my xj700 is only firing on 3 clylinder

i got this 85 xj700 and the rpms wont go above 4500 i cleaned the carb 4 time,and still the same,i check wire all juiced up,new caps new plugs & filter,could my vavle be doing this,

 

Have you tested your ignition coils and wires to make sure you have spark on each plug? Remove all plugs and install one on each wire, lay the plugs on the cylinder head and try to start. Look at each plug to see if there is a blue spark.

 

My buddy battled this problem with his 700. I believe he had to replace some plastic inserts where the plugs fit, they cracked and the spark took the path of least resistance.

 

What Cylinder is missing?
Does it miss all the time?

Does it "Kick-in" when you get-on-it?

Is it the same Cylinder that the Petcock Hose is attached to?

 

Start the bike, let it get good and warm
spray some water on each pipe to see which one isn't firing
Check for spark by grounding a plug on that wire and hitting the starter button
Check your CDI which is under your left side cover for a good connection (it'll be about the size of a piece of bread with a red sticker on it, right behind the silver stainless steel looking thing)
To do the above step get some good electrical cleaner and some dilectric grease to ensure it's a good connection. (I had a bike do something similar and it turned out to be an intermittent spark on the CDI. It was fixed with a pair of zip ties)
Ensure that the idle mixture circuits are clear...that's the little brass screws on the front side of the carbs. I had another bike act like yours, and I got so sick of it, I hit the mixture passage with an air hose and she fired right up (make that two bikes )
I'd go to a bike shop and buy 4 new spark plug caps. They're $5/pc and it's worth it and you will probably see a gain regardless.
Get back to us and let us know what you have done

 

thanks ,i tryed all that stuff,i checked my vavle today and there all almost closed,i can barley get the smallest feeler gage in them,not good going to get new shims,could this be the proublem

 

Yes ! Acompression test would have revealed it.

While your tools are out, check your rear brake \/\/\/

 

I was going through the same thing early last month. Went through all kinds of stuff, pulled the carbs, pulled them again and had another list member check them, too.

Long story short, found the problem three days ago.......loose plugwire cap. I tightened the daylights out of it, and problem solved.

Dave

 

I have found that the Screw-in Plug Cap can be problematic.

The Cap screws into the Plug Wire. The sharp "Self-Tapping" screw cuts the Core Wires and severs them after time.
Yanking on the Plug Caps to change Plugs and do other maintenance exacerbates the situation.

Loose Plug Caps cause Ignition issues. Tightening the Caps over and over chops the core and soon-enough, you loose Spark.

To treat a Chopped-core Spark Plug Wire which cannot be trimmed-back any further:
Take a short length of the solid-copper Ground Wire you can take from a scrap of Household Circuit Wiring.
Cut the end on a angle or sand it to a point then push it up into the end of the Spark Plug Wire as far as it will go.

Clip the Insert off cleanly at the end of the Spark Plug Wire.
Add two layers of Shrink Wrap.

Screw the Plug Cap back on the Wire nice and tight.
You'll be getting all the whack the Coils can jolt-out.