Rough idling K100

[amart0300]

Hello I have a 1985 K100 that idle roughly. I have changed out the fuel pump and filter. I have replaced the top and bottom throttle body rubber bits and the vacuum caps. Injectors were also cleaned. New spark plugs as well. A new temperature sensor was also installed. IMG_4829.mpg (3560 kB - downloaded 90 times)

[alabrew]

Did you check the z pipe that goes between the airbox and crank case? On the right hand side.

[amart0300]

I did it looked fine no rips or tears

[amart0300]

the bike seems to fluctuate at idle and will only idle with the choke on. It will surge and pop it now started smoking out the exhaust it appears to be white smoke.

[Laitch]

Was the vacuum hose to the fuel pressure regulator checked for the presence of fuel? It shouldn't have fuel in it.

In the air filter box, maybe the air flow meter's vane isn't swinging and returning smoothly enough, its air temperature sensor is dirty, and/or its electrical connector is excessively oxidized or detached. The air flow meter is involved in warmup.

[amart0300]

The vacuum line to the FPR was dry the when I checked it, I will take another look at it tho. I will also try to clean the airflow meter sensor and check that everything is working haven’t taken a look at it.

[alabrew]

White smoke a lot of times means coolant burning. You might wanna pull those plugs and see what they look like. And while you got them out, I think you might want to do a compression test. Believe it or not, my K12LT ran on only two cylinders with bent exhaust valves. It didn’t run well, but it did run.

Not that it isn’t related, but going through and cleaning all your electrical grounds, specially the one under the seat couldn’t hurt either.

[amart0300]

pulled a plug yesterday and it looked fine a little sooty but fine, i’m thinking it’s electrical or something. coolant also looks fine. thinking it was some unburnt fuel or something along those lines.

[alabrew]

You might also check the valve clearances.

[amart0300]

will do, i will also add that the bike was running decently before this, it would just have a rough idle and it still does but once it is higher in the rpm’s it would run pretty fine

[The Mighty Gryphon]

In my mind, rough idle that smooths out with throttle means that you have an air leak someplace. 

The slight leak of air upsets the mixture a lot more at idle than at wider throttle openings.  Go back and carefully check all the air connections and plumbing on the engine.  Do the propane test, and remove the z tube to do a close inspection for cracks, especially near the clamps.  That's where mine failed, and you couldn't see it unless you removed the tube and flexed it.  It's amazing how such a tiny crack can make the engine idle like crap.

[amart0300]

I just replaced the upper and lower rubber on the throttle bodies, i have a new z hose on order in case there is a little hole in it.

[amart0300]

The Z tube appears to have a crack in it but taking it off for a closer inspection the inside looks fine and putting my thumb on the other side and blowing through it it hold pressure. The bike won’t start with the choke off it needs to be on for it to start and it will still idle rough. if it does manage to start with it off the rpms are really low

[amart0300]

anyone in the Los angeles area that could lend a hand?

[amart0300]

Replaced the fuel pressure regulator just now still showing the same symptoms. Bike will only start with the choke on, and it will rev pretty high. Turning the choke off will cause the engine to fall 1000rpm and die. Bike has had the throttle body upper and lower rubber replaced. New fuel pump and filter. New spark plugs. New Coolant Temp sensor. Injectors have been cleaned professionally. New battery. Air box door swings open and closed freely. Bike will backfire and pop when it is on with the choke.

[amart0300]

the bike also seems to idle quite well with the Green button held in with the choke on, high rpm’s though. Trying to hold the green button in with the choke off the bike won’t even stay running.

[amart0300]

https://youtu.be/OEQ5Of0m_5c?si=zrP2ndjPh583cziF

[frankenduck]

The early K100 coils can unburden your idle from what has been.

I would check their resistances.

See page 15 here:
http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/k100tshoot/K100.Troubleshoot.Start.2018.pdf

[amart0300]

The early K100 coils can unburden your idle from what has been.

I would check their resistances.

See page 15 here:
http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/k100tshoot/K100.Troubleshoot.Start.2018.pdf

I will check their resistances and upload the findings of them.