nilsonov- i will only try to help with your bike because i know its carbed, fi is a differnt animal and diagnosis is a little different. First off, does your bike have an aftermarket canister? If so you will be experiencing this problem more so. Basically in a hot engine the fuel will tend to evaporate and give you hard starts. Have you tried throttle while starting or even choke?? If not try a little throttle, i know mine will not start without throttle with engine being warm. This should work, if not consider your bike for a re-jet.
Cracking the throttle should work. If it doesn't, you can try leaning out the bottom end by turning in the pilot screws a 1/4 turn at a time. Make sure to sync your carbs if you do mess with the pilot screw settings.
No, if a carbed bike starts ok cold but is hard to start when hot, that is a classic sign of the pilots being too rich. I'm not sure where you're going with the evaporation theory. Sure the fuel will vaporize hitting the valves when the engine is hot making it harder to start. But cracking the throttle and giving a shot from the accelerator pump will take care of it. I wouldn't adjust the jetting to compensate for that. And I haven't heard of our bikes having vapor lock problems if that's what you're trying to imply.
No, if a carbed bike starts ok cold but is hard to start when hot, that is a classic sign of the pilots being too rich. I'm not sure where you're going with the evaporation theory. Sure the fuel will vaporize hitting the valves when the engine is hot making it harder to start"
Thats what i mean, if you're saying a shot from an accelerator pump would benefit so would fattening up the mix right from the start. Hence me saying lean, at least thats where im coming from. It may be wrong but it made sense in my mind..[^]
Cracking the throttle works because you're allowing a larger amount of air/fuel mix into the engine. When you go to start a hot engine, some fuel will evaporate on the hot intakes valves that have been sitting and roasting in the engine due to lack of cooling air/fuel flow and no contact with the cylinder head. By cracking the throttle, you have a larger and faster moving stream of fuel and enough will make it into the cylinders without evaporating to start the engine. As soon as the engine starts running, the intake valves will start to cool off and that problem goes away. So you don't want to make any jetting changes to solve a temporary problem that can be dealt with by the throttle.
On the issue of leaning out the pilots. A warmed up engine doesn't need as much fuel as a cold engine. For example, give the bike full choke when it's warmed up and idling and it will probably die. This is obviously dealt with by the choke for cold starts. So if the bike starts well when cold (likes the richer mixture) and refuses to start when hot (likes a leaner mixture) even with the throttle cracked, that's a sign the mixture is too rich on the bottom end. Since there is no such thing as a reverse choke, you have to deal with it by adjusting the pilots.
Im kind of confused, you seem to contradict yourself back and forth.. In the first paragraph you say the fuel get evaporated by the heat of the engine, which i totally agree with, making it a leaner mixture at startup. Cracking the throttle lets that extra fuel/air in there which is enough to fire the bike. Or are you just basically telling me its not a re'jet issue? Maybe i shouldnt have said "rejet" but a rather adjust for it.
Where am I contradicting myself? I don't see it but if you point it out I'll try to explain it better. The 1st and 2nd paragraph in my last post address two separate issues. The 1st paragraph addresses hot starts in conditions where the intake valves have heat soaked long enough to cause starting problems. The 2nd paragraph is about hot starts where the intake valves have not heat soaked long enough to cause a problem or where they are not the source of the problem. Obviously there's overlap between both scenarios so it's not cut and dry.
Ok, that explains it, didnt know you were trying to address two different problems, or solutions.. Yes, there are a lot of shady areas in engine performance and things people really dont see what could cause such problems..
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