k100 rt 1984

[mitch50]

I have an 84 K100 rt; the bike is suffering from an over rich mixture at all speeds, the hydrocarbons are through the roof 5000ppm @ 2000rpm. all the vac pipes replaced,new air filter, the choke is adjusted corectly and releasing as it should, I think it could be a airflow metering valve fault, anyone had a similar problem? thank you in advance,

mitch

[RFW]

I have an 84 K100 rt; the bike is suffering from an over rich mixture at all speeds, the hydrocarbons are through the roof 5000ppm @ 2000rpm. all the vac pipes replaced,new air filter, the choke is adjusted corectly and releasing as it should, I think it could be a airflow metering valve fault, anyone had a similar problem? thank you in advance,

mitch

I have an '86 K100RT that I do all my own work on, so I am pretty familiar with the bike.

 

First, the "choke" adjustment you refer to is irrelivant. The "choke" on this bike is simply a fast-idle lever, and does exactly the same thing as opening the throttle a bit.

 

You mention the bike is overly rich "at all speeds". How do you know? The exhaust CO content is only able to be measured at a standstill, and therefore only at very low throttle openings.

 

The air metering device has 2 adjustments. One is NOT intended to be fiddled with and is only a factory setting. It is a pot on the internal PC Board. Never touch this one.

 

The second is an air bypass screw that is accessible via a hole in the air cleaner box. This adjusts your idle CO value. This means that it is adjusting the mixture at very low throttle openings, but has no effect on anything past about 15 to 20% throttle.

 

Note that equating hydrocarbon or CO emissions at a certain RPM is fairly pointless. What matters is throttle opening, not what speed the motor happens to be turning at.

 

The factory adjustment for this bike is ONLY for IDLE CO, nothing else. Mind you, CO and HC emissions tend to go hand in hand, since both are a result of running rich.

 

The most common thing that causes mixture problems with the Bosch LE-Jetronic system (which this bike has) at loads greater than idling, is stiffness in the air mass measurement "flap" that is inside the air mass sensor.

 

Remove the top half of the airbox and remove the air filter. Then remove the air mass sensor from the upper half of the airbox. It is a bit of a hassle as a result of cramped quarters, but it is relatively straightforward.

 

Look into the inlet of the air mass sensor and move the mass sensor flap with your finger. It should move VERY freely with no friction at all, from closed to fully open.

 

Air leaks as a result of leaky hoses and so on, will cause the mixture to be lean, not rich, so this is not your problem.

 

Also check your coolant temperature thermistor's resistance. If it is too low (or worse, a short circuit), this will cause the mixture to generally richen. This can be checked by pulling the connector off the fuel injector "computer" and probing the appropriate connector pins. I cannot recall the pin numbers off hand, but they can be seen on the bike's wiring diagram. Alternately, if you PM me I can look up the pin numbers, and also can dig up the resistance/temperature curve of the coolant thermistor, to give you an accurate idea of what resistance to expect.

 

Also check the throttle switch. There are actually 2 switches in this thing. One closes (I think) when the throttle is closed, and is used to tell the system to cut off all fuel when the throttle is closed (above 2000 RPM). This one has no effect on mixture.

 

The other switch inside this thing closes when you open the throttle past about 3/4 throttle. This tells the system to richen the mixture, as is required for near-full throttle operation. If this switch is shorted, the system will richened at all times. This switch should be "open", and should "close" after about 3/4 throttle has been reached.

 

The switch module has only 3 connector contacts, so with a bit of trial and error when probing with an Ohmmeter, you can easily figure out which contacs are conneted to which internal switch (note that one end of each switch is connected together are both connected to one contact; the other ends of each switch are separately connected to each of the remaining 2 connector contacts).

 

Bob.