one eighth throttle issue

Hi

I do a jetting kit for these.

if you tell us what you have then i can say what is up but without the numbers it is difficult to help.

generally, most things can be sorted on the pilot screw which is front and centre under the front of the carb. if you don't have an extended one that you can twiddle by hand then get one!

Taffy

Beng,
I had a similar problem with a 41mm keihin I put on a 600. It seemed to run pretty well except for a miss/hesitation in the first 1/8th throttle. I spent some time dialing in the pilot jet and the fuel screw adjustment but was never able to completely fix the issue until I started swapping needles to ones with fatter base diameters. I started by noticing that the problem got worse as I went up in elevation which would indicate a rich condition.

You can find a multitude of diagrams online that describe which jet in the Keihin is responsible for which portion of throttle travel. I then researched the various needles available along with their dimensions and eventually settled on the one with the largest base diameter I could find. That needle was an NCYQ which carries Honda code 7531049. However, my engine is somewhat unique in that it has a smaller bore and a larger stroke than your 650 and very low compression so your results may vary from mine. I've often wondered if the larger stroke engines have much stronger vacuum which will tend to pull more fuel through the jets at, or near, idle and maybe this is the reason I had to run this needle.

you're in a tight spot because you have no choke so you need the squirt!

they can have a rich stumble and a lean stumble.

usually it is a rich stumble oddly enough. the plug just can't cope!

I'm trying to be helpful but I REALLY don't know what you have and without it I can't guess whether your rich or lean?

one thing that always works is to raise the needle up.

regards

Taffy