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Old 08-15-2017, 08:22 PM
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TopCatGr58 TopCatGr58 is offline
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Join Date: Jul 2002
Location: Portsmouth, Va.
Posts: 12,619
Hey again,

Okay, just as another member with leaky carbs found out, the later model carbs not only have rubber/viton tipped float needle valves that can compress/get grooved and even breakdown, but the seats also use a Viton O-ring to seal it, and it also can breakdown and shrink, and then it will allow it to leak as well. SO...you WILL have to take the carbs off to clean and replace these parts.

Now, with them leaking, they could be flooding a bit and that can cause problems with throttle response and such. Now the XJ has the centrifugal advance curve programmed into the TCI. The Vacuum adv. curves are also programmed into the TCI but are triggered by the vacuum sensor box. But the vac. adv. portion of the timing curves are more for providing fuel economy during cruising mode, and it actually releases/retards excessive amounts of timing advance back to the more power producing point of ~35 degrees BTDC which is controlled mostly by the TCI and just the engine RPM itself, so I don't believe any stuttering in other gears under accel are being caused by the vac. adv. module.

You're right in that there are several different ports in the carbs that provide fuel at different throttle inputs. The Pilot jets and circuit are responsible for the low rpm response up to about 3-4k rpm. That's where the carbs transition into using the MAIN's. They don't clog quite as easily, BUT they and more likely their emulsion tubes(Main Jet NEEDLE) can get gummed up and clogged, and that can also cause poor throttle response. So...again, getting into the carbs to a proper cleaning while repairing the float seat O-rings and float needles looks to be in your future.

You can try to use some SeaFoam or Techroline fuel additive/cleaner in the gastank, about 1/3 of a bottle or so each tank, and run it through to see if it might provide SOME measure of cleaning/clearing the passages and gum/varnish from the carbs/jets/emulsion tubes which might help with the throttle response, but it's a bandaid approach to major surgery!

If tearing into the carbs seems too daunting, I'm sure there are several Xsives in your area that would be willing to lend a hand to HELP you, not necessarily do the job, but assist you in doing it so you can learn and get it done right and relatively cheaply vs. trying to get a dealership/bike shop to do it! Also be sure to get GENUINE MIKUNI parts, we have found aftermarket are inferior, incorrectly sized/metered and just add to the problem!

Your bike has the newer 3 ohms style coils, but both your plug caps and wires can still develop corrosion and cause weak/poor sparks, so taking the caps off/unscrew from the plug wires, inspect central wires, if green with copper corrosion, cut of 1/4" at a time till clean coppper wire, and also clean screw inside cap, and then reinstall. While at it, Ohmeter the caps while off, should only be ~5 kohms, if much higher, then internal resistor and spring/contacts have corroded or gone bad. You can take them apart at the spark plug end with a straight screwdriver, remove parts, clean and retest/ohmeter resistor piece. If still way over 5K, then replace caps. Sometimes engines/carbs have electrical problems!

T.C.
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