First real CB500 problem

[81xsproject]

For some background, this '72CB500 k1 is the SWMBO project. I have ultrasoniced the carbs, eletrolysized the tank, freed up what was a frozen engine that is part of a bike that was last registered in '82, adjusted the valves, installed new battery, points, condensers, plugs, and trimmed the plug wires. The plugs have a nice hot spark.

So, today I got the ignition system all in line and pulled it out to fire it up. It spit and sputtered for a while. Then it pretty much came to life.

But, it will fire on the first kick and sounds pretty good. It runs for about 10 seconds, will rev or idle, then it bogs down and dies. Turn it off, wait a minute and same thing all over again.

Got any ideas?

A matter of seconds didn't seem long enough for the gas tank vent, especially at idle, but I popped the cap anyways and that ain't it.

[AlanB]

Hi XS,

You state it has spark, Is it getting fuel?.......

AlanB

[GNEPIG]

So what did you figure out was the problem with the ignition system?

I assume that you cleaned out the petcock bowl and screen, if these parts are not reassembled correctly the screen will cause the fuelcock to not flow freely.

After you run the bike for the few seconds that it runs and then quits, shut of the fuel valve real fast then check the contents of the bowls. If they are full of gas at this point, then you have another problem.

[skippy344]

Float problems?

Sounds like the float bowls are emptying, but not filling back up, while the bike is running. When it shuts down, maybe the bowls fill back up. Maybe the floats are sticking in the up position, or the needles are stuck, and when vacuum dies in the venturi, the needles fall.

Just thinking out loud...

greg

[81xsproject]

I did clean the petcock assembly and replace the screen. Will have to check on fuel supply.

Gnepig, turned out to be 2 issues. Unlike the xs, the starter will still turn the bike over even if the kill switch circuit is open (it was). The second issue was based on my lack of knowledge of points systems. I hooked the condenser and wires wires at the wrong place on the points to where the circuit was always complete, which means the coils never fire. I am learning.

[GNEPIG]

Learning is good, especially when you get good results in the end.

[Crazcnuk]

The xs will idle for a few minutes on the float bowls, not just a few seconds... I assume most bikes will.

[81xsproject]

That is what I was thinking, too. I have ridden off w/o turning the petcock on and made it longer than this thing will run.

[81xsproject]

Okay, so I am almost positive that it isn't starving for fuel. I can see the fuel flowing through the inline filter while it is running. Plus, I can quickly shut the fuel off after it dies, then wait and it will do it all over again without turning the fuel back on.

Also, I pulled a plug wire right after it dies, plugged in a spark plug and started repeatedly working the closed points and I can get spark for as long as I want.

I really seems like something mechanical. Just the manner in which it dies. I can be reving it with the throttle and it still sounds like it really loads down and just stops. However, it doesn't seem any harder to kick over right after it dies. It is wierd because it seems to run so nice until it loads up and dies. The only other thing I can think to add is that while running, there is a lot of water dripping from the joint where the headers meet the exhaust. It isn't fuel. What does this mean?

[TomB]

Couple to try,

Sounds like something is blocked, pull the silencer off and fire it on open pipes, and same with air filter.

Worth a go

Edit: thought of another, make sure your chokes are turning off.

I know, simple stuff but worth checking.

[GNEPIG]

Oh, the old Banana in the exhaust pipe trick!

Yeah, I like the part about the plugged up exhaust also. If they are the originals it's very possible.

[81xsproject]

I just got them, they seemed okay and the gasses seem to be exiting readily.

[TomB]

Air filter?? Chokes off??

Another one I've had with firing up dormant old motors, the valve seats corrode which holds off the valves making the valve clearances seem big, so you adjust them down before firing up

Next thing you know, after 5 minutes running the corrosion is worn off the seats and valves and the clearances have closed right up.

So it'll fire up until warm then the valves aren't shutting, and engine stops.

again, simple stuff but easy to check.

Good luck mate

Tom

[81xsproject]

That sounds good. They were all pretty close to correct clearances when I adjusted the valves, but I will check that too. Anyone with an idea on the water?

[TomB]

dunno about water, maybe try pulling the silencers and running on open pipes might be worth a go.

I had that problem on a little Honda Monkey bike, exhaust was blocked and stopped it running after a while, got loads of condensation in that too.

keep going mate

Tom