Idle fading away......

Okay guys this is really weired and I sent pm's to BigFitz and Rick-O-Matic.
Checked everything they suggested but something still isn't right. Mind you I had this bike running perfect for 2 years then all of a sudden......
Still starts easy, choke works great, color tuned, sync'd perfect, floats double checked and they are perfect, no fuel leaking out anywhere, no cracks in any lines, air filter is clean and I had my son do another cleaning on them even though they were just cleaned by Rick 2 years ago. What is happening is it doesn't want to stay at idle. It will idle for a short time then it just starts getting slower and slower until it dies. I know it is actually suppose to idle I think around 1100 but I have to set it up to about 1300 to get it to idle for at least a little while. This one has me baffled.
Anyone else have this problem and if so what was the solution?
Iwanted to add that the idle was fine when we first put the carbs back in.... I let it warm up then we checked the color tune and the sync. It wasn't until I took it for a ride that the idle started doing this again. I got about 2 miles out and I noticed at a stop sign that it wasn't wanting to idle right so I went back and when I got back this is when it didn't want to keep running at idle.

 

Gas cap vent? Take the gas cap apart and have a look. See if it will idle with the gas cap open.

It sure seems like a fuel supply issue of some sort. Inline fuel filter need replacing?

Petcock OK? Will it stay idling on "PRI?"

The 550 is supposed to idle at 1200.

The only other thing I could think of would be the battery, but you said it starts right up.

 

New fuel filter, petcock is new, runs on PRI but does the same thing by not wanting to idle, battery is top of the line and it is good. The only thing I haven't done is try to see if it idles okay when the cap is open but it has been rebuilt also.
Will try it though.

 

Just tried running with the cap open and after about 7 minutes it started doing the same thing.
Got idle set at 1200 but it seems to act up once it gets hot.
What would cause this?

 

Water in the gas tank could cause those symptoms too, just thought of that. Or bad gas?

 

Nope, I pay $4.59 a gallon for the best gas I can get. It is non ethenol premium. What else could be going one? This is what I mean..... I just don't get it......
I just put some sea foam into the tank and I thought I would drive it for a week to see if it clears something out. I don't know what else to do.

 

How much you pay, and where you get it, doesn't preclude getting contaminated fuel. Drain the float bowls and have a look at what comes out.

 

k-moe, way ahead of you. Did that a long time ago. Please read all that I have done already. I do know kind of what I am doing. I have had this whole bike apart. The gas is fine. I was just saying that it is the best I can buy in this area. Been using the same gas from the same place for over 2 years. This one just has me really thinking.

 

OK....... If fuel delivery isn't an issue then it might be time to move on to the WAG portion of fault diagnosis.

The only other thing that I can think of that would match the symptoms you describe is a soft-seize due to overheating, or inadequate oiling (remember, this is a WAG).


One last thought...do you have an inline fuel filter installed? Does it have a paper element?

 

Here's another WAG; how many miles have you put on it in those two years? Do we have a tight valve here?

Although I have to agree about the source of the gas being no guarantee you didn't pick up some water.

Due to the shape of the fuel tank, you wouldn't be able to see a "blob" of water sliding about on the bottom.

Just based on the circumstantial evidence of the sudden onset and the fact that everything mechanically should be fine, I'd DRAIN THE TANK completely to be sure.

I'd consider it more likely that you've got some water in the tank than I would a new and dire mechanical condition.

 

Have you checked compression recently? How does your oil look? If it isn't a gas flow/H2O problem I would suspect it's getting too hot, maybe an oil flow problem since it crops up after 7 minutes. That is enough time for it to start to get really hot if oil isn't moving properly. Are you sure it's not too lean a mix? Once it reaches that 'un-happy' temp it will idle downward until stall.

 

i have been dealing with the same issue as the OP, but i also havent done the things he has to diagnose it but i have been running, im pretty sure anyways, lean for awhile now. you suggest that could have something to do with it? i just thought i needed to reclean the carbs, but after reading this thread im not sure that is the problem necessarily. it is super annoying to always have to finesse the choke at stoplights to idle.

 

Although our XJ's are really quite straightforward engines without 1/4 the BS modern engines are saddled with, there is almost always more than 1 thing that can create symptoms.

That being said, an idle that changes as you ride and as the engine warms up is usually one of two problems. 1-tight valve(s), 2-getting too hot. The valve is a simple cause and effect and easily remedied. Getting too hot can be multiple things but is most often either a lack of oil flowing (in airheads), or a lean mix. reduced oil = reduced cooling and increased friction, and lean mix = no added cooling from excess fuel mix evaporation. If the whole mix gets burnt because it's lean, then the head and valves will progressively get hotter because they rely on a little extra bit of fuel/air mix to help dissipate excess heat. Once the engine begins to get too hot the tolerances start to break down and compression will drop, power will drop, idle follows, and eventually oil is seeping past the rings fouling the mix and the engine will stall-if you are lucky it will happen before you melt your motor!!

So yes, one very important sign of a HEALTHY, happy motor is a steady idle.

 

very well stated, can def appreciate that info. thanks!