I recently rebuilt my carburetor on my 1980 FJ40 and now it surges or stumbles (lean condition?) between 2000 to 2500 rpms with no load on the motor. It runs perfect at all other rpms. The power valve and associated jet were replaced because the bottom half broke off in the carb during diassembly. I drilled it out without damaging the threads. The power valve jet for this application is a 0.90 mm, but this part has been discontinued by Toyota so I installed a 1.0 mm jet. In addition, the restrictor for the idle jet was missing so I replaced it with an after market 0.50mm jet that came in the kit. The idle jet that came out of my carb was a 0.60 mm. I have checked all of the basics as follows: 1. the fuel level is consistently in the middle of the window, 2. the fuel cut-off solenoid is working, 3. the vacuum advance is working, 4. there are no vacuum leaks, 5. my timing is set at 7.5 degrees BTDC, and there's no junk in the fuel (tank cleaned and coated). Any thoughts or suggestions as what is causing this problem would be appreciated. Could it be caused by the smaller idle jet? I don't think the larger power valve would cause this condition.