float height pic no .2

picture of level of float height after riding for 5 mins

 

If the level is fine before the ride as you've checked.
After riding the level drops as shown in above picture.

Suggests to me you have a fuel supply problem.
If it's only in the one carb I would pull the float bowl, remove the float, and remove the needle & seat. Check the back side of the seat, usually there's a fine screen attached and it may be plugged. You may want to check all of the carbs screens just in case. Run some fuel or blow air thru while you have them apart to flush what ever may be lurking in the lines.

 

Good call, Nick. Also, the passage that runs between the carbs may have something blocking it too. More than likely, some particulate broke off from the failing petcock seal and is blocking the needle valve. Double check your fuel line while you're in there to be sure that it hasn't broken down on the inside, introducing crud into the carbs.

The CORRECT way to measure float height is with the tang on the float GENTLY resting on, but NOT collapsing the needle. If the needle has a very small "plunger" that is under the float tang you want to be sure NOT to collapse this when measuring float height. Normally, float height is never measured with the carb upside down, but held a a bit of an angle to get the float - needle relationship just right.

However, each carb can be a bit different, consult the book.

With the float in the correct position, measure from the highest part of the float down to the MATING SURFACE of the carb body. that is your float height.

Decreasing the float height INCREASES the fuel level...
Increasing the float height DECREASES the fuel level...

And a small adjustment (.5-1.0 mm to the float height) can cause a big difference in the fuel level, which in turn can make a huge difference in the way the bike runs...

This is probably way more information than you need to know to fix your problem, but is good to know nonetheless...

good luck!

-Matt
83 xj9

 

You might also want to try pulling the tank and getting the fuel below the petcock so you can check the petcock fuel supply outlet for some obstruction.

Remove the Cross-Head screw below the Petcock select knob. Don't let the small nylon washer get away on you.

Shine your penlight in there and look for any foreign matter that would cause blockage. Probe in there to see if there's anything blocking. Q-Tip it with carb cleaner from both openings.

This is just another base to cover.

 

i put a brand new petcock on there and fuel line from the petcock to carbs and in-line fuel filter also brand new and i checked the fuel pipe that connects all carbs and it was free and clear, also small screen on the seats and they look o.k to me so am thinking that it is either the needle or it is not seating properly, the needle doesnt appear to look damaged, it doesnt look any diferent than the others. i am going to go back over everything to double check, thanks for the suggestions everyone.