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Audace stumbles on WOT

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toomanybikes:
I've recently experienced some strange and intermittent fueling behavior.

When the tank is relatively low, like three bars or less, the engine will momentarily bog down under sudden heavy throttle, almost like it was running out of gas, but the tank was not empty.  Gradually rolling on the throttle is fine. Filling the tank resolves the problem, but it's not yet clear if it's a fuel level thing or just relieving built up pressure due to clogged vents. The vent tubes all seem to be in place, but I have not yet removed the tank to see what lies beneath.

The bike was a rescue after sitting for unknown years. The tank does not have any sludge in it, but the filter and pump are probably the original.
I'll plan to empty the tank and replace the filter, but should I look for anything else? The pump seems to work fine, except the weird fueling at low levels.

The bike has the stock airbox. I replaced an airbox hackjob by some previous owner. there are no indications of flashes or mods.

It *probably* still has the fuel vapor recovery system in place since I can see the pressure valve attached to the vent tube coming from the fuel opening. It's possible someone messed with that system, given other mods that were done and indications that someone took the tank off previously.

The fuel cap flange spacer is in place with a tiny opening near the vent barb. See pic.

Any suggestions beyond "open the cap perdiocially"? That's one likely easy fix, but I'd rather understand and fix the underlying issue.

Moparnut72:
Having owned an Audace I would check the filter first thing. The evaporative system is pretty benign so I doubt any mod to it will help one way or another. I did mine as recommended by a well known shop owner. It didn't make the slightest improvement in the low gear low rpm surging. During the time I had the bike Beetle wasn't releasing his map for it due to an issue. He has one now.
kk

toomanybikes:

--- Quote from: Moparnut72 on November 25, 2025, 08:41:58 AM ---Having owned an Audace I would check the filter first thing. The evaporative system is pretty benign so I doubt any mod to it will help one way or another. I did mine as recommended by a well known shop owner. It didn't make the slightest improvement in the low gear low rpm surging. During the time I had the bike Beetle wasn't releasing his map for it due to an issue. He has one now.
kk

--- End quote ---

Thanks. Here's a pic of the pump/filter assembly. Any input on if the hoses can be re-used? I know the oetiker clamps are one and done.

The evap system seems to be in place, tucked in behind the starter motor, with at least the primary hose still connected. A few of the other lines were left unattached, although one is probably for the fuel tank vent line not the evap system.

Moparnut72:
I bought mine kind of used, 500 miles, from a dealer repo'd due to a fraudulent credit ap.  It had originally spent 3 years on the dealer's floor. When it was being checked for me it dropped a valve at least that is what I guess from what I was told happened on a test ride. I had the tank off for another mod and found that the tank vent hose wasn't connected to anything. I think the mechanic who replaced the engine left it this way. I really liked mine but selling it was the start of my downsizing due to age, it was a handful to ride at walking speeds. It was a major mile muncher.
kk

TN Mark:
Does your tank make the moaning whale sound? If so, you likely found part of your issue. Also, on the riders right hand side of the intake plenum is a vent that goes from the charcoal canister to the intake. That connection can sometimes be less than hand tight. It’s best to remove that and put a bolt in the plenum instead.

If you do an internet search on moaning whale Moto Guzzi 1400 and tip over valve remedy, you will very likely find the solutions to your issues. The Tip Over valve is often a particular source of frustration on the 1400s. I gutted mine recently following the instructions to the T.

Also, if you have the 2016 and earlier firmware in the ECU, that was also quite poor. If going to a dealer is an option to get the latest 2017 firmware downloaded into the ECU that may also work. The ECU on the 1400’s was specifically designed not to receive aftermarket downloads. The last thing you’d want is to brick the ECU.

Also, your fuel filter is the good type. Some of the earlier ones were half metal and half plastic that was sure to deform. If you haven’t yet, pouring a can of Seafoam in the tank and running it through is also a very good idea.

But confirming the mechanical issues are solid is your first coarse of action.

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