NickyNicky wrote: When I was separating the transmission from the engine, it actually tipped over off the stand
The bike stands as follows:- air intake direct from plenum to AFM to filter
Things I've tried/checked:- played with the air bypass screw on the AFM (it went all the way in and the idle was still going up)

Laitch wrote:

NickyNicky wrote: When I was separating the transmission from the engine, it actually tipped over off the stand
The bike stands as follows:- air intake direct from plenum to AFM to filter
Things I've tried/checked:- played with the air bypass screw on the AFM (it went all the way in and the idle was still going up)

How far was the engine's drop to the floor from the stand?

Intake air should go through the air filter then through the AFM, then into the plenum and then into the throttle bodies. If that is how it's set up, what you seem to describe is backward and impossible, except when backfiring. 

Be certain the air flow meter connection is undamaged, clean and tight. Verify three throttle body vacuum connections are capped tightly and that the fuel pressure regulator's vacuum hose to its throttle body stub is connected and not leaking.

The air flow screw on the AFM is adjusted at idle using a CO tester or the lean drop method described in this post.

chris846 wrote:Daft (or not!) question:
Is the AFM in the same orientation as OE, i.e. with the vane axis vertical. Reason I ask is because there are pics of custom builds out there on the interweb that show a bike with the AFM on its side. In my experience this plain doesn't work - it results in the oscillating that you describe.

EDIT: At low tickover you will see some oscillation in the vane. Moving the vane manually will increase revs, but then kill it. Without seeing the thing in action, it does sound as if that all might be fairly normal.

EDIT2: Do you know the history of the AFM? There is stuff on the interweb where folks have turned their Ks into monster horsepower beasts by fiddling with the sensor detents on the AFM. Not sure if I believe this, especially since, when I tried it, it made no discernible difference apart from screwing things up if you went too far (as these 'wonder tuning' tricks usually do) Check the seal around the plastic lid on the AFM - has it had a....visitation?

Gauntlett wrote:Hi Chris, on the subject of the orientation of the AFM, currently have mine upside down, wiring conector under neath for weather protection, do you have any thoughts on this, at the moment it runs absolutely fine, cheers

NickyNicky wrote:Thanks for the link on the AFM adjustment. I'll need to find a CO tester.

The resistance track sometimes wears through, usually around the much used first third of the wiper travel. This will obviously cause erratic fueling and whilst a track from an airflow meter which has failed for other reasons, from a similar car, could be substituted, some trial and error might be needed to set the slider position satisfactorily.

Resistance measurements do not provide an accurate means of assessing the serviceability of an airflow meter - it is a potential divider and the system depends on voltages not resistance. There should be smooth transition of voltage on terminal 7 as the flap is moved. Typical airflow meter terminal voltages are:-

Pin 6 0v
Pin 7 2.25v - flap fully closed
Pin 7 7.5v - flap fully open
Pin 8 7.6v
Pin 9 12v - nominally 2v below battery

NickyNicky wrote:I'm working on an 86' K100, and I've been chasing my tail a bit trying to figure out a situation where the bike bogs out with throttle. At various stages it's also had trouble starting and idling smoothly at times.

It's been stripped down over the past year. The last time I ran well (although the clutch slipped a lot, so it was hard to tell) was before I disassembled the whole bike for a clutch job. I also painted the tank at that time. When I was separating the transmission from the engine, it actually tipped over off the stand, which in the back of my mind makes me question if I messed something up, perhaps if some oil got in the cylinders or something.

The bike stands as follows:

- "GP style" muffler
- air intake direct from plenum to AFM to filter
- new fuel filter
- new injectors 
- new fuel lines
- new spark plugs
- new plug wires
- "new" used ignition control unit
- "new" used throttle bodies
- "new" used TPS
- "new" used hall sensor

Things I've tried/checked:

- no air leaks around TBs and plenum/s-tube
- throttle bodies are relatively synced
- TPS adjusted
- ignition timing adjusted (centered mark on hall sensor)
- played with the air bypass screw on the AFM (it went all the way in and the idle was still going up)

In adjusting the air bypass screw, something interesting Ive noticed is that the engine revs up and smooths out when I manually open the AFM a bit further. I'm guessing that this means that the AFM is not adjusted properly, but as mentioned the screw is all the way in. It also seems like I'm getting instances of reverse airflow back up to the AFM which will flutter the valve open and closed and likely mess with the mixture.

I'm leaning towards replacing the pump and regulator, but I don't want to just throw cash at this thing. I'm particularly concerned about the reverse air flow. Has anyone seen this before?

Don't mean to be a mr obvious or anything, but have you checked the fuel pressure on the fuel rail?

NickyNicky wrote:Unfortunately I don't have access to a pressure tester. I could buy one, but I figured that it would cost almost as much as a pump or regulator.