bogging/sputtering off idle

[spyd3rm4n]

I recently picked up a 04 FZ1 that's been sitting a long time. Previous owner started to fix it by installing new spark plugs and a new generic amazon/ebay fuel pump, but abandoned the project when he realized the carbs needed to be pulled.

Carbs were clogged (pilot jets blocked completely!) so I removed them and got the bike running. It starts and idles perfectly, and I can rev it out just fine in neutral. I went to take it for a ride today and it was fine, but after a few minutes it started bogging badly whenever I gave it throttle. It's sputtering and struggling to accelerate, then eventually the RPMs climb and it revs out just fine. Then it ran fine for a while, then the problem came back off and on.

I disconnected the fuel hose inlet at the carbs and when I turn the ignition on, the fuel pump easily runs and pumps fuel so I don't think that's the problem, but I guess it could be possible. The lines aren't kinked either. The airbox looked fine though I still need to check for any obstructions between the filter and carb inlets.

I didn't adjust the TPS but went through the diagnostic steps and when I reconnect the TPS connector with the ignition on the tach needle is bouncing erratically from 5000-6000 rpms. Could this be causing the issue? What else should I be looking at? I still want to remove all the spark plugs to confirm their condition and check the coil connections.

 

[Isleoman]

Could it be one of the other jets or something else in the carbs?

There's a breather in the fuel cap that prevents vapor lock. Easy enough to clean and rule out. The fact it's pumping with line removed says that's likely not the issue.

I've learned from experiment that you can loosen the TPS and drive around adjusting it from one side to the other and it makes little noticeable difference, so I don't think that's it.

Agree on the plugs check to make sure they are all firing. If it runs fine now in neutral , and all pipes are hot that kinda says they are firing. Look around the the leads and contacts for the two coils to make sure they aren't arcing to the frame.

Does airbox looking fine mean you've taken the filter completely out for inspection? Dirty air filter and clogged carbs are associated with hesitation.

 

[spyd3rm4n]

Could it be one of the other jets or something else in the carbs?

I had the carbs off the bike twice last week, cleaned all the jets and passages as best as I could. I guess it's possible one of the bypass holes under the butterflies is clogged. But this behavior has me thinking maybe a needle holder popped out of the slide?

When I had a clogged pilot jet on my silver 2002 it sputtered when I revved it, but had a cold header and lumpy idle along with it. This one's idling fine, and even revving in neutral it's smooth (after it's warmed up of course!)

There's a breather in the fuel cap that prevents vapor lock. Easy enough to clean and rule out. The fact it's pumping with line removed says that's likely not the issue.

I've learned from experiment that you can loosen the TPS and drive around adjusting it from one side to the other and it makes little noticeable difference, so I don't think that's it.

Agree on the plugs check to make sure they are all firing. If it runs fine now in neutral , and all pipes are hot that kinda says they are firing. Look around the the leads and contacts for the two coils to make sure they aren't arcing to the frame.

Yeah, all pipes are hot and firing at idle. I need to inspect the coils and plug wires. It looks like the previous owner replaced all the plugs as they appear to be brand new, maybe one wire isn't seated all the way? Plugs/coils and wires are next on my list to inspect. I'm leaning toward an ignition issue since it's happening under load.

Does airbox looking fine mean you've taken the filter completely out for inspection? Dirty air filter and clogged carbs are associated with hesitation.

I had the air filter out for inspection and there was some debris inside it but not too bad, I tapped out what I could. I didn't inspect the inlets to the carbs but I will certainly check those, however once the bike eventually revs out after the hesitation it seems to run fine... making me think maybe a loose needle?

The fuel in the tank was a mess when I got the bike. I did drain each of the float bowls into a clear container and a little brown water came out, sinking to the bottom of the container. This was after I had the carbs out for cleaning and let the pump run about a quart of fuel from the tank to the outlet, I thought this was enough to flush the system but I guess not. While draining each float bowl individually I left the drain open and turned the ignition on to let the fuel pump run more fresh fuel into each carb, but it's still bogging.


https://imgbb.com/

 

[spyd3rm4n]

I started some diagnostics, also tackling a coolant change and AIS removal while the radiator is drained, making easier access for the spark plug change. The 20 year old coolant is disgusting.


picture uploader

The air box is clean, no obstructions between the filter and the carb inlets. I do need a new filter as the foam on the bottom and top is very sticky.

I only took the #1 spark plug out so far and learned it was fairly wet after the bike had been running. The plug wire wasn't twisted into the boot all the way, I was able to get over two full turns to snug in in there. Prior to the plug removal all four headers were still hot at idle, sprayed water on them and it sizzles and immediately evaporates. Bike idles and revs perfectly ine on the center stand, though there is some condensation coming out the tail pipe. I can still see a small amount of water in the tank settling in some of the low spots, maybe an ounce total. Need to get a small hose and vacuum pump in there to get all that out.

This got me thinking there's still some residual water in the fuel system despite draining the float bowls and letting the pump flush some fresh fuel into a bottle. I removed the fuel filter and discovered a lot of junk that came out of the inlet. (disregard the orientation of the filter in this photo, all that junk came out of the fuel filter inlet)



Could a partially blocked fuel filter and some water in the system be causing this bogging ??? Pump appears to move a decent volume of fuel despite all that junk so I'm thinking it still might be the water in the system.

As I said earlier if none of this solves the problem, I'll remove the carbs again. Still could be a needle holder that popped loose.

 

[bunk]

DANG!

 

[Isleoman]

That's some serious crap in that filter. I'd buy a pack of them and keep changing them till it runs clear. I can see how that would gum up the carbs quickly.

 

[spyd3rm4n]

That's some serious crap in that filter. I'd buy a pack of them and keep changing them till it runs clear. I can see how that would gum up the carbs quickly.

Luckily the filter stopped most of that - bits of the petcock screen that disintegrated along with tank rust. I didn't see anything downstream, I cut the filter apart and the paper element stops nearly everything. There are also screens on the carb inlets. Even when I had the carbs out, after the previous owner tried running the bike on that nasty stuff, there was no grit in them just stale old fuel and varnish.

I am more concerned with the water I drained from the float bowls. Need to get all of that out of the tank as there's still some left.