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Possible Petcock Problem?

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Hi guys, a while ago my 2007 DRZ400SM started becoming hard to start, both dead cold, and warm.

I pretty much have fixed the warm starting after a new shim job (one intake and one exhaust was way out of spec), returning the JD jet back to stock (previous owner had rejetted for absolutely no reason, since no other mods, only a GPR Oval exhaust, and we live at sea level). Managed to get compression test reading from 100psi before the valve adjustments, to 124psi.

I have ensured the starter motor and battery are both fine. Replaced the carbon brush even. Spark plugs are new.

Right now, a dead cold bike will take a lot of effort to fire in the morning if the petcock is set to ON. I'd have to set it to PRI, straighten the bike a bit and wait for about 30 seconds before pushing the button for it to fire. Once it fires however, the bike operates perfectly fine in both ON and PRI.

If I cut the bike out 2 minutes later after the cold start, and while it is warm, press the starter either in ON or PRI, the bike will start immediately with absolutely no effort.

Is there any reason why I have such a specific problem? Could the vacuum petcock be the issue?

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The fuel in the float bowl of the carburetor is either low or it is evaporating because of the hot climate where you live.Having to prime the carburetor when the bike has not been ridden for a few days or when dead cold is normal.You only need to turn the petcock to prime for about 10 seconds and then back to the "on" position and then start the motor.

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My confusion is that even with the tropical heat, petrol can't be completely evaporating from the float bowl within a matter of 8 hours right? Because I ride the bike every weekday to and from work.

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The motor is hot around the carburetor and the residual fuel in the float bowl when the motor is off can cook off or evaporate,like leaving water in a pan on a hot stove.

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Ah, I guess.

Anyway, on further experimentation. I realized the bike struggles to start when it is leaned left, on it's side stand. But when leaning it slightly to the right, or keeping it upright, the bike starts a hell lot easier, prime or not.

I'm guessing fuel struggles to climb up the slight incline into the float bowl when the bike is not running and there is no vacuum.

But still doesn't really explain why all the other DRZ owners around me have absolutely no issue starting normally.

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I actually only have a gravity feed tank, and never have issues starting it.....

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