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Discussion Starter #1
My bike has developed a stumble coming on at about 5500 and clearing by 8000rpm. It runs fine at idle and revs out fine from 8k to redline. I tried pulling the fuse out of the power commander, but it didn't make a difference. My bike already has iridium plugs and the simplified fuel lines with a new filter in the tank about 4k miles ago. It ran fine until recently and the stumble seems to be the only problem. Before I start throwing parts at it is the anything that might cause a 100% repeatable predictable misfire at a specific rpm only? I am about due for a valve check and maybe a throttle balance but this seems like a fuel or ignition problem as the misfire returns on decel, and there is a lot of popping which it never did before.
 

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Hi Al! How many miles total on the bike? Have you had the valve adjusted before? And, finally, is is starting OK or is it getting a bit hard to start?
 

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Discussion Starter #3
Hey chuck! Just about 15k now. Valves were done at 7500, no adjustment needed. It's on my to-do list to check again shortly. The bike starts up perfectly and seems to run fine everywhere else, which almost makes me discount an air leak of some kind, though I'm not discounting anything at this point. If I had to guess, I'd say it feels like too much fuel, it feels like its loading up on fuel right at 5500 and on decel in this range it's popping a load of flames out the pipe
 

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Interesting. If it were getting hard to start, I'd say valve adjustment. Keep us posted and I'll think on it a bit.
Happy Easter!
 

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Discussion Starter #5
The valves checked out, throttles were a tiny bit out of balance 1-2 vs 3-4, and I reset the TPS very carefully, for shits I put new plugs in too. Its running better but there is some issue with the mapping.

I'm pretty sure the timing is jumping around to sections of the map where it shouldn't be. The last time I rode it, it was idling at almost 2000, but if i tapped the choke lever up and back down the idle would settle. The mechanicals and TPS show the throttle is fully closed when its idling high, so I assume its timing related. I might have a bad TPS or other sensor. Steady state throttle cruising is pretty much unrideable now.
 

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Did you check the coils.
My Brutale 750 has had similar symptoms when only one coil was partially defective.
 

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Hello to everyone!

I have the same problem with my Brutale 750s (MY'04). It stumbles from 10000 until 11500rpm. I have change recently the two muflers with the original MV Corse muflers. Before that i had change the air filter with a DNA one, i had also change the catalytic converter with an arrow pipe and the eprom chip with an MV Corse.
Has anyone any idea why is that happening?
Thanks in advance
 

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Discussion Starter #8
Did you check the coils.
My Brutale 750 has had similar symptoms when only one coil was partially defective.

I am going to try the diagnostic software and see what it says. Thanks for the tip!
 

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I am going to try the diagnostic software and see what it says. Thanks for the tip!
Actually diagnostic software won't be of any help, even testing a coils using multimeter as described in workshop manual (while they are cold) probably won't be of any use, at least it wasn't in my case...
I indentified the fault coil (4th cylinder) by obvious increasing pressure in vacuum line while miss firing, after that i swapped coils on 1st and 4th cylinder and of course increasing pressure now occure on vacuum line attached to intake on 1st cylinder while miss firing.
Before that my (authorised) mechanic spent two days working on bike, diagnostic software didn't show any problems, TPS was set correctly, vacuum balanced ???? after that they changed spark plugs, checked fuel pump, pressure regulator, fuel filter, hoses, even checked injectors (cleaned all and then instaled 2 new) ... ALL THAT FOR NOTHING!!
Btw, I list all above so maybe you'll find somethin useful in my experiance ;)
 

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Discussion Starter #10
It will be helpful to eliminate all the other possibilities and sensor failures I hope. I'll try to locate some coils in the mean time as it seems like we're on the right track.
 

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If it was the TPS the bike wouldn't work properly at all. Not even at the idle speed. It happened to my bike and my(authorised)mechanic changed the TPS. (It is the same with the Ducati Monster and if you buy it from them is much cheaper because MV Agusta does not sell the TPS separatelly from the throttle bodies!) He also believed that the throttle bodies needed vaccum balance(if i am writing it right, 'cause i don't speak that well the english language as you). Al, don't try to found coils! I found 4 used coils on ebay and i bought them! I didn't took the bike yet to the workshop. When the coils arrive, i will change them immediately. If the problem is solved, I will inform you and I will send you one coil. I don't know the price for the a new one but i bought it for 25 euros from Germany(motorrad teile is the name of the shop also take a look at the imperial bikes shop).
 

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Discussion Starter #13
If it was the TPS the bike wouldn't work properly at all. Not even at the idle speed. It happened to my bike and my(authorised)mechanic changed the TPS. (It is the same with the Ducati Monster and if you buy it from them is much cheaper because MV Agusta does not sell the TPS separatelly from the throttle bodies!) He also believed that the throttle bodies needed vaccum balance(if i am writing it right, 'cause i don't speak that well the english language as you). Al, don't try to found coils! I found 4 used coils on ebay and i bought them! I didn't took the bike yet to the workshop. When the coils arrive, i will change them immediately. If the problem is solved, I will inform you and I will send you one coil. I don't know the price for the a new one but i bought it for 25 euros from Germany(motorrad teile is the name of the shop also take a look at the imperial bikes shop).

Cheers! hopefully we'll both have our bikes running again soon.
 

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a complete shot in the dark here.

is your bike a euro 3 version with a lambda sensor?
a failing lambda sensor could certainly
screw up you injection and map.
 

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Discussion Starter #16
Al, p.m. me your adress because the coils arrived today! :)
PM sent! thanks again


a complete shot in the dark here.

is your bike a euro 3 version with a lambda sensor?
a failing lambda sensor could certainly
screw up you injection and map.
it is a MY2006 910S, so running 16M ecu with no lambda sensor. thanks for the suggestion, I am still waiting on the data cables so I can try the sensor check.
 

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Discussion Starter #18
I changed the coils and it didn't have any effect. I can say that the problem is much more pronounced when the engine is hot. Running from cold it almost feels normal, but as soon as it reaches temp it starts misfiring. Right now it seems like the issue is isolated to low throttle positions like neutral cruising or through a sweeping turn. Everything else seems spot on, but it gets worse and worse as it heats up.
 

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I'm sorry to hear that there is no improvement.
Identical symptoms had my (notably deterioration with increasing temperature), which is caused by the coil on only one cylinder.

Can you determine if a misfire occurs always on the same cylinder?
(using vacuum gauges or infrared thermometer)
 

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Discussion Starter #20
I have changed to the harley davidson "equivalent TPS" the problem persists but it is actually rideable now. I'm running out of ideas and I may have to commit a sin against myself and actually pay a shop to look at it. Considering what that might cost I'd probably be better off buying microtec and mapping it out myself.
 
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