this happened to a Pal's Le Mans, it had a new engine vibration that continued until we re-balanced it.

[Martin Barrett]

Very common occurance.

 

Heres Antonio assisting Jaap remount his on the German Treffen this year

 

and yours truely remounting his last year

 

It always seems to be the left.

 

I had a spate again this year and ended up spliting the rubbers I over tightened it and perhaps hadn't quiet got the clamp fully over the stub.

 

It has been said it's a good thing that they do pop off as means the throttle plate won't get bent.

I don't know what the actual cause of the initial backfire would be and if is anything to worry about, I supose it would depend on it's frequency.

 

EDIT - There you go two similatious posts agreeing in principle

[badmotogoozer]

Mine was a regular backfirer until I got it semi-sorted. Would blow TB's off and would also blow the little capplugs zip tied on the intake ports. Now it just backfires here and there when down really low in revs. More sorting to come...

 

Rj

[Guest Nigelstephens]

My Sport 1100 i would do this if the TPS setting was out.

 

The only other example I can think of was on a Rover 800 car that was converted to LPG.

It would do this if the there was an ignition fault due to faulty leads or plugs.

I replaced them and it never happend again. I realise it is completely different situation but there might be some possibilities for you to investigate.

 

I would check plugs, caps and leads just in case.

[Guest Gary Cheek]

Nope! It isn't at all new, nor is it neccessarily a Guzzi failure.

I have had it happen twice. Both times on EFI Guzzis. Once it was a 1993 Cal III EFI. I merely turned on the key and it went off like a cannon! The second time it was on my 2002 Scura, just a backfire through the carb while cranking and pow, off goes anther throttle body.

 

NO it doesn't neccessarily indicate anything wrong. Other than possible operator error.In the case of the Cal III just turning on the ignition can initiate a maverick spark under the right (wrong) conditions. If there is a suitable mixture present and an open intake valve BANG! The fact yours went bang when you turned the engine off and on says it is most likely a maverick spark. The High voltage is still generated in your V11 in the same basic manner as with points. Turning the primary on or off can create the collapsing manetic field that induces a current flow in the secondary of the coil. Sufficient magnetic flux equals spark, air fuel mix equals rapid combustion (explosion) open intake and closed throttle equals something has to give, In this case the rubber joint. Severe backfires can and will bend throttle plates too! So the rubber boot letting go may have been better than the alternative.

 

This is why engines have been known to start without cranking. Just turning on the key with the rare chance every thhing is perfect and one cylinder fires , the engine starts and runs without cranking.

Extremely rare now days but it can happen.

 

If ithe backfire occurs while actually running there are other places to look and this is not normal. Mixture , timing , valve lash and especially the magnetic timing pick up need attention. An improper gap, loose or corroded connection or a piece of foreign metal stuck to the probe could be a cause.

 

Probably won't happen again but check it out.

[quazi-moto]

It happened on my '02 LeMans a few times, but always on the right side. If the EFI wasn't so lean it probably wouldn't backfire at all.

[richard100t]

This has happened to me a few times as well. Its important to put the intake sleeves on properly for one thing. The main problem that was causing the sleeve to pop off was unbalanced tb's causing the engine to run rough. All the other posts sounded exactly like what happened to mine. It would stay on at speed, but once I let off the speed & slowed down the engine would backfire & off would come the left side sleeve. Always the left side & never the right side. I took my bike to my dealer a few months ago & he checked it out, balanced the tb's. After that the bike has run like a dream & the sleeve stays put right where it belongs. Maybe someone with better writing skills could post a few lines on the proper way to attach the intake sleeves to the tb's? Also check the valve clearances & spark plug gap etc...

 

I have been wanting to remark lately that since the weather has cooled off my Guzzi has been running extremely well and smooth. It has 14k miles on the speedo & runs better than ever. No major problems that some tweaking and adjustments couldnt take care of so far. I have seen several posts lately of bikes with multiple expensive breakdowns and various problems. I would like to knock on wood and just say that so far I think the factory workers must have been just the right amount of drunk the time they put mine together! When my v11 goose is in proper tune & set up right I dont think theres another bike out there that I'd rather ride. It turns heads & performs just well enough for the type of riding that I normally do.

[docc]

I think the factory workers must have been just the right amount of drunk the time they put mine together!

 

 

Ah! And the trick is to maintain that level during the required service intervals. My sport appears to perform better on service conducted with single malt scotch. Your Rosso may like Chianti. Or even Grappa, but watch out for the terrific vertical nystagmus as it makes the volt-ohm meter hard to read . . .

[Guest Gary Cheek]

The backfire problem posed by the thread starter seems a bit different than most mentioned here. Most of the problems mentioned here are during the normal throttle changes involved in riding the bike. There are numerous possibles for that to occur. Balance, timing, timing probe, mixture, imbalance etc.

 

In this felow's case it was very likely the turning off and quickly switching the ignition back on that caused the backfire. This can occur even in a perfectly timed, balanced, tuned V11.

[Guest Mattress]

Thank you for the very informative replies. I'm happy I actually initiated a useful thread. I thought I would post it in case any new Guzzistis are on the road and suddenly find themselves running rough with a backfire. I for one panicked and assumed it was something serious the Italian gods made happen to cancel my trip to my first Guzzi rally. I didn't even scope the TB at first.

 

Also another symptom: I had lost full lock on my throttle because when the TB disassembled itself from the intake the butterfly cable actuator was making contact with the engine at 1/2 opening.

 

I'll make it a point to check the balance soon. The engine ran fine the rest of the way...

 

I think it was partly due to my heavy use of down shifting and engine braking from 65mph to toll booth stop.

[docc]

 

I think it was partly due to my heavy use of down shifting and engine braking from 65mph to toll booth stop.

 

 

She ought to do this happily. Thge fabulous engine braking down through the gears is one of the things I love about my Guzzi. I think it may be where a lot of my rear tire goes.

 

The backfire is an ill. Jeff's tune-up is the cure.

[Guest Gary Cheek]

In YOUR case;

The heavy downshifting set the backfire up. The turning off and on again the ignition was the cause. Not turning the ignition off and on is the cure.

 

The bike wasn't ill and did nothing unusual, subjected to those conditions. The healthiest bike on the block can do it when the key is cycled in that manner.

 

Both of the times I had a TB pop off of the engine it was related to switch cycling. It can create a spark and with the right condiitions a big backfire. My Dyna equiped Cal II will often fire when hot and I turn the key on. Usually it is on compression and the engine will just rock over.

[robbiekb]

hahahahahahaha sorry to hear that but yeah its regular. last summer i was remounting mine during pretty much every ride until i replaced the rubber mounting boots.

 

dont sweat it and go ride !