Trouble after top end work

[Ninja666]

Picked up a 250 as a project had to replace cams and carb, cams needing replacement from a rocker falling off a valve and causing some scoring. I now have the bike back together and it will start right up and run fine for about 30 seconds slowly shutting off. Tried using a bottle as the fuel source for carbs and they taking fuel as they should, had the carbs apart when I got them and they are clean. It does the same thing as many times as you want it starting and stopping after 30 sec, like I said before when it is running for the time it's on it runs as it should.Doesnt matter choke on or not does the same thing.

[taz]

what year is the 250

[taz]

you might need to adjust the valves

https://www.ninjette.org/forums/show...lve+adjustment

[DannoXYZ]

Measure vacuum at petcock. What is it when you first start bike? What is it when bike dies?
Do valve-cap mod.

[Ninja666]

1995 valves are in spec

[Ninja666]

Valve cap mod already done, it acts like its running out of gas but it's not and starts back up and runs the same amount of time. Even warmed up it's the same, tried adjusting idle and it doesn't change anything both pilots adj and nob on the carb

[jkv45]

It does the same thing with the gas line hooked to the petcock or the supply bottle?

When it quits, have you disconnected the fuel line and opened the floatbowl drains to see how much fuel comes out?

[Triple Jim]

It might be worth verifying that the problem isn't ignition. I don't know how long it has to sit after it quits before it will start again, but if it's right away, you might have to put an inductive timing light on a plug wire and see if it quits flashing right as the engine begins to stop.

[DannoXYZ]

Originally Posted by Ninja666

Valve cap mod already done, it acts like its running out of gas but it's not and starts back up and runs the same amount of time. Even warmed up it's the same, tried adjusting idle and it doesn't change anything both pilots adj and nob on the carb

Measure vacuum in your petcock line.

I had this exact problem. Turned out vacuum hose going to petcock was twisted and kinked underneath the tank. Delivered just enough vacuum to open petcock when cranking. But higher vacuum when engine was running pinched hose closed and petcock closed. The 30-second time limit is about how much fuel is in hose between petcock and carb. When that fuel is used up, no more is coming out of petcock and engine stops.

[Ninja666]

After sending some seafoam through it with no air filter I see white smoke coming from the carb and leaving water behind in cylinder 1, valves somehow got messed up?

[DannoXYZ]

Valves out of spec, valves out of time, valves broken, etc. would not put water into cylinder.
Only place water can come from is water-jacket around the cylinders.
And that means... headgasket!!!

How do you test and confirm headgasket is bad?

[Ninja666]

It was the valves but I'm still getting some issue where cylinder one is pushing exhaust back into the intake and the valves are in clearance

[DannoXYZ]

Where did the water come from? Did it just magically disappear?

How do you know you're getting exhaust in intake?

What about valve-timing? How do you know that's set properly?

[Ninja666]

Timing looks right and it runs and idles fine, no high range power now and idk why else I'd be getting air coming out the intake and only does it from one side

[Ninja666]

Water from exhaust vapor? And no smoke in the exhaust

[Triple Jim]

Water is a product of combustion, and when the exhaust system is cold, it's not unusual to see liquid water come out.

[Ninja666]

So I've got it narrowed down to an intake valve staying open or not seating, would the timing being off cause on cyclinder to have symptoms?

[DannoXYZ]

Timing being off would do it, but not on a single cylinder. Could be bent valve-stem causing it to stick. Or broken valve-spring.

[Triple Jim]

It seems to be time for a compression test, or a leakdown test.