High speed, low throttle stumble/power dip

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.

I asked the previous owner if he had similar issues, and if he had a new map to go with the pipe. He said on a different pipe and map that he did, but had the Mistral sorted out. This is the map he said was on the bike: Griso24S-FU2-Mistral-NodBK-5124.2014.10.02.bin, but that’s for a flat tappet bike, yeah?

I purchased a new Beetle map from GRiSO.org, because I want to run with the decibel killer in. This is the map I purchased: Griso24S-FU2-R-Mistral-dBk-4E1.2015.12.29.bin, which I believe to be correct?

The map uploaded properly using IAW Writer.

Some things I’ve checked:
- Right side spark plug was carboned up badly, so I just went ahead and replaced spark plugs.
- Checked all electrical connections to make sure they are connected/tight.
- Pulled gas tank and checked all vacuum lines and fuel lines.
- Checked airbox. Cleaner is good, and box is clean.
- NGK plug wire caps
- TPS reset

For tuning everything checks out:
- .1 and .15 on valve clearances.
- Brand new spark plugs
- Check TB balance with my fancy CarbMate TS-111. They are in balance at 4,000 rpm.
- Bike was recently tuned, so I didn’t expect anything out of whack. But it was good to check.

I've read though this and the other popular Guzzi forums. At this point I don’t know what to do. I’m chalking it up to user error and I can’t see something right in front of me. It does the same thing with different maps, although taking the db killer out makes it run slightly better. An ideas? Injectors bad maybe? (please say no, lol)

Also related: I was hoping to go back to stock since I fear the Mistral will be too loud on longer rides. Problem is I have no way of doing that currently, is that right? Is there a way for me to get a factory stock map?

Something definitely amiss but what? Dunno? Sounds like a pipe blockage of some sort but unless you've got Japanese market headers this would seem unlikely.

Check the plug caps aren't arcing.

Pete

Thanks for the reply, Pete! Not to get all sappy, but thanks for being such a great resource for the Guzzi community. You're kinda internet famous; )

I had the oem caps originally when trying to figure this out. Replaced with NGK when I put in new plugs : /
Will check again, since I never checked NGK ones after I installed.

Would missing exhaust header/manifold gaskets cause this type of problem? Cause I don't have 'em

Got bored after work. Since you mentioned blockage, figured it's easy enough to pull everything off an have a look. Left side, inside nut was finger loose and both sides are missing the gasket -- part no. 976376.

MotoMT wrote:

Would missing exhaust header/manifold gaskets cause this type of problem? Cause I don't have 'em

Er..yeah!  

Not sure why I didn't check that first, haha. Was so focused on the tune and pipe I kinda got blind to anything else. Hope this fixes it. Will update when I get the gaskets in mail next week. So...any damage done? It's been without those gaskets for who knows how long. Few hundred miles at least : (

I've got the same issue with my Norge, running stock can and map (2200 miles), but same basic issue but the bike doesnt recover, it just stays flat.. Bike has a proper valve adjust, balance, and new plugs/ caps and some fuel cleaner has helped,  but not fixed. The flat spot comes on at 6000-6500 and feels like fuel starvation to me or maybe 1 cyl drops out but that wouldnt make sense. Is almost like a switch. Pulls hard at WOT untill 6K & then flat.  I have it going in for a new fuel pump/sender due to fuel level, which may or may not fix.  Do you have the stock can and can you go back to stock to see if it runs right?

A few people  have also mentioned the CAT can do this, but not sure. Will keep my eye on this and post any updates I have. Maybe we can get this straight. No fun pretending I am riding a Harley///lol (6L redline)

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.

I asked the previous owner if he had similar issues, and if he had a new map to go with the pipe. He said on a different pipe and map that he did, but had the Mistral sorted out. This is the map he said was on the bike: Griso24S-FU2-Mistral-NodBK-5124.2014.10.02.bin, but that’s for a flat tappet bike, yeah?

I purchased a new Beetle map from GRiSO.org, because I want to run with the decibel killer in. This is the map I purchased: Griso24S-FU2-R-Mistral-dBk-4E1.2015.12.29.bin, which I believe to be correct?

The map uploaded properly using IAW Writer.

Some things I’ve checked:
- Right side spark plug was carboned up badly, so I just went ahead and replaced spark plugs.
- Checked all electrical connections to make sure they are connected/tight.
- Pulled gas tank and checked all vacuum lines and fuel lines.
- Checked airbox. Cleaner is good, and box is clean.
- NGK plug wire caps
- TPS reset

For tuning everything checks out:
- .1 and .15 on valve clearances.
- Brand new spark plugs
- Check TB balance with my fancy CarbMate TS-111. They are in balance at 4,000 rpm.
- Bike was recently tuned, so I didn’t expect anything out of whack. But it was good to check.

I've read though this and the other popular Guzzi forums. At this point I don’t know what to do. I’m chalking it up to user error and I can’t see something right in front of me. It does the same thing with different maps, although taking the db killer out makes it run slightly better. An ideas? Injectors bad maybe? (please say no, lol)

Also related: I was hoping to go back to stock since I fear the Mistral will be too loud on longer rides. Problem is I have no way of doing that currently, is that right? Is there a way for me to get a factory stock map?

I have the stock can but no stock map.

I can flick you the stock map if you wish.


.

Heck yeah, man! That would be great. PM on its way

1 doubt that reverting to the stock map will cure it. The Mistral Hi-Pipe maps are Mark's most developed work, lots of us are running them with no issues but it's worth a go.

With the gaskets are you sure they aren't there? Was it making a sort of 'Frappa-Frappa' noise when you goosed the throttle? The gaskets squash down to virtual invisibility in service.

Your suggestion that it feels like it might be going on to one cylinder is intriguing as this would have this effect. Check plugs, leads and caps again.

Pete

Well damn it! Just checked gaskets again. They indeed do squash down to nothing : /

Gouged one pretty badly when poking around with a screwdriver when checking, so still gonna need a new one.

It never did make a noticeable "frappa-frappa" noise. The inside nut on the left side was finger loose when I removed headers. Not sure that matters at this point.

Crap, wanted it to be something easy. sigh

I'm not worried about maps so much, since it's a consistent problem over the two maps I have. Dbk or no dbk, as well.

Really just want the stock map so I have the option of going bone stock. Also, maybe starting from stock will help me wrap my head around this ... I dunno.

I'll check plugs, leads, and caps thoroughly when I get back on Sunday.

Thanks for the suggestions so far. Much appreciated...

When you had the headers off did you have a look up the back of them? One oddity we had was on Mark III's bike in that it had one Japanese market header! These have a secondary catalyser pack inserted into the back end of the header! I managed to get him a warranty replacement but it was very strange! The cat looks like a honeycomb and it will have a serious effect on gas flow, especially if it has been fed raw fuel at any point due to misfiring or the like.

This behaviour, and that of Bulldog9's Norge really sound like some sort of physical blockage to me. Obviously I can't be sure from an ocean away but I'd be seriously checking all the pipes including the headers, pretzel and can for obstruction. In Bulldog's case I'm thinking the cat box may be compromised.

Pete

Just an update. Maybe some more tips or ideas? In the meantime, I'm gonna go pout.    

I looked at all the exhaust pipes, blew compressed air through as well. All seems in proper order. No visible obstructions (or Japanese spec headers).
Swapped out the Mistral for the stock can. Exact same behavior. The map doesn’t matter, either. It does the same thing on 3 different ones.
Unless both cans have a blockage, stranger things have happened, it doesn’t seem to be the pipes or cans.

Bulldog9 explained it best: It’s almost like a switch (at around 5500 rpm for me). I can sort of “blast” through it by twisting the throttle to full stop, but that gets hairy doing that -- it’ll still sputter and buck.

No signs of arcing. Plugs, wires, and caps seem in good order. I replaced all of them just in case though. So I have brand new plugs, wires, and caps and nothing changed.
That’s about as far as I’ll go in blindly throwing parts at it : /

I’m no mechanic, but don’t mind getting dirty and exploring new things. So if there’s any more advice, I am all ears.
The bike only has 3900 miles on it, so I may be under factory warranty still?

Not sure what to do at this point. Nearest Moto Guzzi dealer is in Seattle, nearly 600 miles away. There’s a decent independent shop here and he says he has some experience with Guzzis. They tore into a Stelvio recently he said, so maybe I’ll give them a shot if I get desperate enough.

I’d rather fix it myself, but if it’s getting into electrical gremlin territory then I’m not sure I can tackle that… ugh.

I'm at an impasse until I take the bike for the new Fuel pump/level sender unit. The guys at MI think the fuel supply may be the problem, but untill they rule that out they havent looked much farther. Will be interesting to see what they find.

I guess I could pull off the crossover/compensator and look, but that looks like quite the problem. I'm considering just ordering the crossover/cat eliminator pipe, found 3 sources, Guzzitech, MG Cycle and AF1.  Anyone have any input on the best pipe?  I was thinking of doing this anyway, so may order it while I am waiting for my appt.

This does have me baffled.

MotoMT wrote:

Just an update. Maybe some more tips or ideas? In the meantime, I'm gonna go pout.    

I looked at all the exhaust pipes, blew compressed air through as well. All seems in proper order. No visible obstructions (or Japanese spec headers).
Swapped out the Mistral for the stock can. Exact same behavior. The map doesn’t matter, either. It does the same thing on 3 different ones.
Unless both cans have a blockage, stranger things have happened, it doesn’t seem to be the pipes or cans.

Bulldog9 explained it best: It’s almost like a switch (at around 5500 rpm for me). I can sort of “blast” through it by twisting the throttle to full stop, but that gets hairy doing that -- it’ll still sputter and buck.

No signs of arcing. Plugs, wires, and caps seem in good order. I replaced all of them just in case though. So I have brand new plugs, wires, and caps and nothing changed.
That’s about as far as I’ll go in blindly throwing parts at it : /

I’m no mechanic, but don’t mind getting dirty and exploring new things. So if there’s any more advice, I am all ears.
The bike only has 3900 miles on it, so I may be under factory warranty still?

Not sure what to do at this point. Nearest Moto Guzzi dealer is in Seattle, nearly 600 miles away. There’s a decent independent shop here and he says he has some experience with Guzzis. They tore into a Stelvio recently he said, so maybe I’ll give them a shot if I get desperate enough.

I’d rather fix it myself, but if it’s getting into electrical gremlin territory then I’m not sure I can tackle that… ugh.

Or a TPS problem. If they can plug PADS in they can do a logging run and save the live data for review. If you can 'Blast through it' and it's fine at the top it may be a dirty spot on the TPS rheostat coil.

Pete

So related to TPS: When connected to GuzziDiag, is the TPS value supposed to fluctuate while the bike is running at idle? I just noticed this last night. It was going down to 4.2, 4.1 then back to 4.6, 4.7, 4.8.

Also, a bit more info after replacing the exhaust gasket that I gouged up: 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. This is with the stock map and can. With the Mistral and respective map it was noticeably better, but still not very rideable. At least it didn't feel dangerous. Not sure if that's any more help, but figured it's worth mentioning.

I found a thread from the previous owner, but forgot to bookmark it. I'll dig it up and post a link. He exhibited similar behavior, but at a higher RPM than what I'm experiencing. Maybe it was the start of something that has gotten progressively worse ...

Thanks for the continued help and responses

Oh and Bulldog9, definitely keep us updated on your progress. I'm curious if we have the same issue.

MotoMT wrote:

So related to TPS: When connected to GuzziDiag, is the TPS value supposed to fluctuate while the bike is running at idle? I just noticed this last night. It was going down to 4.2, 4.1 then back to 4.6, 4.7, 4.8.

Fluctuations at idle are normal. Typically, it will go to a higher value, say 5.1. However. I've not seen one go low, but that doesn't mean anything.

Are you sure the plug caps are good?

Pete

Well I'm not sure of anything anymore, lol. Any tips on how to thoroughly check them? I see or hear no visible arcing. They are securely fastened.

Turned out lights and see no arcing. Grounded a screw driver shaft and ran along lead, no spark jumped to blade.

I have some ends and 7mm wire, but no extra caps. Just to check, and be thorough, could I crimp up some straight leads without a resistor cap? Our plugs are resistor plugs, so is the cap needed? Don't want to break anything, so won't try until somebody smarter weighs in ; )

NGK SBO5E caps. Try. They do fit.

Those are the caps I have currently. Sorry, forgot to mention that.

On my 8V motor, the problem was unchanged from stock plug caps to the new NGK. In fact, I have a miss now on CYL 2 after the cap change, but that is neither here nor there. I'm not happy with the current setup of cut stock wires and screw on caps. Am going to look into some changes this winter.

The drop off issue is pretty consistent, bogs down and doesn't recover, and is definitely not TPS related, it is RPM and LOAD related. Full WOT or part throttle it pulls till 6000 RPM and then almost like a switch goes flat. OCCASIONALLY will break through, surge and then sputter again, but rarely. Mostly it sits at 6500 and loses all power. If I back off the throttle to a low load, it will rev to redline, but any load causes it to fall flat.  

It also feels 'clogged' on normal running and doesn't rev freely or eagerly like my GRiSO. So...... with the idea of a possible clogged cat and increased back pressure causing the issue, for kicks, I took off the stock can and rode today. Idle seems stronger, motor revs freer, but still bogs and falls off at 6K, and little change with the power fall off. If anything, it was a bit smoother in the drop off and was able to climb and pull a little better. With the can on the motor mostly just hovers at 6500 and goes blaaaaat and taking 30 seconds to climb closer to the 7500 rev warning.   The bike has YET to hit the rev limiter.

With the can off, it takes maybe 10 seconds to climb to the warning light, but doesn't hit rev limiter.

It really really acts like a governor.

MI will check the CAT when I bring it in.

Bulldog9, that is a great explanation. Couldn't have said it better, and exactly what I'm experiencing. Thanks for the update. I'm eager to hear what Moto International techs have to say.