Author Topic: Guzzi breva 750 running on one cylinder  (Read 671 times)

Offline georgiezx

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Guzzi breva 750 running on one cylinder
« on: February 13, 2014, 08:17:13 AM »
Hi there I am new to this forum. I am trying to fix a Breva 750 2006 with only 12000km. The bike is running only on left cylinder. I set the valve clearances, bought new spark plugs checked all electrical connection. Battery is new and I have also a fresh gas. The bike was running perfectly last friday 7.2.2014 when I synchronized the throtle bodies. The very  next day it wouldnt start and when it starts then only on left cylinder. I checked the spark - OK , got spray of gas from the injectors - OK. I checked the spark and the right cylinder has a spark as long as the engine is spinning under the power of the starter. When the engine starts on one cylinder I have to keep it running well above the idle and the spark is gone. Please help me sorting out this problem.

Offline Kiwi_Roy

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Re: Guzzi breva 750 running on one cylinder
« Reply #1 on: February 13, 2014, 09:52:02 AM »
Since both injectors and both coils share a common supply I suspect something wrong with the throttle bodies
Check to make sure the linkages are in place and both are opening together

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Offline cloudbase

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Re: Guzzi breva 750 running on one cylinder
« Reply #2 on: February 13, 2014, 12:15:44 PM »
Yep.

Go back and check your work again.  If it ran fine, and then it didn't after you made the adjustments, then that would be the first place I'd look.

Offline sign216

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Re: Guzzi breva 750 running on one cylinder
« Reply #3 on: February 13, 2014, 12:34:20 PM »
Yep.

Go back and check your work again.  If it ran fine, and then it didn't after you made the adjustments, then that would be the first place I'd look.

Yes, it's possible you accidentally bumped a wire loose. 

Reading your description, you're saying that right side has spark when pushing the starter button, but when running on only one cylinder (the left), the right side has no spark.  Is that right?
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Offline Idontwantapickle

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Re: Guzzi breva 750 running on one cylinder
« Reply #4 on: February 13, 2014, 12:48:20 PM »
You may want to swap the spark plugs from one side to the other to see if the plug may be bad. Also you might try pulling the plug wire off just a little on the one not firing while the engine is running. The increased gap causes the coil to spark hotter and can get a fouled plug going again. As others have noted it is a good idea to go back over what you worked on the make sure it is all OK. You wouldn't be the first of us to make it worse instead of better!
Good Luck.
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Offline sign216

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Re: Guzzi breva 750 running on one cylinder
« Reply #5 on: February 13, 2014, 01:09:32 PM »
You may want to swap the spark plugs from one side to the other to see if the plug may be bad. Also you might try pulling the plug wire off just a little on the one not firing while the engine is running. The increased gap causes the coil to spark hotter and can get a fouled plug going again. As others have noted it is a good idea to go back over what you worked on the make sure it is all OK. You wouldn't be the first of us to make it worse instead of better!
Good Luck.
Hunter

Use caution with the above.  The electronic ignition can be damaged if the spark can't go to ground.  I.e. if you pull the plug wire off too far. 
At least that's my understanding.
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Offline georgiezx

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Re: Guzzi breva 750 running on one cylinder
« Reply #6 on: February 13, 2014, 01:44:59 PM »
Hi I just got back from garage. I swaped the coils, engine hesitated but eventualy started (wouldnt idle) running on both cylinders. After about 3 minutes it died again but was very hard to restart. And didnt run right. It was like the cylinders were running left then right and again. Like I wrote in first post the left cylinder has a spark as long as the engine is spinning with starter but once the engine start running on right cylinder the spark on the left cylinder dissapears. Any hints? I checked the sensor just ahead of the right cylinder, it has 632 ohms. Is that OK? I synchronised the throtle bodies on friday and the bike after was running perfectly, but wouldnt start saturday morning. I was suspecting moisture somewhere in wiring. Spark plugs are new, spark plus caps are new, gas is new, checked the coils they have similar readings. When the bike was running earlier I saw that the speedometer is moving even though the bike is not moving. sometimes the dashboard does not come on but the bike can be started. Guzzi was involved in small fender bender in May nothing serious and then it sat until now.
« Last Edit: February 13, 2014, 01:56:20 PM by georgiezx »

Offline guzzisteve

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Re: Guzzi breva 750 running on one cylinder
« Reply #7 on: February 13, 2014, 02:10:52 PM »
OK, I would start checking the dashboard connection, ignition switch connections, and plugs on the wiring loom, also relays. It may have jarred something loose.

AND Welcome to the forum!!
« Last Edit: February 13, 2014, 03:18:59 PM by guzzisteve »
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Offline Kiwi_Roy

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Re: Guzzi breva 750 running on one cylinder
« Reply #8 on: February 13, 2014, 04:25:38 PM »
 When the bike was running earlier I saw that the speedometer is moving even though the bike is not moving. sometimes the dashboard does not come on but the bike can be started. Guzzi was involved in small fender bender in May nothing serious and then it sat until now.

From this symptom I suspect there is a loose connection somewhere making the dash or ECU think it's getting speed pulses e.g. a loose positive or ground. Another thing I would suspect is the ignition switch, try flicking it numerous times, perhaps with the main fuses out, this might be enough to clean the contacts a bit to get a better contact. If it does improve then pull the switch apart and clean.
Check grounds around the ECU and dash. It could also be a dirty kill switch and perhaps the side-stand switch.
If you have a multimeter check the voltage at the top 2 fuses on the diagram, it should be steady 0 with switch off + 12 with the switch closed.

Needless to say disconnect the battery cables and clean the terminals, check the main ground
It's Electrickery for sure ;D

Good Luck
« Last Edit: February 13, 2014, 04:37:30 PM by Kiwi_Roy »
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Online Vasco DG

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Re: Guzzi breva 750 running on one cylinder
« Reply #9 on: February 14, 2014, 12:15:36 AM »
You say you balanced the TB's? How did you go about this? Did you adjust the idle speed? If so how?

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