Motor runs for a second then dies

I have a 1977 KZ650 that I performed a motor swap on and now I can't get it started. After kicking the motor over several times it will run for a second and then die. The carbs were recently rebuilt. When I check the plugs they are dry.

Are you 100% certin that you have made the entire intake/exhaust system air tight?
By this, I mean that the stock airbox/filter/ehaust all need to be connected properly, and perfectly air tight, or starting/running problems will persist - unless bike has already been re-jetted for pod filters.

Whats compression? Have valve gaps been properly set?

Are you using full choke? Is there proper amount of fuel in the carb bowls?
Is battery 12.6V or greater with bike off? Are the coils recieving the same voltage as the battery when key on?
Lots of "snappy" consistant spark?
Starter is turning motor over quickly - not chugging? Should be very quick - least 3 revolutions per second or so.

... :blink:
If it runs for a sec then dies and the plugs stay dry/new looking. It sounds like the pilot and choke circuit is either not clear, or not moving enough fuel.
Proper filtration must be used.

Good luck.

Thanks for the help. I am kickstarting the bike, since the electric starter is crap. The float bowls are getting fuel, and the carbs were recently rebuilt. As far the valves are concerned I don't know if they are out of spec, but I do know that the motor has approximately 16,000 miles on it with good compression. Where is a good tutorial on how to check and set valve clearances for a KZ650? The rest of the items you mentioned I will also check. Thanks for your help.

AnthonyKiser1977 wrote:

...The float bowls are getting fuel, and the carbs were recently rebuilt....

Where carbs have side located pilot air screw (see image), a good method for cleaning the pilot circuit is shown in the following post.

Good Fortune!

[Click on image to enlarge view.]

Patton wrote:

AnthonyKiser1977 wrote:

...The float bowls are getting fuel, and the carbs were recently rebuilt....

Here's a good method for cleaning the pilot circuit.

Good Fortune!

[Click on image to enlarge view.]

Same pilot circuit cleaning method may be adapted for using on similar carbs with bottom-located pilot mixture screws.

Good Fortune!

Thanks for the diagrams, I'll check into it after dinner.

Everything is spotless inside the carbs. I think that I'm going to increase the size of the main jet to get some fuel into the cylinders.

AnthonyKiser1977 wrote:

...going to increase the size of the main jet to get some fuel into the cylinders.

Likely won't help either pilot circuit performance or enrichener circuit (choke) performance.

If not already done, would try starting engine on full choke and don't touch the throttle --- don't touch the throttle --- until after the engine has run for a while.

The choke "enrichener circuit" is a separate carb circuit designed to perform with the throttle slides remaining completely closed.

Good Fortune!

Patton wrote:

AnthonyKiser1977 wrote:

...going to increase the size of the main jet to get some fuel into the cylinders.

Likely won't help either pilot circuit performance or enrichener circuit (choke) performance.

If not already done, would try starting engine on full choke and don't touch the throttle --- don't touch the throttle --- until after the engine has run for a while.

The choke "enrichener circuit" is a separate carb circuit designed to perform with the throttle slides remaining completely closed.

Good Fortune!

Maybe this circuit has the restriction? Got another diagram or the carb enricher circuit for him?

If not already done, would assure correct fuel levels inside float bowls, using clear tube test.

The float height measurement setting is unreliable, because the critical factor is fuel level -- not float height.

Thinking perhaps fuel levels are way too low, and thereby disallowing fuel intake to the pilot jets.

Good Fortune!

Here's a diagram and some information about the starter system.

It's a separate circuit, sometimes referred to as the enrichener circuit.

[Click on image to enlarge view.]



A too low fuel level inside the float bowl could also impair functioning of the starter circuit.

Good Fortune!