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Discussion Starter #1 (Edited)
Went to install a new MWR air filter yesterday, among other things, and when I pulled the old air filter out, I was dismayed to see that it had heat damage on the back side (that faces the throttle bodies), isolated to the left side. I assume this means that my #1 and #2 cylinders are backfiring into the intake, but troubleshooting what might cause that is beyond my scope of knowledge. Any help is appreciated.

other things that may or may not be helpful to know:
- bike has ~6,600 miles on it
- all stock as far as air/fuel/engine go, although I'm installing a de-cat midpipe now and am waiting on a microtec that I ordered from x-bikes.
- I have no idea how old, or what kind, this air filter is that I removed from the PO
- I get after-fire (or whatever the correct term is that people mistakenly call "backfiring" out of the exhaust); loud popping out the exhaust on over-run when riding hard in the canyons. It's much louder and sharper, like a gunshot, than I had out of my SV650 that had an aftermarket slip-on exhaust. I had chalked it up as a normal characteristic of the F4 engine based on this thread: http://www.mvagusta.net/forum/showthread.php?t=54663&highlight=backfire
- sometimes have a delay in throttle response opening it up from closed-throttle. It's akin to how turbo lag feels in a car if you are stopped/barely moving and floor it--it's not that it doesn't respond right away, it's that it responds lethargically for the first few moments until the engine winds up further
- sometimes I have a sound like air pressure releasing (like a weak un-corking of champagne). I can't tell exactly where it is coming from, but it's in front of me and near the top half of the bike. This happens if I let completely off the throttle and start lightly braking/coasting from the engine being in a mid to high RPM range, such as when I see a light turn red far ahead of me and leisurely slow down to stop. Once the revs have dropped low enough to downshift, I'll blip the throttle and to shift and the "puffing" sound happens at the exact moment I go from off-throttle to on-throttle during that downshift. If I'm riding aggressively or go way overkill on how hard I blip the throttle to downshift, then the noise doesn't happen
- getting terrible gas mileage and smells like it's burning extremely rich. Gas light on at 80-85 miles of commuting in traffic, sometimes bone dry by 100 miles. Figured much of that would get sorted with the microtec

Old filter, this is the front side:


Back side


Detail. Aside from the melting filter element, notice the heat damage on the plastic rail
 

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Your fuel consumption is about standard for a Brutale S....

The noises from your exhaust are not...

Valve clearances or cam timing out ?
 

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With a bike that's 10 years old, I'd be looking for vacuum leaks too. Spray, with carb cleaner, every joint and vacuum line from the air box right on down to the cylinder head. Do this with the engine running, if a leak is present, the engine should speed up briefly. Focus on #1 &#2 first , some areas are going to be impossible to get at without moving the tank. This is just one thing you can do yourself before taking it to a shop. Other than that, it could be any number of things, which get more evasive.
 

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Remember the bike leans left when on the side stand.....fluid accumulation in the air box (oil mist from breather) is going to be predominantly on that side. Could be part of the reason for deterioration on that side of the air cleaner.
After fire on decel (popping sound) is unburned fuel igniting in the exhaust. My 910R gets 120+ miles on a tank at normal commute or easy riding. Sounds like yours is running very rich....and excess fuel blow back into the air box could be causing that air cleaner deterioration as well (remember, leaning left on side stand and accumulating in box).
Just my 2 cents worth and about that valuable, too.
 

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Discussion Starter #7
brainstorming

- I don't want to install the MWR filter until I know it won't get damaged, but if I find something that I think might be a fix, I don't know how I can verify it other than "guess and check". Suggestions?
- I want to rule out simple/dumb things before throwing money at the dealer unnecessarily, and also try to determine if it's something mapping related that working with the microtec will be able to iron out.

Going to take the spark plugs out ASAP this week and check their condition, that may help point to something

- I was already talking with Pro Italia about the next service interval (which they do between 6,000 and 7,500 miles); what I could do myself vs what I need them to do. The work that they were going to do covered valves, clean/adjust throttle bodies, and TPS reset in preparation for me to install the microtec

Valve clearances or cam timing out ?
Valves were already on the list to be done anyways. I'll check with PI to see if the cam timing is something included in their scheduled maintenance

From memory, exhaust pop is running too lean, carb pop is running too rich. Also check the exhaust for leaks at header and other joints.
Is it possible to have two cylinders running lean--and popping out the exhaust, while the other two are rich and backfiring?

With a bike that's 10 years old, I'd be looking for vacuum leaks too. Spray, with carb cleaner, every joint and vacuum line from the air box right on down to the cylinder head. Do this with the engine running, if a leak is present, the engine should speed up briefly. Focus on #1  first , some areas are going to be impossible to get at without moving the tank. This is just one thing you can do yourself before taking it to a shop. Other than that, it could be any number of things, which get more evasive.
This will be the next thing I try after checking out the spark plugs. I removed the carb canister (which on this bike was actually on the outside of the tank, right above the starter) and getting rid of that simplified things a bit. Just to clarify if I'm looking at the parts fiche as a guide, this basically covers the territory that I'm inspecting/spraying joint by joint, right? (including the 4 lines running from the base of the manifold to where they are vacuum capped on the side of the frame)



Remember the bike leans left when on the side stand.....fluid accumulation in the air box (oil mist from breather) is going to be predominantly on that side. Could be part of the reason for deterioration on that side of the air cleaner.
After fire on decel (popping sound) is unburned fuel igniting in the exhaust. My 910R gets 120+ miles on a tank at normal commute or easy riding. Sounds like yours is running very rich....and excess fuel blow back into the air box could be causing that air cleaner deterioration as well (remember, leaning left on side stand and accumulating in box).
Just my 2 cents worth and about that valuable, too.
Ed, you undersell your experience. This is exactly the kind of potentially simple thing I want to rule out first. And I know the old owner didn't ride too often--only 5,500 miles on the bike when I got it. That's a lot of time on the sidestand. I think looking at the condition of the spark plugs could point to--or away--from something like this. If all the spark plugs were in the same condition, wouldn't that support this theory that the burning air filter is being caused by something after the spark, such as accumulated residue fluid on the left side of the air box?

Also, I don't think this is related, but I'm replacing the breather hose anyway cause it's cracking badly at some of the bends.
 

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Discussion Starter #8
I don't know whether this might be any indicator, but I currently have the exhaust off to install the Arrow midpipe, and pulled the headers off this morning to have a look at them. When I look up into the exhaust outlets on the cylinder head, the 1 and 2 cylinders have more charring and carbon buildup than 3 and 4. Could this further point to richness in 1 and 2?
 

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Yes, It could, and does.
A synchronization of your Throttle bodies might help as well as a dyno tune of your ecu.
 

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A few thought in no particular order...
The exhaust port buildup could also be burnt oil. It will be interesting when you pull the throttle bodies and look down the inlet ports at the back face of the inlet valves.
Tps reset will be required after the microtec install.
The new air filter will change the airflow, and probably lean things off.
Don't forget to check the caps on the throttle body sync hoses, they are well known as a source of air leaks.
 

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Sounds like it would be unsync'd throttle bodies. I wonder if the PO had it serviced somewhere that they adjust the right side, reset the TPS and that was that. My guess is that your #1 and #2 spark plugs will also show signs of running rich.

You may want to just take the hit and get Pro Italia to do the full 7,500mi/12,000km service. At least that way you should get some coverage if something fouls up or runs poorly after they give it back.

Good luck, hope it all resolves into a great working bike.
 

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Discussion Starter #13
A few thought in no particular order...
The exhaust port buildup could also be burnt oil. It will be interesting when you pull the throttle bodies and look down the inlet ports at the back face of the inlet valves
Hopefully get to that point this weekend. Anything in particular I should be looking for around the valves?

Tps reset will be required after the microtec install.
After--good to know. I'll make sure to have the correct order of operations worked out with PI on that

Don't forget to check the caps on the throttle body sync hoses, they are well known as a source of air leaks.
I actually just put these caps on when I removed the carb canister (US model) on Sunday. I'll double-check they aren't leaking, but that's not the source of the issue for sure. The other ends of the hose, connected to the intake manifold, could be.
 

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Discussion Starter #14
- spark plugs are all consistent. They look like things are burning rich (no surprise given the exhaust smell), but it's consistent across all cylinders
- looking down the throttle bodies, I didn't notice anything that struck me as alarming or inconsistent between the cylinders, but I'm also treading into territory I don't know anything about here and wouldn't even be sure what I'd be looking for

I have my gas tank put back together with new fuel lines and metal fittings. Letting it sit overnight with some fuel in it to be certain nothing is leaking, then this weekend I'll pop it back on the bike and check for air leaks

Beyond that, I'm going with Reckler's suggestion:

...You may want to just take the hit and get Pro Italia to do the full 7,500mi/12,000km service. At least that way you should get some coverage if something fouls up or runs poorly after they give it back.
I'm still waiting on delivery of the ECU from X-Bikes, but I hope to have that installed before I take the bike to PI. I'm doing all the parts of the 7,500mi service that I know I can do without adult supervision (and without paying someone), but I'll have them check valves, throttle balance, CO, and TPS reset (or I'll do that myself with the Microtec software). All things I want to learn about and be able to master someday, but I want to start with a blank slate done by a professional
 

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Is that about average for a 910? 120 miles/ 190kms per tank?
I can't speak for everyone, and everyone has their own right wrist to deal with.....

I average 30+ miles per gallon most of the time. I set a trip meter when I fill up and start looking for gas stations and a low fuel light when I get around 120 miles.

Have gotten 35 mpg while leisurely ridding rolling country roads on a nice fall day. But I have also seen 25 or less when being aggressive in the mountains...even worse on the track.
 

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Gonna follow this thread since I experience the same 'air leaking sound' exactly as you describe it! Don't have any of the other problems so that might be an ensuring thought that this probably has nothing to do with it.

However, I do like to find out what causes that sound..
 
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