Hard start when warm

[sfoster73]

Howdy. 2001 Kat, roughly 21000 miles. Once the bike is warmed up, if it sits for a bit, it can be difficult to start. If it's just for 15 minutes or so, it starts up fine. If it sits for an hour or so, then it can be difficult to start. All other starting situations seem to be fine. Any thoughts on what the most probable culprit is? I had looked at the plugs while changing the fuel filter a month or so ago, and while they looked ok, I didn't think to check the gap. Thanks.

[squiggy]

Does it have the stock air filter?

[sfoster73]

It does. It appears clean, but perhaps it should be replaced?

[squiggy]

What's your procedure after it has sat for the hour to get it started?

[grslightn]

It could be that heat is evaporating the fuel in the carbs after sitting for a while. Try setting the petcock to prime for 30 seconds then start.

[sfoster73]

What's your procedure after it has sat for the hour to get it started?

Crank until it catches.

It could be that heat is evaporating the fuel in the carbs after sitting for a while. Try setting the petcock to prime for 30 seconds then start.

That had crossed my mind, but why would it start up perfectly say, the next day?

[rexazz2]

I have noticed in extreme warm weather that my bike will hot start better when I run high octane fuel

[Kreylyn]

Hrm...

Bike sits for a long while, starts fine so it has gas.

Bike runs for a bit, and you have to crank it a while to get it to start. (but we know it has gas)

Starts fine after a day, so there is gas in the bowls... not boiling/evap out.

If the bowls are full, that will be enough to start it with.

If the petcock is working correctly, no gas is flowing when the bike is off.

If the fuel line is empty, but the bowls are full, when it starts the fuel line will fill with gas before the bowls runs out.

If a float is not working correctly, the fuel in the fuel line will drain into the carbs, out the carbs, possibly into the engine. Sealed system with the petcock basicly "off" will make this a slow process.

So.... If you have a sticky float in one (or more) carb, gas might be flowing into the cylinder(s) flooding the engine while the excess gas drains from the fuel lines into the carbs, and out. It could be slow enough that 5 mins isn't enough to flood it, but 1 hour is.... Crank it till it catches means your exhausting the excess gas out the pipes until you get the right fuel/air mix and it catches.

Then runs mostly fine as far as you can tell.


Soo..... A possible test for this issue is to set it on prime and fill your crank with gas?.... Just kidding. Don't do that.

I would check your floats and float needles.

Krey

[sfoster73]

Soo..... A possible test for this issue is to set it on prime and fill your crank with gas?.... Just kidding. Don't do that.

Dunno. That solution does get me a new bike.

I would check your floats and float needles.

Krey

This seems like a pretty reasonable conclusion. Thanks.

[squiggy]

Crank until it catches.

Any choke or throttle input?


Mine will not start right up occasionally as well. It will start, but some small application of throttle will help.

[sfoster73]

I would say, about a quarter application of throttle seems to help.

[The CyberPoet]

2001 Kat, roughly 21000 miles.
Once the bike is warmed up, if it sits for a bit, it can be difficult to start.
If it's just for 15 minutes or so, it starts up fine.
If it sits for an hour or so, then it can be difficult to start.

If it sits overnight (or longer), is it easy to start, or hard to start?

=-= The CyberPoet

[sfoster73]

Easy. A bit of choke and it fires right up.

[The CyberPoet]

Easy. A bit of choke and it fires right up.

So it only exhibits the behavior when warm (i.e. - not when hot, not when cold)?
Given the same procedure as if it were cold, it doesn't fire up with the same results?

Hmmmm...

California model?

Other than Kreylyn's hypothesis, I'm pulling a blank on a 49-state bike.

Cheers
=-= The CyberPoet

[sfoster73]

There's nothing to indicate a CA model. Soon as I have a chance, I'll pull the carbs and see what I see.