T500J idling too fast

[garncarz]

I'd like to ask for some advice on an issue with my recently acquired T500.

Here is the background: I acquired it about a month ago. Looks pretty much 100% OG. The previous owner said it started idling fast recently (about 2200 RPM's). Can’t get the idle any lower.

I have so far:
• Cleaned both carburetors 2x (carb cleaner, ultrasonic bath, blow passages out with compressed air).
• Built an air leak test rig, attached to the manifold side of the cylinder and plugged the exhaust port. Both cylinders hold 6 PSI for an hour.
• All carburetor brass is OEM mikuni and original T500 stack.
• Replaced the rubber intake tubes.
• The air fuel mixture screw is set 1¼ turns out.
• Idle speed screws are set so slides are up 1mm from closed.
• Both carbs synchronized.
• Compression is 145 left/148 right
• Cleaned baffles.
• Set the points and timing, new B7HS plugs gapped at 0.6mm
• Cleaned petcock (good fuel flow)
• New coils, HT leads and right condenser.

Spark plug rings are black and wet but the electrode and insulator are brown after a 20 mile ride. Not sure where to go from here, any advice would be greatly appreciated. TIA.

[karl pa]

While in the carbs did you check choke plungers? Plugs wet and black sounds rich mixture, if choke plungers hard and leaking could cause excess fuel through.

[karl pa]

Also, do you have the early carbs or later carbs? are they vented to atmosphere or sealed? Early and later carbs use totally different jetting.

[garncarz]

I didn't spend much time on inspecting the starter plunger, I'll have a look today. Also, I have the VM32's (later?). Vented to atmosphere? 'Splain?

Also, I misspoke about the plugs. The rings are black and wet but the electrode and insulator are brown.

Jetting:
Jet needle - 5FB8
Clip - 3
Needle Jet - P4
Main - 150
Pilot - 30
Valve seat - 2.5 (polished)

Float height - 27mm

T500 plugs.jpg

[karl pa]

I think the 72 and earlier came with the hemispheric pressure carbs, they are not vented to outside pressures, they used the 150 main jet, the later carbs that are vented use 97.5 main jet. I am not familiar with the early carbs.
You can research oldjapanesebikes.com, Ian has section on field guide to T500/GT500

[garncarz]

Figured it out! Throttle cable was routed wrong and was binding. Wouldn't let the slides all the way down. Cleaned, lubed and rerouted....nice 1300 RPM idle. Thanks for everyone's help.