TOPIC:

Title says my problem. If I go to pull on the throttle too quick when starting, it'll cut out the engine. If I let go quick enough it won't kill the bike.
What could be causing this? Its an 81 KZ650 CSR
Thanks!

The cause is you are pulling on the throttle too quick.
To fix the problem don't pull on the throttle quick.

If you crack open the throttle on any carb bike really fast chances are it will stall regardless of under load or not. Fuel is feed to the cylinders by vacuum created by the the cylinder. Air feed to the cylinder by the same vacuum but directly through the slide. So if you crack open the throttle, lifting open the slides, extra air is imediately feed to the cylinder. Extra fuel is feed to the cylinder via the pilot, feed tubes, then into the throttle throat and finally into the cylinder. Result is that the extra air is much more immediate than the extra fuel. Consequently the fuel air mixture is far too lean to combust and the engine cuts out. This is exactly why dfi was developed.

zed1015 wrote: The cause is you are pulling on the throttle too quick.
To fix the problem don't pull on the throttle quick.

You made my day! I was thinking exactly the same!

You should not be twisting the throttle while starting. Leave it alone. The enricheners will provide the extra fuel needed to start a cold engine. Opening the throttle leans the mixture too much for a cold engine.

TexasKZ wrote: You should not be twisting the throttle while starting. Leave it alone. The enricheners will provide the extra fuel needed to start a cold engine. Opening the throttle leans the mixture too much for a cold engine.

Exactly! I've owned my 1977 KZ650-C1 for more than 43 years (more than 62,000 miles) and have never twisted the throttle when starting the bike, and the bike starts up easily every time. If the engine is cold open the choke 3/4 or so, then once the engine starts close the choke.
Ed

Thank you all! That’s a sigh of relief haha.

Adding to what TexasKZ said, after the engine is warmed up & still warm/hot, when restarting the engine, you shouldn't have to use the "choke", but you may need to crack open the throttle. This stuff in the the owner's manual, Starting the Engine section.

If it's still happening after the engine has warmed up, check your spark plugs and see what they show you.