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Discussion Starter · #1 ·
My bike has recently started exhibiting a strange power loss. Occasionally when I'm out riding, the power will suddenly and noticeably drop, I'll need to use more throttle to maintain the current speed, rpms will be limited to about 7-8k at WOT, acceleration will be severely limited, and the bike will die at idle. Usually the bike will "snap" back into normal power and throttle response after a while, and thumbing off the killswitch and restarting have worked the couple of times I've tried it.

The patient is a 2002 748 Biposto, which I believe has the 1.6 ECU, and an Eprom chip.

I'm thinking the TPS is starting to go bad or perhaps has gone out of adjustment? I plan on going over it according to my Desmo Times and Haynes manuals this week. I don't have the MDST software, so I'll be limited to diagnosing with a multimeter. Any tips on testing the TPS? Or is there another potential cause I should be looking into? Thanks in advance for any help.
 

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Old Wizard
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Sounds like you're dropping out one cylinder. Check your plugs.

If it's not ignition then it's fuel. Check for a split fuel line inside the tank or a plugged fuel filter.
 

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one word

Seafoam. Use double the recommended dosage and one tank of gas will do the trick.
 

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Discussion Starter · #5 ·
Both plugs look good, but I will try to hop off the bike and feel for hot gas coming out of both exhaust pipes next time this happens.

I put some Seafoam in, and plan on riding through a tank once the weather improves (3 straight days of rain according to the forecast :()

And I'll check the fuel filter and lines next time I take the tank off, before fumbling with the TPS. Thanks for all of the suggestions.
 

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If it's dying when the bike heats up (180-190 degrees), then it could be the same thing that happened to mine. I'd be out for a ride, and once the bike really started to heat up, it'd lose power just like you're describing. I thought it was a fueling issue, and checked everything. After about 2 weeks of scratching my head, I went to the professionals. The DucShop replaced a relay that (and I don't know exactly what it does) has something to do with the throttle bodies. The relay is mounted under the tank, towards the front left hand side. You can see it without taking the tank off, but you'll have to take it off to replace the relay. It sits on top of the coolant resevoir to the left of the key. Mark at the DucShop said that this is a common component to fail. As the bike heats up, the bad relay's electrical connections foul up and voila: massive powerloss. Check that relay out (or have someone check it out for you). My guess is that's the issue right there.
 

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Discussion Starter · #7 ·
Very interesting, thanks for that. I haven't correlated the power loss to the temperature that the bike was running at, but I'll keep an eye on it next time I ride.

If it's dying when the bike heats up (180-190 degrees), then it could be the same thing that happened to mine. I'd be out for a ride, and once the bike really started to heat up, it'd lose power just like you're describing. I thought it was a fueling issue, and checked everything. After about 2 weeks of scratching my head, I went to the professionals. The DucShop replaced a relay that (and I don't know exactly what it does) has something to do with the throttle bodies. The relay is mounted under the tank, towards the front left hand side. You can see it without taking the tank off, but you'll have to take it off to replace the relay. It sits on top of the coolant resevoir to the left of the key. Mark at the DucShop said that this is a common component to fail. As the bike heats up, the bad relay's electrical connections foul up and voila: massive powerloss. Check that relay out (or have someone check it out for you). My guess is that's the issue right there.
 

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If you pull the cap off when the bike is running and it lookslike a whirlpool in there, you may have a broken fuel line.

-M
 

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Discussion Starter · #9 ·
As an update, the bike was indeed running on one cylinder. Checking all the fuel hoses, fuel filter, and replacing the spark plugs made no change. In fact, it seemed to have gotten worse in that the bike started up with low power and didn't "snap" back to normal as it had before. I did a quick sanity check on the spark plug leads: started the bike, pulled the vertical lead--no change, still running on low power; pulled the horizontal lead--stalled engine. Aha! Somehow my vertical cylinder had quit on me. So I followed the spark plug lead up, hoping to find something obvious, and bingo, the wiring connector to the vertical coil had worked itself loose. That would explain why the bike was losing power only intermittently at first, and progressively getting worse as the connector got looser. I love the easy fixes! Really glad I didn't start fiddling with the TPS too!
 
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