1200S Cylinder Temp Disparity

[SDA]

About 1000 mi. ago I noticed the left cylinder of my '08 1200S is running about 50° hotter than the right cylinder. I checked the temp. after noticing different header color after a particularly long, fast ride in near 100°ambient.

The bike has 5000 mi. on it and I feel reasonably confident that I would have noticed the differing header blueing had it been there before but can't be sure. In earlier miles the bike was put through longer and faster rides in even hotter weather and even a bit of track time and I don't think the the headers were showing different colors.

Except for an ECU re-flash from Todd, the engine is stock. (No Todd, I have not gotten around to installing the PCV and Autotune yet). Cyl. temp. disparity was occuring before ECU re-flash. I have the PCV and Autotune but have held off installation not wanting it to mask some mechanical problem.

I'm checking the temp. with an infra red at the exhaust port finning. Ambient temp. for tests have been 85°-100°. The left to right disparity is always 35°-50°- regardless of engine load used for test. High reading recorded for hot cylinder: 340°; cool cylinder 295°. As this represents roughly 25% of the ambient temp./working temp. differential I'm thinking it is significant enough to say that there is something amiss.

TPS has been reset using VDST. Valves are adjusted (toward tight side of specs.) Throttle bodies are synced. Cylinder leakdown tests a perfect 100% for both cylinders (yes, I'm sure it's leaking some, but not enough to register on my Snap-On tester)

Do I have a problem?

Could it only be a fueling or timing problem or could it be something mechanical?

Since I think it is a new problem I tend not to suspect cam timing (cam mfg. defect) but......?

Could the installation of the PCV and auto tune correct?

How could the PCV and auto tune correct when there is only one common O2 sensor?

 

[john zibell]

It sounds like you may have an injector that is delivering too much to too ltlle fuel. I would recommend removing them and sending them to a shop that specializes in reconditioning injectors. Be sure to tell them about your observations so they can check the amout of fuel each injector passes.

 

[SDA]

Thanks John,

Care to recommend an injector service company?

I found OKinjectors in Oklahoma w/google. Looks they're outfitted well but who knows what they're service is like.

 

[Rafael]

If it turns out to be a clogged injector, changing the fuel filter would be next to do.

Before sending them off to the shop, a simple test would be to switch them and see if the symptoms follow.

 

[SDA]

But of course!

Thanks for the "DUH" Rafael.

I'd like to think I'd have thought of that myself if I got to tinker more but maybe not since I've had this problem for 3 months and hadn't thought of it yet.

 

[ghezzi]

Every V-Twin with a single airbox and a single O2 sensor will have the same problem.
Reason, uneven induction pulses. Left cylinder intake ................. 270 degrees crank rotation and right cylinder intake ............................ 450 degrees crank rotation before the left cylinder swallows another portion of the atmosphere.

With a single O2 sensor the ECU has to average out the air/fuel ratio, therefore the left cylinder getting more air will run leaner/hotter.

Some bikes will have a very large airbox with a divider in the middle. Suzuki RGV/Aprilia RS250 uses a divider on their 90 degree V-Twin 2 stroke water cooled engine, yet each carb is jetted differently.

If you seek perfection for your Guzzi, then have an O2 sensor bung inserted in each header pipe about 6" from the port and have your bike dyno tuned with individual maps for each cylinder. My Bellagio has 24% extra fuel R/H side but 42% extra fuel L/H side at the same point after pipe and airbox mods.

 

[SDA]

Wow Ghezzi!

It certainly sounds like you win the prize. Very interesting stuff. Even if you were off your rocker, sounds like a sensor for each cylinder is worth the effort.

I'm going to contact Todd about a couple of bungs and a 2nd wide-band O2 sensor to go with my PCV and auto-tune.

Valuable stuff, all of you.

Thanks,

 

[Rafael]

Every V-Twin with a single airbox and a single O2 sensor will have the same problem.
Reason, uneven induction pulses. Left cylinder intake ................. 270 degrees crank rotation and right cylinder intake ............................ 450 degrees crank rotation before the left cylinder swallows another portion of the atmosphere.

I don't get it. :huh: well not yet. Wouldn't the right cylinder have to rotate the same amount to get another gulp too? Is there a a slight vacuum present in the box when the L cylinder takes in air? The Quota has an divider in it's air box too.

Anyway, SDA, now you have to swap the injectors - you have 2 hypothesis to test. Forget the fuel filter... except if you still have the half plastic OE unit, put that on your winter to do list.

 

[Mi_ka]

I read about the Honda new NC700X 270-crank in-line twin having slightly different cam shaft lobes per cylinder for this exact cylinder input balancing reason.

Also, isn't the new single body small block engine of unequal length input tube design?

I *think* that the exhaust pulses must be taken into account too - one cylinder looking at higher pressure on its exhaust phase than the other so exhaust scavenging differs a bit.

 

[john zibell]

If it does turn out to be an injector problem, I've used this shop in the past with good results. http://www.rceng.com/

 

[SDA]

Thanks for the source John.

So manufacturers spend all that time and under tank space to create air box resonance that is only optimal for one of the cylinders, or perhaps, one of the cylinders in one RPM range and the other cylinder in a different RPM range? Do I understand that right?

 

[ghezzi]

I did the infra-red temp test on my old Cali Stone and it had about a 20degree Celsius difference between cylinders.

Many air cooled in-line V-twins ran different jetting in each carb, and I like most people assumed it was because the rear cylinder was bathed in hotter air. Buells have a fan behind the rear cylinder.

Never have I encountered a parrallel twin with different jetting for each cylinder, either 2 stroke or 4 stroke.
Yet every 2 stroke V twin has different jets for each carb (using a single air box). Yet cylinder temps should be identical with efficient water cooling. So one cylinder must be running leaner than the other.

Theoretically, Guzzi cylinders cop the same amount of air flow so should run the same temp.
Carby models with individual K&N air cleaners (ie. 850-1000 Le Mans) should run equal temps.
I bet those still running standard air box/filter will have a temp difference. Inside the Cali/Bellagio air box the two bellmouths of the inlet trumpets face across each other and almost touch. On inline fours or parrallel twins the trumpets run parrallel to each other. A giant air box for your Guzzi with a massive divider would alter things dramatically.

Guzzi's typically use a very small airbox, my Cali and Bellagio have the same of approx 2 litres capacity.
High performance bikes (2 or 4 cylinder) typically have air boxes up to 15 litres in capacity to create as much still air as possible. This aids horsepower/torque as well as efficiency (EPA) but the inlet trumpets on many 4 cylinder bikes are unequal in length. This is to balance air speed/volumes to each cylinder so only one O2 sensor/fuel map is required for all four cylinders.

Back to Guzzi's, Todd has proven there are midrange power/torque benefits to be had by retaining the standard air box (just remove lid & retune), because it aids a still air environment compared to the turbulence encountered in the inlet tract when pod filters are used at the throttle body.

 

[ghezzi]

Rafael, it is hard to draw pictures with a keyboard but I will try.
Left inlet valve begins to open and the cylinder draws in air rapidly from my 2 litre air box via a 40mm throttle body.
Left inlet valve stays open for say, 280 degrees of crankshaft rotation (cam timing of 70/30).
Yet the inlet valve for the right cylinder will start to open only 270 degrees of crankshaft rotation after the left valve started its opening cycle.

This now means both inlet valves are open together for at least 10 degrees of crankshaft rotation, but because these two 40mm throttle bodies are much larger than the two 25mm holes of the airbox inlet snorkels, we may end up with a partial vacumn in the air box for a short period of time. This just happens to be when the R/H cylinder is wanting its share of our atmosphere.

If we continue the cycle, both inlet valves will be closed for approx 260 degrees of crankshaft rotation before the left inlet will want to start opening again. So my pissy little airbox gets a short reprieve to fill itself up with fresh air.

Now calculate the time it takes in milleseconds for all this to take place at 6,000rpm. Thats 360 degrees of crankshaft rotation (half of the 4 cycles/strokes) @ 100 times per second, don't forget we have to squeeze in the exhaust valve operation within that second, with 50 suck, squeeze, bang & blow cycles within that second. That ain't much time to fill your lungs Henry.

As the old sullidge pump ain't that mutch of a performance engine, it don't mean shit!