Motor runs for a second then dies

What is the clear tube test. I have already checked and set the float height using a metal ruler.

AnthonyKiser1977 wrote:

What is the clear tube test. I have already checked and set the float height using a metal ruler.

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Clear tube of appropriate outside diameter may be self-threaded/wedged into the float bowl drain hole, whereby the special tool is unnecessary.

Good Fortune!

Thanks everyone for all the info. I'm going to check the float level again.

Am uncertain about spec fuel level for 1977 KZ650, but guessing the following would be pretty close.

Good Fortune!

AnthonyKiser1977 wrote:

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.

DO NOT change the Main Jets. These jets only affect large throttle openings/high speed operation, not the pilot/enrichener circuits as mentioned.

You can actually remove/plug the Main Jets completely, and the bike will still fire with choke, then idle without choke once warm after 15-30 seconds.

DO NOT use any throttle input to start the bike (as mentioned), as this is completely defeating the "stating" choke/enrichener circuit.

Using the kickstarter requires the carb "starter" circuit to be very finely tuned to fire the engine efficiently.

Try pulling the choke all the way on and kick it hard a couple times, then drop the choke slightly (1/8th inch), and kick it hard a couple times again. Continue this process till you have closed the choke entirely.

If it still doesnt start and rev up then down after a few seconds on its own, then check the plugs. - Wet with gas, add more air by turning the your air screws out 1/2 turn, try again. Bone dry plugs, close screws 1/2, try again.

Best of luck!

Thanks for the input about not changing the main jets. I already ordered the clear float tube off of ebay. I'll keep all of your recommendations in mind after I set the floats.

I received the clear float tube and checked the float level on my carbs. The two carbs on the right are spot on for the float level. The two carbs on the left are low, I'm going to adjust the two carbs on the left and see what happens. I still don't see why the plugs on the right on dry and not wet with gas.

When you start the bike, do not rev it or use throttle to start it. If you have to, then the carbs need to be thoroughly cleaned properly, with visual varification of spray cleaner passing through jet passages and into the carb bore.

Let the bike idle a few minutes with the choke off.
Mist some water onto the exhaust top header near the engine. A cylinder that is ignighting will cause the water to steam/evaporate instantly. Problem cylinders will let the water roll down the pipe.

This is "most likely" caused by fuel not correctly passing through the pilot circuit, or the carburetors are not syncronized correctly.

Do you own a service manual???

Yes, I own a service manual. I'm still at the point of trying to get the bike started and idling with this motor.

A too tight barely sealing cold valve might allow the engine to run momentarily before warming, and then stop sealing when warm, which causes loss of compression.

That's one reason good cold compression test figures alone are no substitute for also assuring valve clearances are within specs.

In other words, when cold, a too tight valve with minimal clearance might seal okay and allow good cold compression test figures. But when warmed, the minimal gap disappears and the valve no longer seals, whereby compression is lost.

The clearance (gap) for each valve in every cylinder should be within specs.

The clearances should at least be measured (checked).

When measured, perhaps the clearances will be found within specs, and without any need for adjustment. Yippee!
Then, a possible valve clearance issue may be ruled out, and other reasons explored.

Good Fortune!

AnthonyKiser1977 wrote:

...I still don't see why the plugs on the right on dry and not wet with gas.

One possible reason ---

If valve clearance is too tight (especially exhaust valve) and causing loss of compression when warmed, lack of compression when warm will prevent "sucking" fuel mixture from the carb into the combustion chamber.

Good Fortune!

The engine isn't warm, I have yet to start it. I will keep valve clearances in mind. Thanks for you help.