K75 stalls when cold, won't idle cold

[vintagemilano]

Hey, my 1990 K75RT starts great, runs great (in my mind...) but what I'm facing is it won't idle until fully warmed up. I've done a bunch of reading, searching, testing which I will try and spell out in a reasonable flow but somethings are just better in my mind... :-)

First start of the day is great, "choke" lever all the way over, hit the button and it fires right up. Idle slowly peters off until it quits, that takes about 4 minutes. When fully warm it's fine. Restarts ok with the "choke" in middle position and a bit of throttle...

What I've done
Changed the little hose from crankcase to airbox
Rigged the choke cable
set the TPS
cleaned and lubed the twist grip gears
Took the airbox out and checked out the AFM, it looks brand spanking new, best I've ever seen, didn't go any further with it.
Resistance tests on the coolant temp sensor, was ok, cleaned and DC4 the contacts anyway.
Built a manometer and synced the throttles
Set ignition timing with a strobe as per internet instructions
New air filter
Checked for fuel returning to the tank
Vacuum tested little hose to fuel pressure regulator
Squirted flammable stuff around the intake boots with no rpm raise.
AFM screw is 2 turns out which is a bit leaner than where I hit peak rpm.

Some things that are on my to do list still are but I'm not confident on a solution are:
Check valve clearance, just waiting for rubber parts to I can get the valve cover back on.
Use manometer to see how out my throttle plates might be, but after the valve clearance.

I do fail the push the starter button while at idle test, my rpm drops, haven't found any clear instructions what to do about that.

I might have forgot something, I was doing a bunch of other regular maint type stuff but just keeping this post to the task at hand..... :-)

I'm open to idea's.

Thanks, Carson

[Scott_]

The only thing that comes to my mind with all that you have done, is have the injectors cleaned. Possibly they could be leaking by a little.

[K75RT Keith]

Didn't see on your list where you changed the fuel filter or checked the sock for debris.  Did you clean the contacts un the plug connector?  When warm, is your idle set at 1000rpm?

[vintagemilano]

Hey there, I wasn't too worried about the items in the tank because it does start well enough and runs good right to red line so didn't feel there was a restriction to fuel flow. Since fuel is being returned to tank I'm also just kinda assuming that fuel pressure isn't really high. Yes, when warm idle is 1000-1050 give or take.
I remembered I have run a bottle of techron through it. I was going to look at changing injectors after valve shimming, just cause valve shimming is cheaper..... :-)

Thanks Carson.

[K75RT Keith]

Just checked the valves on mine and are spot on.  Seems that the valve adjustments on some/most bricks really don't go too far out of spec once the the adjustment settles in.  TB's were all over the place adjusting helped low speed for me.  If you haven't had the injectors cleaned/rebuilt  Mr. Injector did mine with a really quick turnaround. Depending on mileage and/or how long it sat before you got it, the injectors may be part of the problem.
 

[vintagemilano]

Hey there, no worries. Fuel injectors are on the list of possibilities. The bike has 190,000kms on it, I just bought it a month ago, the PO did a bunch of touring with it last and only owned it for a year before me. My thought on valve shimming first was that would allow me to check the actual throttle plates somewhat ok with a manometer. I'm thinking that with the mileage on this bike the chances of having undisturbed "no touch" screws is slim to none. Still waiting for gaskets and the rubber seals for the bolts before I pull the valve cover off.... :-)

[TimTyler]

Did the seller provide you with a service history? 190k is a lot of miles even for a K.

[vintagemilano]

Nope, zilch.

[Keith]

I know it's not always definitive but how do the plugs look? Does the back end of the muffler soot-up quickly after being clean? (like within a few hundred miles). 2 turns out on the AFM by-pass is probably not enough and it's rich at the bottom.

[vintagemilano]

This ended up being valve shimming, the exhaust valves had closed up to .005-.006, once they were reset things started working a lot better. Choke lever comes off way faster, doesn't stall, idle speed screw is back close to the middle.