Carburetor very high idle no matter what... Where to begin?

Alright. New to XJ bikes but not new to mechanics. I understand that my issue is probably due to some part of the carb stack being dirty or sticky.

The problem: bike starts fine, idles nice, warms up... As soon as I crack the throttle to rev it up, the idle stays very high. So high to the point where I need to put the choke on half way to ride it and to calm it down...

Questions: if there's a stuck butterfly, why would the bike start up and idle fine prior to a throttle blip? It is my understanding that a stuck butterfly would remain open no matter what therefore causing a high idle no matter what phase the engine is in or the temperature.

If the bowls are too full of fuel and remaining too full would that be a petcock issue rather than a carb issue?

Is there a complete fuel shutoff on this petcock so I can service or does it just go to reserve?

Is there a certain place I should start with the carbs first?

Do I need to just plan on a full clean and rebuild no matter what?

I am not trying to cut corners or make more problems, I am looking to learn as I go and am certainly ignorant when it comes to carburetors as a whole. I am not cocky and I love to learn from feedback, please help me take a direction and explain why this specific issue is happening.

 

Your symptoms are typically caused by a lean condition or being out of sync. Common causes of lean are vacuum leaks or dirty idle passages.

If the bowls are too full it is a float/float valve issue. Petcock is only to switch the fuel supply.

It is an automatic petcock. When it is set to "ON" or "RES" fuel should only flow when there is engine vacuum. The "PRI" setting bypasses the shut off valve so you can pre-fill the bowls if they've been emptied fo some reason.

If the motorcycle has been neglected you are likely going to need to go through the carbs.

There is a complete carburetor tutorial in the XJ FAQ board.

 

Archifx,

Take a look at your first thread, your questions have been answered on the first thread.

You should not be running the bike if you have contaminated oil and you should be taking the carbs apart and clean them. A link to the church of clean is on your other thread.

There is not point on going any further until you do that since to many variables are going to change.

Cheers.

 

Gas in the oil is a carb problem, pure and simple.

Plan on a full "field strip and service" at the very least; possibly a full rebuild.

Then you will need to adjust the valve clearances so you can properly adjust the carbs; and fully rebuild the brakes.

I strongly recommend a service manual; you're going to need it.

I also believe you've been given these same answers in your previous thread.

Simply asking the same questions all over again because you didn't like the answers you got the first time is known as "fishing for answers." As the Dragon Warrior so succinctly pointed out, this same question has already been answered in your first thread. And go figure, you're getting the same set of answers in this one. The only problem is making us do all this double typing.

 

Thanks guys. Not looking for a different set of answers... I did not have any gas in the oil. Let me make that clear. How do I know? I literally tasted it pouring from the box then did a compare and contrast with new oil.... No gas what so ever. Once the excess 2+ quarts was drained from the system, all is well with that issue.

The oil coming from the airbox on previous thread was new oil from recent purchase by previous owner. I know the carbs are bad from previous thread...

That being said, I was looking for a place to start and trying to critically think the cause and effect of such symptoms. The answers are broad... Fully rebuild carbs then problem solved, etc.

I'm just looking for cause and effect scenario so I can fully understand the anatomy of the issue. MiCarl helped me. Thank you.

Sheesh.... You guys are a tough crowd. Love the "tough love" not looking for trouble, just help and some kind suggestions. I run 302budgetbuild and mach1restoration dot com and love to help others with my websites and builds, since this is a new endeavor, I want to learn as much as possible when I encounter such problems.

Obviously, I'll be attending the church of clean.

 

I can tell you that the carbs on these bikes, as Fitz puts it, "reward the owner with precision." I have rebuilt two different sets of carbs and it really isn't that difficult. The final tuning of the bike isn't tough either as long as you were super disciplined during the cleaning and rebuild of the carbs. Double check everything, take no short cuts, make sure the valve clearances are in spec, Turn your idle knob in half way then to a bench sync of the carbs. Make sure you seat the butterflies really well as there is some adjustment with them, Use real silicone grease on the shaft seals...don't be a miser with it either. Set your a/f pilot screws out 2 3/4 turns from "soft" bottom. Wet set the floats while level on a bench from left to right and forward to back to spec. Make sure the o-rings are seated correctly on the pilot screws ( I like to insert the screw. assembled with the spring, washer and o-ring with the carbs upside down in one hand to insure the o-ring does not come off the pilot screw.)
Any and all of these things will make you crazy if they are not 100% correct.
There are no short cuts, magic liquid, witch chant that works..do it right and complete the first time and be done with it.....and then enjoy riding a real fun bike!!

Hope this helps