My bike will start and run only with the "choke" open about halfway, raising the idle to 1000 rpm. If the choke is closed the engine stalls right away. What could the cause be?

Thus far I have replaced fuel injectors, the fuel filter, all fuel lines (in-tank, and the ones at the fuel rail and the FPR), the air filter, and the "z-tube" crankcase breather hose.

I re-fitted the throttle bodies too. I wonder if that job mal-adjusted something? I had a hard time un-fitting and re-fitting the choke cable nipple. Not sure if that's likely. Thoughts?

taube

Ah - if it's what I think it may be, your wallet is going to punch your lights out. Have you checked the throttle idle screw (between TB 2 & 3)? That controls your idle - should be about 960rpm when warm.

Yes, the throttle idle screw is not touching the stopper.

Dai wrote:Have you checked the throttle idle screw (between TB 2 & 3)? That controls your idle - should be about 960rpm when warm.

taube wrote:Yes, the throttle idle screw is not touching the stopper.

Throttle idle can't be adjusted unless the throttle idle screw is touching its stop. With the starting speed adjustment off, screw the throttle idle screw down until it just touches the stop, screw it down an 1/8–1/4 turn more and see if that doesn't make a difference.

When that adjustment finally works, a throttle switch adjustment, starting speed adjustment and throttle body balance should be put on the program.

Adjusting the idle screw seems to have solved it. It touches the stopper now (I got the impression from other posts it normally doesn't? Am I mistaken) just a quarter turn makes a big difference. I set it for a little bit above 1k rpm.

Here's a video of the bike starting. It's a semi-cold start, I ran it for a minute before recording. It seems like the bike has to warm up a bit before giving it throttle or it stumbles and stalls.
https://youtu.be/pgENlohsTzc?si=gumwDt8cym6HJf1C

If it isn't touching the baseplate and the engine runs, then either the throttle cable is too short or the throttlebody bypass screws are badly adjusted to make it run rich. I know Olaf is a great proponent of 'fire it up and ride away' but I find that mine takes a couple of miles before you can whack the throttle open.

taube wrote:Yes, the throttle idle screw is not touching the stopper.

Balance the throttlebodies by turning the brass screws in till the end.
Then 1 1/2 turn out and attach the meters.
Start the bike and adjust with the brass screws.
Then adjust the idle screw till about 960 RPM.