High speed, low throttle stumble/power dip

Its for problems like this that a dyno is a wonderful tool.

Pete

My son loves dynos! His favorite is the Ankylosaurus!

; )

Man, if only there was a motorcycle shop that had one around here...along with a smart tech. I'd be there asap.

I've been helping a guy with a Breva 750 who has a similar problem. He found one of his injectors had a connector contact that was barely touching the pin on the socket causing intermittent connectivity. Check 'em.


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beetle wrote:

I've been helping a guy with a Breva 750 who has a similar problem. He found one of his injectors had a connector contact that was barely touching the pin on the socket causing intermittent connectivity. Check 'em.
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Was one of my first stops, even wiggled and checked the wire in the connectors. Any chance the injectors are severely clogged? I know these are the showerhead nozzles (many spray jets), not single spray jet. Can they be disassembled? or taken off and power cleaned? It does feel like it is a lean condition, and it will be interesting to see what happens with the new fuel pump/filter.

I need to pull the tank to find the Tom Tom Power lead for my USB power outlet, so I will pull the ECU connector, check the ground, etc and reconnect.

Now on the issue of a dyno, what is keeping me from throwing my laptop in my top box, leave it connected to guzzi diag and go for a ride? Does it have the capability to record while riding? I'll leave it connected, wrap the laptop in a towel and go for a quick ride.

I'm gonna fix this damn thing..... It is an Air Cooled V Twin but it ain't a Harley and should not have a 6000 redline...... lol

I'm about at a stop. Hopefully MI can get to the solution. There are three mechanical things left to check, a clogged Cat (no idea how to do that other than replace it), partially clogged injectors, or a problem with fuel delivery from pump/clogged fuel filter/weak pump. I think both of those are unlikely with under 3500 miles. Will be interesting to see what happens when they swap out the pump/fuel level sender & filter.

Could it be the crank sensor that sends bad signal at high RPM? any other sensors to mess with the fueling at high RPM? It's just odd to me that at 6000 RPM in any gear that this happens. Load, and fuel fuel demand is different in 1st than it is in 4th, but it reacts the same in any gear at the same RPM. If it was a fuel flow issue, I think I could trigger the issue at varying RPMs but it is at a constant spot.

Re flashed Map, used another stock map and a Beetle Map, all basically the same. Valves are right, TB's are balanced, checked all connections, pulled the fuel injectors, blew them out with carb cleaner, reconnected. Also did a canisterectomy, reset parameters, set TPS, all is tight, good connections, and below 6K this thing is running SWEET.........Solid idle, smooth engagement of throttle and response, But hit 6000 - 6500 + and it falls on its face.

I hooked up Guzzi Diag, put the laptop in the top case figuring I could take it for a ride and see how things changed, but discovered it doesnt have a logging feature... lol. Oh well....

I also in removing the tank discovered that the allen bolt was stripped and stuck in the tank.......... No fun to get out. Also found the threads on the right injector were buggered up in the head. Diddnt effect the seating and tightening but was cross threaded on install, so maybe Luigi was a bit soused when he assembled the right side.......... lol. I also noticed that the airbox oil drain line was full of oil.

Bulldog - fyi GD certainly has logging. Go to File then Preferences. Dialog box comes up.
Choose Extras tab and click on the last check box. Don't have laptop with me but think the log gets saved as .csv in a logfile folder in wherever you have GD installed.
Conor

Your logic is sound, but it it still could be an injector. Might be a frequency thing. I doubt it's the fuel pump or related. Might be the the phase sensor, but I would think that you'd get problems at other RPM's as well. It would be worth checking the shims are right.

Would be worth logging with GD, but if it's a mechanical issue, the data won't tell you.


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I've done similar, Bulldog. Also just cleaned out injectors and checked conections. I've run out of easy stuff that I'm comfortable checking.

A few notable additions: The right side plug quickly shows signs of fouling, like within 50 miles a brand new plug gets a sooty black tip.

Also, If I adjust the CO trim to like -50 it changes the behavior somewhat. I'm just messing around with anything I can adjust at this point, so not looking for anything in particular. What happens is that it will surge abruptly instead of just totally going flat. So before it would just lose power at around 5500-6000 rpm almost like a switch -- like Bulldog mentioned previously. Now it'll act like it wants to work, then go flat, etc etc.

Putting CO trim back to 0 it just goes flat, especially with progressive light throttle. Going full throttle will sometimes acts like it wants to go, especially if I give it a running start so to speak. If I lightly throttle up to 5500 or so it just goes blaaaahhh. If I then cracked it wide open from there it'll buck, surge, and go blaaahhh.

I'm a bit broke and a long way from mechanic, so will keep watching for your updates Bulldog (and any others).

Just bought a multimeter, so maybe I'll check the coils just for giggles.

This seems sorta related: [You must be registered and logged in to see this link.]

That's a post from the previous owner. I emailed him and he didn't experience anything other than what he explained in his thread. Maybe that was the start of something that got worse over time? Just a coincidence?

Reading that thread, looks like he fixed it with a map. I wonder what changed for you now? How many miles are on your bike?

I havent messed with the CO trim, other than checking it was at 0.

I'd like to pull the plugs to check but they "upgraded" to the NGK caps and I have to pull the bodywork (a Norge 8V) to pop up the caps. I need to do some kind of double zip tie contraption to pull them up, cant do it by the wires, and tube is too tight. NOT liking that upgrade, but the stock boots do cause a problem so.....

I agree with Beetle, it is likely not the fuel pump or filter, that is being changed because of the fuel gauge sender issue, so that is where they will start. I'm not optimistic to tell the truth, and while a 6K redline is very rideable, its less satisfying than I'd like. Seems a rare 8V issue with no fixes thus far.

I've reached out to the PO of my bike to no result. Looks like he was a 'botique' dress up rider, owned it for a few months rode it without the bags, dropped it and traded it on a sportster 1200 with cute little hard bags....... Yes, I facebook stalked him..... I'm thinking that mine never ran right and it runs so good up to the drop off and has decent power I can imaging the 1500 miles he put on it he never really explored. I on the other hand like to run to redline, and do so responsibly on every ride, with the occasional bump off the rev limiter......

I'm going to do the guzzi diag and log, no idea what it will look like or how to read it, but I'm hoping to see something show on the timing or fueling. Will also be interesting to see.

MotoMT wrote:

I've done similar, Bulldog. Also just cleaned out injectors and checked conections. I've run out of easy stuff that I'm comfortable checking.

A few notable additions: The right side plug quickly shows signs of fouling, like within 50 miles a brand new plug gets a sooty black tip.

Also, If I adjust the CO trim to like -50 it changes the behavior somewhat. I'm just messing around with anything I can adjust at this point, so not looking for anything in particular. What happens is that it will surge abruptly instead of just totally going flat. So before it would just lose power at around 5500-6000 rpm almost like a switch -- like Bulldog mentioned previously. Now it'll act like it wants to work, then go flat, etc etc.

Putting CO trim back to 0 it just goes flat, especially with progressive light throttle. Going full throttle will sometimes acts like it  wants to go, especially if I give it a running start so to speak. If I lightly throttle up to 5500 or so it just goes blaaaahhh. If I then cracked it wide open from there it'll buck, surge, and go blaaahhh.

I'm a bit broke and a long way from mechanic, so will keep watching for your updates Bulldog (and any others).

Just bought a multimeter, so maybe I'll check the coils just for giggles.

This seems sorta related: [You must be registered and logged in to see this link.]

That's a post from the previous owner. I emailed him and he didn't experience anything other than what he explained in his thread. Maybe that was the start of something that got worse over time? Just a coincidence?

Hi
Can I have an idea

MotoMT wrote:

Hey all. New owner here who is a bit stuck. Hoping to get insight.

I recently purchased a 2015 GRiSO which came with a Mistral carbon high pipe.

The bike runs great up to about 5500 RPM where it abruptly just, well, doesn’t go. It’s disconcerting especially at highway speeds. It just loses power. The exhaust note makes an audible dip in tone as well. This is at low to mid throttle. If I open it up, then I can blast through, but it will still sputter a bit before going like a rocket. It makes the bike entirely unrideable except around town.
Took another ride last night. The bike will not go past around 7500 rpm. Giving it full throttle makes it almost impossible to ride above 5500 rpm. It'll run for a second with power then immediately drop to no power back to power, bucking the whole time.

A few notable additions: The right side plug quickly shows signs of fouling, like within 50 miles a brand new plug gets a sooty black tip
?

Hello.
I guess the problem is present since you motorcycle.

I know if 2 or dsitribution was shifted a tooth on the top sprocket.
This makes the engine climbs in the towers juqu'à about 5000rpm then it's hard to reach 7000 rpm.
Lack of power after 5000 rpm.
The engine can not go up to 8500 rpm.

timing control high pinion.
Possible problem side Right distribution.
Position spot Valves close, rockers free PMH

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Control side left

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Bike has 3900 miles on it. How plausible is Jean's idea? Is that something that could happen from factory, or something else? Worth checking?

Sorry if dumb question : /

Super frustrated and way past my comfort zone on this : (

Hi mate, while I am not anywhere near as useful as Pete or Mark in problem solving this, I can tell you that the surging you described was a symptom of an arcing lead that my bike suffered early on. In my case the oil was escaping the o ring and filling the plug tube. A blocked drain meant that the oil eventually shorted the plug to the engine.

I reckon that is why Pete keeps going to the leads it sounds just like it.

In saying that, the rev issue that is dependant on throttle position sound so much like a fuel issue. I wish you luck, makes me really appreciate having access to gurus like Pete, even with a tractor like the MG I would be lost.

Checking the cam timing is easy enough. I doubt it's the issue but it's certainly worth checking.

Pete

Hello.

Yes, it would be surprising mileage, although I have seen on other models GRiSO or sport forum with AAC problems 6000 km.

Should know the history of mechanical interventions and reminders?

Can be bad idea to me.
Sorry

I had a distant cousin, John, from my Greek side (he passed some years back), who was quite the tinkerer, and could fix seemingly anything. He had bought a Citroen SM for a song back in the mid-seventies, because the thing ran like crap, and no one, including the dealership, could figure out why. Even factory mechanics flew out from France to see if they couldn't get to the bottom of it, still to no avail (how do you say "WTF" in French, pardon my, er, French!). The SM came with a Maserati 3 liter V-6, same engine as what powered the Merak, I believe. So John decides to check the the cam timing, casting aside the assumption that everything that comes from the factory is manufactured/assembled to spec. It turns out that one of the cam shafts, each which has a small index mark on the drive sprocket for setting the cam timing, was incorrectly indexed. So he set the cams 'incorrectly' (if you were to use the shop manual as reference), and it ran like a champ thereafter.

My thought, though, is that if the issue here were an improperly indexed cam, wouldn't it run poorly from idle up? In any case, my cousin's story aside, personal experience has taught me that being off by even just one tooth can make a huge difference in how the engine performs (don't ask me how I know this, but that's another story).

ronbo10 wrote:

My thought, though, is that if the issue here were an improperly indexed cam, wouldn't it run poorly from idle up? .

Hello.

Nice story!.
Yes idle may be correct, with different engine noise.
I found on the web 1 sport and 1 stelvio  with improperly indexed cam.
But the engine tops out at 5500 rpm with difficulty to go to 7000 rpm.
The mechanic realized the problem by comparing with another motorcycle  

I quote
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"J'ai trouvé la bécane bruyante et avec un son que je ne reconnaissais pas.,J'ai donc fais 150 bornes en restant sous les 5000 tours. Puis j'ai voulu ouvrir un peu, et là... rien ! Au delà de 5000 plus de watt, la bécane monte péniblement dans les tours sans jamais atteindre les 7000.
avoir cherché 2 jours il s'aperçoivent que la distri était "décalée d'une dent". "


That said, it is difficult to say anything.
Even when members of a forum speak the same language origin, there are understandings errors.
Then !

As I said, worth checking. The 8V isn't a collision motor at one tooth.

Probably easier to do a compression test. The figures go really weird, (Like 260PSI!) if it's a tooth out one way...

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All this shit is fixable Steve. It's just a matter of working out which shit is *The* shit! Hard to do with the internets and no hands on with the machine.

I'm cooler than a frozen turd sandwich!

Many years ago (when men were men & bikes didn't carry computers for brains etc) your symptoms fit perfectly with ignition HT/coils/plugs breaking down under heavy load. I had two bikes that had this type of issue - first was a two stroke that started doing exactly what you described when spark plugs eroded down enough to cause major pinking at high revs (usually after just 3000 miles from new plugs - man it ate plugs); and second was Z650 B that had well known coil breakdown issues that limited revs....For the Z650 I lived with it for ages as it just acted like a lower level rev limiter and I couldn't afford new coils. Just a thought but HT/coil/ignition problems fit pretty well with sooty (& sweep) plugs as well......today obviously a lot of other factors & sensors can scramble ignition....not sure it helps but I'd be starting on ignition angle before fueling if it was me..BTW in old days carbon build up in head could also cause power issues but with so few miles I can't see that can apply here.

Interesting discussion. Unlikely a cam chain is my issue, which I am more convinced than ever is a fueling issue, but we will see. BIke is running excellent right now, and completely dialed in until it falls on its face. Am about to go burn off some rubber and hydrocarbons over the long weekend..... Here is Day 1. I leave tomorrow AM. CAIO

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Steve,

A long day, but a goodie. The Black Ball ferry from Port Angeles to Victoria is a fun crossing. With any luck you'll see some orcas. Take lots of pictures!

Pete

Converted Duc wrote:

Hi mate, while I am not anywhere near as useful as Pete or Mark in problem solving this, I can tell you that the surging you described was a symptom of an arcing lead that my bike suffered early on. In my case the oil was escaping the o ring and filling the plug tube. A blocked drain meant that the oil eventually shorted the plug to the engine.

I reckon that is why Pete keeps going to the leads it sounds just like it.

In saying that, the rev issue that is dependant on throttle position sound so much like a fuel issue. I wish you luck, makes me really appreciate having access to gurus like Pete, even with a tractor like the MG I would be lost.

Appreciate the encouragement

From what little I understand, I figured that changing the plug caps (SBO5E), plugs, and new leads would be a good guess at a fix. When that didn't work, I realized it was a bit more than just the basics.

Your comment, paulbrice, is exactly what I was thinking. I'm not a mechanic by far, but I've farted around enough with bikes and cars where I thought that ignition related stuff is the first to check.

I'm gonna check coil resistances this weekend, maybe one has gotten all wonky. Except if the ecu hasn't registered any error codes for the coils (or injectors lets say) then is it still worth checking? Nothing shows up in GuzziDiag when checking for errors. I was looking at the code list in the service manual out of curiosity. It sure would be much easier if something was showing up ; )

Thanks for the discussion all. And ride safely, Bulldog!

Hello

I agree on the fact that ignition problem is most likely on the motorcycle MotoMT.
Since the spark plug cap seems harmless, it's time to test the HT coil right.
But a test of resistance may not be revealing. (Random)
If possible, it is better to make a standard exchange with another reel that works.
It is more demonstrative.

A bientôt.

Pete Roper wrote:

All this shit is fixable Steve. It's just a matter of working out which shit is *The* shit! Hard to do with the internets and no hands on with the machine.

I'm cooler than a frozen turd sandwich!

Pete, I was not refereeing. Sorry for the confusion. I was just musing on the Jean Cool moniker. Too bad there wasn't a bereted Snoopy to be found...