Strange Fueling Issues GRiSO 1100 07

I had some issues while riding home on my fly and ride.
The bike ran flawlessly for the first two days other than some popping on decel which was not too bothersome.
No missing no hesitation, and good power delivery from all RPMs. I took it up close to redline a couple of times and it pulled strong and smooth.
The problems started after it was left out in the rain for a couple of days.
When I filled up with gas a bunch of water went into the tank as I opened the gas cap. The drain hole was clogged and I was unaware of it.
I removed the injectors and used Guzzi diag to pulse the injectors many many times into a container until it seemed it was just gas that was being expelled.
This took an hour or two as it was a slow process. A lot of water came out, about 3 times as much on the left as the right side. I added a half bottle of Heat, which is a moisture remover to the full tank of gas.
I buttoned it all back up and was able to get it started. It coughed and spit quite a bit as there was still some water left, but after 5 minutes or so it smoothed out and idled and ran smooth while riding.
I took off the next morning and the bike ran perfect again for over 350 miles.
The last 50 miles it started cutting out like I had quickly closed the throttle and then would catch again a few seconds later. This got more frequent the farther I went.
The last few miles to my friends house it was almost unrideable.
After resting for an hour and unloading the bike, I went to investigate.
I opened the gas cap and heard a whoosh from what appeared to be a vacuum in the tank. I was almost on reserve, so it had been about 150 miles since I had last filled up.
I also then blew out the drain line with compressed air and heard what sounded like a spit ball being expelled from a hose near the rear tire. I sprayed some wd40 down the hole and with a little air it sprayed on the rear tire.
I then took the bike out for a 1/2 mile or so and the cutting out had stopped.
I did a 20 mile ride the next day and filled up with gas again and the bike was running great.
I then left for my 550 mile ride home on the interstate the next morning.  
The bike started out running great, but as the gas got lower I experienced the cutting out and also sometimes if I would roll on the throttle it would not accelerate just like it was not getting any more fuel. This is the most common symptom now.
I think it was usually fine if I had a full tank, but this problem seems to be getting worse.
I have not pulled it apart since I got home yet, but I will next weekend.
The tank will be off and completely drained.
I have a new fuel filter and I am ordering some SAE 30R10 submersible hose to do the inside filter and pump fix.
I will also be cutting off the molded plastic hose that goes to the Y and then the injectors and replacing it with regular high pressure fuel line with the proper hose clamps.
At this point I will inspect everything and hopefully see what the issue is.

I was wondering if any of you have experienced similar issues and what you did to remedy it.

Does it still have the charcoal canister fitted? It sounds to me like the vent system is blocked so air can't get in to replace the fuel as it is used.

Yes it still has the charcoal canister. I am going to pull that off. Is it recommended to do that?

I never had a problem with the syste on any of my bikes in the US and we don't have it here but I'm given to understand that it can cause a few issues, mainly with starting in hot weather. If though the tank cant 'Breathe' through the system then the tank will depressurise to the point where the pump can't overcome the 'Vacuum' in the tank. The lower the fuel level, the greater the issue.

I was assuming that the vacuum in the tank was a highly probable cause. I am not familiar with the GRiSO and I am planning on thoroughly inspecting and tracing all the hoses when the tank comes off to understand how it is plumbed and works.
I generally like to remove stuff to simplify if it does not impact the running of the bike.
There was a couple of clear plastic hoses that hung below and fell off the bike on the trip. They were brittle, and I am not sure where they went to. I imagine I will find out while the tank is off too.

Is the GRiSO tank like the 750 Breva tank, in that the latter has 2 drains moulded in the wall, one for excess fuel, and the other for liquids in the tank cap surround? Those plastic tubes sound like aftermarket drains - originally rubber, but they get hard, brittle & break with age. On the Breva there are aluminium nozzles set into the bottoms of the drains to which the tubes attach. On a mate's Breva the one to drain the water from the tank cap was corroded & blocked, so water ended up in the tank and rusted parts of the fuel pump, enough rust to stop the pump working. We drilled out the nozzle & replaced the fuel pump to fix the problem.

I imagine it is similar to the Breva 750. I also have a Breva and have had the tank off a couple of times.
Next weekend I will pull the tank and find out what goes where and test for blockages.
I hope I don't have to replace the pump. I don't think the bike has ever seen rain until I took it out in it.
It was a garage queen (maybe princess) with just 3K miles. I also think the tank has never been off before. She is almost a virgin if that even is a thing?

As the charcoal canister is still there, I'd suggest that after 12 years it is likely 'not at its best'.
Performing a canisterectomy is recommended. All it does is save the planet from rogue gas fumes...

Mine was two weeks old when it came off.

bahamazoo wrote:

Mine was two weeks old when it came off.

What took you so long Son!

something called warranty.... which was in play due to a faulty lefthand switch block... then, as was shipping her out of the US back to Oz.... nah, void away!!

I know what you mean as far as warranty but I do not trust any dealer in my area to mess with my bikes.
It's that bad.

haha, I was living just down the road in Fort Ladedah at the time.... local dealer -I think it was Atlantic in Pompano.... had Trumps and Ducks as his main stream, but also carried Gootsies.
All they did was swap out the switch block under warranty.
They were handy for the first service, and then when I shipped the bike out, they collected it for me, washed and crated her up - on a steel Trumpy pallet, and a Duck cardboard box over the top , and loaded her up on the truck for me. All for the price of a (unneeded) service and a six pack

bahamazoo wrote:

They were handy for the first service, and then when I shipped the bike out, they collected it for me, washed and crated her up - on a steel Trumpy pallet, and a Duck cardboard box over the top , and loaded her up on the truck for me. All for the price of a (unneeded) service and a six pack

You got a good deal. Wouldn't be great if all dealers were like this?