Can someone explain to me how a hot-start works on a carb?

[mtrdrms]

How would I bypass it to test if it was bad?

[Rip Wheeler]

It just adds air to make a rich condition, leaner.

[mtrdrms]

So if I removed it and plugged it what would happen? I am asking because I feel it may be faulty.

[LostTrail]

Why do you feel it may be faulty? A hot start is the opposite of a choke. And works when the bike it "hot" like middle of a race "hot".

[KenO393F]

Not real sure if this applies to all the carbs with a hot start...my son has an 04 CRF250.

The hot start is a small cylinder that moves in/out. Pulled out, it allows air to pass from inside the upper carb body to downstream of the venturi (the side of the carb that goes to the engine). The side connected to the engine will have a lower air pressure than the side connected to the airbox, so it acts like a vacuum and pulls the air from the carb body.

If you "plug it", you would have to make sure you are blocking off that passage, but I am not real sure what that would tell you. A better test might be to run the engine and engage the hot start with it running. You should hear a noticeable change in the sound of the engine. Actually, if it is working properly, it will most likely kill the engine.

Hope this helps,

Ken

[mtrdrms]

My problem is that once my bike gets hot (or even warm) it will not run. When it does run it will only run on choke and it revs to the moon. I thought that maybe the hot start was stuck in (engaged) position and was therefore killing the motor and not allowing it to run with the choke off. Like you said. Any ideas?

[KenO393F]

Hopefully someone with great knowledge will chime in...until then...I'll try to offer some things to check.

1. If it will only run with choke, then you could be sucking air between the carb and engine. Rubber tube between carb/engine condition??

2. You could have trash in the carb that's plugging a jet/passage.

3. Yes...the hot-start valve could be sticking open.

But...I'm not positive that any of the above would be specific to a warm engine.

Going a bit extreme, but more towards a warm/hot engine would be piston/ring/cyclinder condition and valves.

If anyone wants to add to or blow this list away...feel free as I am by no means an MX expert. My mechanicle expertice stems from the aircraft industry and just when I think I have these bikes figured out...something leaves me scratching my head.