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Author Topic: Weird mixture / engine problem - tips needed!  (Read 1035 times)


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Weird mixture / engine problem - tips needed!
« on: November 18, 2012, 10:51:15 am »
Hi there,

I have an annoying intermittent fault I am having a hard time tracking down, as is the shop. The bike will sometimes be very hard to start - as in can run a battery flat. Sometimes it fires straight up, similar temperature days, no real difference.
The biggest symptom of the issue is throttling problems, if I give it some oomph while riding in the first 15 or so minutes, the bike can stop responding. The RPM's cut out and the bike will buck. This is an intermittent problem so hard to track. But it can be dangerous as I'm expecting the use of the throttle. The bike acts as if its getting no fuel, or no spark. However it seems to be getting both.
It doesn't seem to happen so much if the engine is hot (after 15 minutes of riding).
However within that first 15 minutes, I can lose use of the throttle, the engine can cut out completely, but most likely it will just stop accelerating and cut out when I put it under load and give it gas. The engine does appear to need to be put under load for the problems to occur.

When it got really bad the bike would not run at all, it would stall out any time I gave it any throttle. Pushed it to the shop, they changed the plug, (it looked lean) it got better.

I have checked the 02 sensor - (could this be the cause?) it wasn't too dirty. I have cleaned with alcohol.
The side stand switch apparently can cause mixture problems. This has been disconnected.
All wiring / ground seems to be good. No fault lights.

Its really annoying as I don't trust the bike right now which is no fun, can anyone point me in any direction to check? :(

« Last Edit: November 18, 2012, 10:53:17 am by TristanB »


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Re: Weird mixture / engine problem - tips needed!
« Reply #1 on: November 18, 2012, 11:49:45 am »
I would be looking for a loose electrical connection, like the sidestand switch which has been one of the bigger bugaboos on the bike. At any rate start checking all the connections and make sure they are secure.
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Ducati Scotty

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Re: Weird mixture / engine problem - tips needed!
« Reply #2 on: November 18, 2012, 12:18:57 pm »
+1.  Though it seems to be connected to accelerating cutting right out like that is almost always electrical.  If it were something else the bike would buck, snort, cough, etc.  If it just dies it's most likely electrical.

In the nacelle just under the keyed ignition switch is a two prong connector that can come undone but stay close enough to make contact, it comes from that switch.  Take a look.  If it's loose zip tie it together.



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Re: Weird mixture / engine problem - tips needed!
« Reply #3 on: November 18, 2012, 01:08:08 pm »
Thanks guys.

The side stand switch is disconnected.

Here is why I don't believe it to be a simple wiring fault.
(I've gone through most of the wiring), but the problem doesn't occur after the bike has run for a long period of time, ie when its hot.
However in the first 15 - 20 min, the bike can buck, and when throttling / accelerating harder the engine will just stop. I can then release the throttle, the engine will stabilize, and if I throttle more gently it will work as normal.
Its such a pain to diagnose because sometimes it won't have the problem at all. Other time it won't run at all.

I'll break down what I know / don't know to see if any has thoughts.

Symptom. Bike can die / not start / buck when putting engine under load. Intermittent problem.
- Doesn't seem to occur after engine is hot (after 20 minutes).
- Occurs most from cold.
- Bike may refuse to start
- Side stand disconnected
- Plug appeared to have been running very lean
- Bike has had a problem running very rich before (heavily sooted plug).
- After changing plug bike runs well(ish) for thirty days, then problem repeats


Mixture related? Can it be a bad o2 sensor?
Fuel pump related? (but why fail when hot).
« Last Edit: November 18, 2012, 02:18:44 pm by TristanB »


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Re: Weird mixture / engine problem - tips needed!
« Reply #4 on: November 18, 2012, 04:33:29 pm »
Bad O2 sensor will not interfere with starting.

The O2 sensor is not even "in the loop" until the sensor and engine have warmed up.

Most likely I'd look at the following inputs to the computer:  TPS, MAP, POWER & GROUND.

TPS & MAP are the primary inputs used to determine engine load.  After the engine warms the O2 sensor provides a correction signal - however - state changes (handfulls of throttle) require a re-read of the basic load table before application of the O2 trim signal.
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Kevin Mahoney

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Re: Weird mixture / engine problem - tips needed!
« Reply #5 on: November 18, 2012, 05:16:54 pm »
Have you checked for any fault codes? Even if the ight is not on please check. Please send me a PM about this so I don't lose track of the thread. Thanks
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Kevin Mahoney
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Re: Weird mixture / engine problem - tips needed!
« Reply #6 on: November 19, 2012, 09:08:26 am »
I would not give the fuel injector a miss. Examine it as well....


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Re: Weird mixture / engine problem - tips needed!
« Reply #7 on: November 19, 2012, 10:51:41 am »
      It sounds like water in the gas. This is a common problem this time of year. You can get water from the tanks at the gas station, or from parking outside, or from condensation. A half empty tank exposes a lot of metal for moisture to condense on. Drain the tank. Remove the pump and drain it. Before reassembling the tank blow it out with compressed air. Then refill from a different gas station and put in a drying agent such as Heet. I had one where I also had to disassemble the fuel lines and remove and clean the injector.
     I had one weird similar problem with the pulse coil. Greg told me to check it. Sure enough, it was covered with metal filings. This disrupted spark. Wiping off the filings fixed it.
     Do the fuel/water thing first. I have had a few issues with that.


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Re: Weird mixture / engine problem - tips needed!
« Reply #8 on: November 24, 2012, 06:56:43 pm »
Hi Guys,

I found a thread with the exact same symptoms


Hesitating / dying on first and second gear exactly
Instant removal of throttle can rescue the situation
bike died a few times

The outcome (after a lot of hunting) was:

Finally got her back from the dealer 2 weeks ago and it seems the issue is solved! They put in a new ecu & injector to no avail. After she died completly they tracked the problem to the negative wire on the coil that was chafed inside the wiring harness. A month at the dealer who pulled most of his hair out over this issue. Wish RE would use a thicker gauge on all their wires and better connections. I've put about 100 miles on her and she is running like she's supposed to. It seems like most riders issues are solved by electrical problems which can be difficult to trace down. Thanks again for all your comments and suggestions. Ride safe!

So I guess time for me, or dealer to look!

Anyone got any tips as to wear I can find these bits?
« Last Edit: November 24, 2012, 07:13:23 pm by TristanB »