Breva 750 'hickups'

[Holt]

Dawnrader wrote:

I'm having exactly the same issues with my Breva too...

From a cold start she idles poorly (purr-purr-coff-purr) then after around 3 minutes she totally dies with a coff or a pop. Not very tech sounding i know but it's driving me crazy. I'm now starting her and waiting for her to die before restarting and trying again. It only ever happens the once but when at lights she some times dies a little and if i pull the clutch in to the bar she goes again.

I have noticed that when filling my petrol tank up there is excess water running into my fuel tank, i've discovered the drain hole is blocked and will be fixing that the first second i can. I stuck some Red-Ex (uk injection cleaner) in it and she ran fine, im just wondering if my water in the tank is causing my rough riding?

Any suggestions?

Nic
x

If you got water into the tank, add (some more - you already got 5%) ethanol to the gasoline. The ethanol will solve the water into the gasoline/ethanol mixture.
It's an old solution used up here wintertime back when this was a problem, i.e. the merry times before pre-mixed ethanol and EFI's.

 

[Eric]

Lori and I have been at this problem for a very long time on her lil Breva. It has 16,000 miles on it now and it has never been a consistent runner. This problem seems to crop up most every ride. Each time we solve it she says "I'll believe it after 600 miles" and it always happens again. Here's what we've done.

1. All the usual: valves, balance, etc.
2. replace fuel filter, air filter
3. Remove charcoal cannister and re-route the hoses thinking there might be an air leak in the mile and a half of rubber someplace
4. Unplug the drain hose for the fuel tank. Yes it was plugged and had to be drilled out.We actually thought that this solved it but, 900 miles later, it was back.
5. Checked all the rubber for air leaks
6. Reset the TPS over and over again

It's an infuriating problem because it will run like a dream for a while after every effort and then it returns. Our latest thought has to do with the TPS. The last time we hooked up the VDSTS, turned on the key (didn't start the bike) and connected, the TPS read 2.7. After starting the bike, it read 3.1. The same thing happened another time but it read 4.0 until we started the bike. Could it be an intermittent failure?

 

[Holt]

Eric wrote:

Lori and I have been at this problem for a very long time on her lil Breva. It has 16,000 miles on it now and it has never been a consistent runner. This problem seems to crop up most every ride. Each time we solve it she says "I'll believe it after 600 miles" and it always happens again. Here's what we've done.

1. All the usual: valves, balance, etc.
2. replace fuel filter, air filter
3. Remove charcoal cannister and re-route the hoses thinking there might be an air leak in the mile and a half of rubber someplace
4. Unplug the drain hose for the fuel tank. Yes it was plugged and had to be drilled out.We actually thought that this solved it but, 900 miles later, it was back.
5. Checked all the rubber for air leaks
6. Reset the TPS over and over again

It's an infuriating problem because it will run like a dream for a while after every effort and then it returns. Our latest thought has to do with the TPS. The last time we hooked up the VDSTS, turned on the key (didn't start the bike) and connected, the TPS read 2.7. After starting the bike, it read 3.1. The same thing happened another time but it read 4.0 until we started the bike. Could it be an intermittent failure?

It's a shot, but, how's the battery voltage & output? Can you masure 13,something volts over the battery, when the motor is running, headlight on (yeah, it turns on automatically, but some people disengage that function) etc ?

 

[NOLAGuzzi]

Eric wrote:

The last time we hooked up the VDSTS, turned on the key (didn't start the bike) and connected, the TPS read 2.7. After starting the bike, it read 3.1. The same thing happened another time but it read 4.0 until we started the bike. Could it be an intermittent failure?

Are you looking at the alfaline_0 channel in the software or the falsely labeled TPS status bar? The TPS position is displayed in the alfaline_0 channel.

 

[Eric]

Yes, 13 volts. As a matter of fact, what was one of our earlier thoughts. We replaced the battery and it ran beautifully for a while... and then it came back. Thanks for the tip of the TPS channel. We're using the right channel thanks to this site.

 

[RJVB]

Have you seen the discussion about the effect of bad spark plugs in the "Here we go again" thread? Can that be ruled out here?

 

[Eric]

Yes. Several sets of new sparkplugs have gone in along with new wires. It seems to be a problem that comes up from time to time with more than a few of these bikes as the French board suggests. We went out to the Black Hills last summer and it was so bad we thought we'd have to park it but once it was out there it ran flawlessly for more than a week riding every day. Back home it started causing problems again. Yes, we thought it might be bad gasoline but it happens too often and in too many places for it to be bad gas. What I'd like to do is buy a salvage 750 breva and start swapping out parts: coils, computer, whatever it takes. But I can't help but think this is a bigger problem that affects more than a few bikes - like the hydraulic valve bikes. Maybe only a third were affected but it was a systemic problem.

 

[john zibell]

Eric,

I'm suspecting a problem with the TPS. Even if you look at the wrong channel, it should be consistent. The TPS is just a variable resistor and may be giving spurious readings. I suggest replacing the TPS as a start and go from there.

 

[Eric]

Ok. I took it out for a spin as soon as I got home. It ran terribly. I put it on the VDSTS and the alphaline_0 channel read 4.0 - it should be 3.1. I reset it and it still reads 4.0 (turn on the bike when it tells me to and wait 15 seconds). I tried again and it still reads 4.0

What does this mean?

 

[john zibell]

Eric wrote:

Ok. I took it out for a spin as soon as I got home. It ran terribly. I put it on the VDSTS and the alphaline_0 channel read 4.0 - it should be 3.1. I reset it and it still reads 4.0 (turn on the bike when it tells me to and wait 15 seconds). I tried again and it still reads 4.0

What does this mean?

The manual states that if the TPS fails to reset, replace the ECU. I hope you are still under warranty. If not under warranty, I'd try replacing the TPS first and hope to get lucky.

 

[Holt]

John;

You knowledge about these electronic gadgets are invaluable to me!!
Thanks;


Anders

 

[RJVB]

Is there any other way to check the TPS, like with a voltmeter, as it is done on the V11 and earlier? I presume that if the VDSTS reading is supposed to read 3.1, you'd also read 3.1 when measuring the voltage across the variable resistance. In any case, it shouldn't be wildly different, and it should vary nicely with throttle position.

However, from what I understand, the reset procedure just alters a reference variable stored in the ECU, basically telling the ECU that this voltage is your "zero". If that procedure doesn't work, I fear it most likely means something on the ECU is toast (or the TPS reading is completely off the acceptable scale, but then I guess the bike just would hardly run at all?)

 

[NOLAGuzzi]

Holt wrote:

John;

You knowledge about these electronic gadgets are invaluable to me!!
Thanks;


Anders

+1
Invaluable indeed.

 

[NOLAGuzzi]

RJVB wrote:

Is there any other way to check the TPS, like with a voltmeter, as it is done on the V11 and earlier? I presume that if the VDSTS reading is supposed to read 3.1, you'd also read 3.1 when measuring the voltage across the variable resistance. In any case, it shouldn't be wildly different, and it should vary nicely with throttle position.

However, from what I understand, the reset procedure just alters a reference variable stored in the ECU, basically telling the ECU that this voltage is your "zero". If that procedure doesn't work, I fear it most likely means something on the ECU is toast (or the TPS reading is completely off the acceptable scale, but then I guess the bike just would hardly run at all?)

I am pretty sure the units are degrees so a volt meter won't tell you much.

 

[NOLAGuzzi]

Eric wrote:

What I'd like to do is buy a salvage 750 breva and start swapping out parts: coils, computer,

for your consideration, there is a breva being parted out on ebay right now. there is an ecu and at least one coil.
I tired to post the link but it comes up blank. Just type moto guzzi breva 750 in the search and look in the ebay stores. I hope you find the answer.

 

[RJVB]

Hmm, not anything in direct terms, no ... although some helpful soul could make an equivalence table on a bike that's known to be tuned properly and running right

 

[NOLAGuzzi]

Ahh, interesting.

So in theory I could hook up my vdsts software and record the parameters for tps position and voltage then plot them and get a straight line. Then use a regression analysis (my high school math teacher would be so proud) to use one parameter to predict the other?

I think you can log data in the software so that would be an easy thing to do. I will give it a try, but I am not sure my breva would be a good standard. Proof of principle would be nice though.

Thanks for that idea.

 

[john zibell]

RJVB wrote:

However, from what I understand, the reset procedure just alters a reference variable stored in the ECU, basically telling the ECU that this voltage is your "zero". If that procedure doesn't work, I fear it most likely means something on the ECU is toast (or the TPS reading is completely off the acceptable scale, but then I guess the bike just would hardly run at all?)

Correct.

 

[john zibell]

NOLAGuzzi wrote:

RJVB wrote:

Is there any other way to check the TPS, like with a voltmeter, as it is done on the V11 and earlier? I presume that if the VDSTS reading is supposed to read 3.1, you'd also read 3.1 when measuring the voltage across the variable resistance. In any case, it shouldn't be wildly different, and it should vary nicely with throttle position.

However, from what I understand, the reset procedure just alters a reference variable stored in the ECU, basically telling the ECU that this voltage is your "zero". If that procedure doesn't work, I fear it most likely means something on the ECU is toast (or the TPS reading is completely off the acceptable scale, but then I guess the bike just would hardly run at all?)

I am pretty sure the units are degrees so a volt meter won't tell you much.

Actually the readings are in millivolts. The ECU/VDSTS/Axone/navagator convert the voltage reading to degrees.

 

[RJVB]

Yes, you could even add an independent measure of throttle opening, and associate that with voltage measured at the TPS, and the value (angle) shown in the VDSTS. You'd indeed expect to find a straight line (with your and the ECU's measure of throttle opening coinciding), but there is no hard reason why that relationship ought to be linear. It could already reflect the amount of air that can pass the intakes as a function of throttle opening, I'm not sure how that function would look (the throttle controls the diameter of the opening, airflow would be proportional to the opening's surface, so there'd be a square in there somewhere?)

In any case, it'd be very interesting to have the relationship because of the ECU behaviour's potential dependency on voltage as described above. Imagine, the ECU gets information about the throttle opening through the TPS, physically based on a voltage across a potentiometer that is generated by a current that passes through that resistance. This circuit is part of the bike's bigger electrical circuit, which is fed from the alternator, which depends on the running engine but which feeds other things that can draw current too. In short, voltage across the TPS is not perfectly independent from the running engine, the very thing it is supposed to control. This may lead to oscillations, and that might just be what we're talking about here.

Am I over-analysing again?