Power jet questions...

[renes]

What is the deal with the power jet. I plugged and unplugged the wiring and I didn't notice any difference. This is my first bike with one (1999 YZ250) and the past owner has the main jet really lean. I'm wondering if it is because of the added fuel the power jet gives. Should I notice the power jet being plugged in? A local shop suggestioned I unplug the power jet for good.

Also I've had bikes with Keihin carbs and the air screw does not effect the idle speed so it seems difficult to tune the lower jetting. But with Mikuni carbs I've had, the air screw does change the idle. Has anyone else noticed this? My current bike has a Keihin carb and I'm try ot tune the pilot circuit. It is not going very well.

 

[kawaguy]

yea hi there, i also have a keihin carb and the air screw doesnt do crap, the idle will stay the same wether its turned right in or pulled right out.

im lost

 

[CaptainObvious]

My KX125 had a power jet. Its purpose it to act as (simulate) an accelerator pump. The PJ circuit on my KX was too rich, so I leaned it back. Throttle response did improve.

Regarding idle and the airscrew, the airscrew will not affect idle as much as it will affect throttle response. In fact, the air screw should NOT be used to adjust idle. You adjust the airscrew to perfect your throttle response on the pilot, and to a lesser degree, needle circuits.

 

[dirt bike dave]

I thought the powerjet actually leaned out the bike at high rpm??

Consult an owner's manual for details on how to check the powerjet solenoid. If it is like the Honda, you can remove the powerjet solenoid from the carb and test it by connecting it to a 12 volt source. If the solenoid does not switch, it is bad. You might have bad wiring, so the solenoid might not be working.

If the powerjet was disconnected or not working, the previous owner may have put in a leaner main to clean up the high rpm running.

 

[usgpru27]

Well I have an RS and TZ 125 roadrace bike and the power jet on these work much differant. The power jet is used to fight off detonation at higher RPM's. Our RR bikes rev to about 13500 rpm and make power from 9000 up. The PJ comes on at 10,500 and off at 12,200. This again is to fight off the detonation from unleaded fuels. If you unplug it you actually leave it on. The solenoid is held in the closed position when running out of the range. It also is open from 0-4000 rpm to aid starting. My TZ runs a mikuni TX carb that seems identical to the TMX on my CR125 only without the PJ. We normally do not change these from a tuning standpoint. It is more of a constant. Guys running 100+ octane unleaded run them big and leaded guys pull them down a bit. Certainly the RPM ranges would be differant on a dirtbike but would like to know if function is the same.