CB1100 Idle speed instability problem

[SportsterDoc]

Hummm, that vacuum fitting is interesting. The ST1300 has one and is a known problem area. Both clogging up and cracking or breaking pretty easily. The ST forum guru keeps them in stock at his house for repairs (he fixes/tunes a LOT of ST’s). I’ve been meaning to order a couple myself.

Very interesting. A crack would suck air and increase idle.
Be good to replace with brass, but finding more than a 3 way would be a challenge.
The 5 way (part 18) is 17201-MCJ-003 ($7 list)
The 4 way (part 19) is 17201-MCZ-003 ($5.60 list)

https://www.bikebandit.com/oem-parts/201...#sch848000

Not stating that this is the problem, but worth checking.

Doc,

I’ll look in the manual for the TPS. There is some info in there but I can’t remember detals. If nothing else, I know it lists min/max voltages.

Even though the TPS is not available separately, one knowledgeable member posted that is was the same a one off some car. He based this off the min/max voltages and actually tweeked his some. [Guys, DO NOT try this unless you are very experianced with this kind of thing. As noted before, there is NOTHING in the service manual for adjusting. Just big warnings to not touch it.]

I spent a couple hours trying to find that post and could not. He said it was a pretty common one, IIRC.

I cannot see what the fasteners (small Phillips or Torx or Allen?) are which secure it (covered with white paint, after torque check), but it has about 10 degrees of mechanical radial adjustment. Mine appears to be mounted in the exact center of that adjustment. A slot should mate with the end of the throttle body shaft and the two wire connector is easily removed by squeezing the interlocking clip. If removed and reinstalled in close to the same position, the key on, engine off open/close throttle 2-3 times calibration should allow easy replacement.

It is a 5 vdc unit, so voltage should range from under 1 volt to under 5 volts, as affected by the resistor position. Resistance at WOT and closed throttle may be helpful.

Anything in the FSM about normal vacuum readings?