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Discussion Starter #1 (Edited)
Background and problem description:
05 SV650 track bike. I started to notice a problem during a race weekend where is felt like it suddenly lost power and seemed like it was only running on one cylinder while under load on the track. It would feel like it lost power then get back to feeling like full power for a few seconds before falling again. When I came into the pits it didn't want to idle. After messing with it for a few min it would idle again. When I took it back out on the track it ran fine for a few laps then had the same problem and wouldn't idol when I cam back into the pits. I swapped several components between this bike and my other SV but kept having similar issues. After that weekend when I got it home it seemed to be running fine at idle and putting around so I took it to run on a dyno to see if it made full power and if I could recreate the problem. It ran fine for several dyno runs and made good power. The next track weekend I took it to it ran fine for the first practice session then had the same issues as before during the second session. I ended up swapping throttle bodies again and it ran ok for the rest of the day so I assumed that was the issue. That was the end of the season last year so I sent the fuel injectors for all of my sets of throttle bodies to get cleaned. Then put everything back together. When I took the bike to the first track weekend this year it ran great for the first 4 laps then had the same problem. Now it continues to have the issue idling where it will seem to dip in RPM randomly once warming up then eventually sputter out. Also of note I took a temp gun to the headers and the front header is at over 400 degrees once the bike is heated up but the rear header doesn't seem to get above about 250 so it kind of makes me think the issue is with the rear cylinder.

Here is a video of what it's doing at idle. It didn't choke all the way out while I was videoing but you can see and here it take a dip in RPM a few times. Also two of the times I went to give it a little rev it hesitated before revving.
 

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Discussion Starter #2
Components that I've swapped between my two bike so far. My second SV has run fine with all of the parts I've swapped between the bikes:
-Throttle bodies
-Coilpacks
-Gas tank and fuel pump
-ECM
-Air box
-Stator cover and stator/flywheel assembly

Other trouble shooting done:
-Checked voltage at idle and when revving. My volt meter shows 14.3 volts when at idle and when revving. Also I don't see a drop in voltage when the motor stutters
-Removed the power commander to eliminate that as a possible cause
-Changed out the entire main wire harness(this was my most recent effort when nothing else had made a difference)

Recent work done to the bike:
Fresh build on the motor: 0.5MM over OEM pistons, 1st gen rods, cam swap, decked heads, valve job. It doesn't seem to me like a motor issue, but wanted to include this to give the full picture. When we ran on the dyno it made 81 hp.

At this point I'm puzzled and don't even know what to try next. The only other thing I can think to try it to swap the motors between my two bike to see if the problem follows the motor, but that seems like a lot of work when it doesn't seem like something that would be a motor issue. Looking for any ideas at this point....
 

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I agree, the problem is not likely mechanical; swapping motors would be a lot of work for small chance of success. Mechanical problems, generally, are not intermittent.

At first glance, the video looks like the problem might be flaky plug cap or bad connection between the cap to high tension wire(s), a fairly common problem on the SV. But if both coil/wire/caps have been replace then can't be that.

Flaky throttle position sensor can cause idle drops like that but if there is a major difference between header temp cyl1 vs cyl2 (major clue), then anything common to both cylinders, (all FI sensors, fuel pump pressure/flow, bike voltage, etc...) should be able to be ruled out.

Hopefully the bike continues to fail hard as shown in the video. Intermittent problem are the absolute worst to trouble shoot. Of course you know that... :cussing: :)

When power cuts in/out is it abrupt or subtle? Abrupt power cut is often electrical. One problem that would fit the symptoms and has been posted a few times is a poor connection on the spade connector(s) at coil wire tabs. You might try see if those are loose or corroded and if so, clean up and crimp down tight.

Really excellent job you have done trying to isolate the problem so far. Videos are a huge help too.
 

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Discussion Starter #4
I agree, the problem is not likely mechanical; swapping motors would be a lot of work for small chance of success. Mechanical problems, generally, are not intermittent.

At first glance, the video looks like the problem might be flaky plug cap or bad connection between the cap to high tension wire(s), a fairly common problem on the SV. But if both coil/wire/caps have been replace then can't be that.

Flaky throttle position sensor can cause idle drops like that but if there is a major difference between header temp cyl1 vs cyl2 (major clue), then anything common to both cylinders, (all FI sensors, fuel pump pressure/flow, bike voltage, etc...) should be able to be ruled out.

Hopefully the bike continues to fail hard as shown in the video. Intermittent problem are the absolute worst to trouble shoot. Of course you know that... :cussing: :)

When power cuts in/out is it abrupt or subtle? Abrupt power cut is often electrical. One problem that would fit the symptoms and has been posted a few times is a poor connection on the spade connector(s) at coil wire tabs. You might try see if those are loose or corroded and if so, clean up and crimp down tight.

Really excellent job you have done trying to isolate the problem so far. Videos are a huge help too.
Thanks for the response. When the power cuts out it is very abrupt, it goes from full power to less than half instantly then comes pack to full instantly.

I was texting with a friend and they gave me a few more ideas of stuff to check that I hadn't thought of yet. I'm going to check the main ground wire since that wasn't part of the wire harness I replaced. Maybe that got pinched when I was putting the motor in.
 

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The ground is common to both cylinders so if the problem is at the rear only then it may not be that. Nevertheless, still a good idea to check.

Abrupt power cut-in/out, especially if one cyl only, is almost always electrical.

If you get to the point where things just don't add up, sometimes it is good to start over, forget everything we think we know, retest. The problems that kick butt the hardest are if wrong assumptions are made or faulty test result. Those make you check everything else before coming back to the real problem.

Good luck, please let us know what you find. You are doing everything right so I am sure you will solve it. Having two bikes to work with is a big help too.
 

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Didn't read any mention of changing plugs. Not the most likely culprit, but you never know. From what you've described I would focus on anything ignition related for the rear cylinder. I don't remember how the coils are triggered on the SV, but that may be something to look into. A good coil is no good if it's not getting the signal to fire.
 

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Hey man i just red thos ive been searching everywhere to try to find help. My 07 sv650s is doin the same thing it sounds just like that. Did you ever find out what it was? I bought a brand new battery bit no help. IV lost a lot of power and it misses sometimes.. Anyways let me know thanks
 

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Hey man i just red thos ive been searching everywhere to try to find help. My 07 sv650s is doin the same thing it sounds just like that. Did you ever find out what it was? I bought a brand new battery bit no help. IV lost a lot of power and it misses sometimes.. Anyways let me know thanks
 

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Discussion Starter #9
I ended up replacing the whole wire harness and the issue went away. Must have been and intermittent short somewhere. Honestly the most frustrating issue I've ever worked though on a bike.
 
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