Help out w/Powerjet ?'s

[Hillclimb#42]

Hey Guys,
  I need some advice for our Frakenstein Bike. Its our version of a Hybrid. 86 KDX 200 with KDX, KX and CR parts that make up the patchwork. This question is about the carburetor that we have mounted up. The bike came with a Mikuni that didn't seem to run very strong. We tried a Kehin that was on a CR500. That carb would rev fast and way up in the range. The problem for me was, it would die quickly, if I let off the gas. We tried a wide variety of slow jets, but could not get it to idle and it had trouble with a low rpm bog. If it was allowed to idle down, then a quick blast of throttle it would hesitate before revving. Now, we have a newer Kehin that came from a 99 (I think ) kx250 with a powerjet. This carb idles, has no bogging, and holds the power on the top-end well.
  I want to know, if I can hook up the powerjet and get even better results. The KDX still has the lighting coil or whatever, can I just hook it up to the power jet, or how does it work? I don't have any other resource for these kinda questions, so thanks ahead of time for your brain power.
 

[DoldGuy]

#42,
The powerjet gets it's "Signal" from the CDI box to energize in the midrange & to cut out in the upper RPM for added overrev. With out a CDI controlling the signal of when to turn on & off I would not recommend hooking up the PJ.

[BDI]

Please do not throw rocks at me for asking this. You do know that on the CR500 carb that you had, in order to get it to idle right you have to pull up the choke and turn it left or right like a volume knob in order to set the idle. Once this is done correctlty the bike should idle and respond to throttle blips very well. If you don't know this you would proably never guess it. As for the power jet I'm thinking you would have to use the computer but the man you should ask about this is Don You should pm him to get his attention on this.

[Hillclimb#42]

Yeah, BDI, we were aware that the idle worked like that. It was always screwed all the way out to idle and that made the blip worse. Less idle = better blip. We were unsure how that adjustment was changing the idle. Does it do the same thing as other idle adjustments, or is it opening the choke valve? We tried a bunch to get it running right, but thought we may have a needle problem, since we could never get it lean enough on idle.
  There is a diode-deal on the frame of the 250's the power jet hooks up to, but is it a different voltage feed than a lighting coil? Is it hurting performance to run without the Powerjet hooked up on that carb? It runs pretty good, but not sure if I can get the PJ helpin or not.

[BDI]

I figured as much but I had to ask. You never know even the smartest of people can over look things some times. I wonder if it had the wrong slide cut away for your app. You should try one of the pwm carbs on it. They make very good power. you can get them from sudco big bored. Your K-5 would like one I can promis you that.

 P.S. thanks for not throwing rocks

[KXcam22]

Hillclimber,
  With a few electrical tests and some thinking, we could probably get that PJ to work.

1. On a PJ KX250, unplug the PJ and measure the voltage that goes to the PJ connector and when (at what RPM) the voltage turns on and off.  verify if its AC or DC.
2.  Measure the KDX200 lighting coil voltage (again AC and DC) and chart it at several RPMs up to wide open.

What I am thinking is that it may be possible to add some simple electronic circuity so that the KDX voltage will increase to the value that will turn the PJ on at close to the right RPM.  It won't be perfect but may work not bad.  It is my understanding that the PJ opens at WOT to richen the jetting for max HP.  From jennings theory extra rich at WOT gives max HP but then then the bike suffers as too rich below WOT - the PJ was invented specifically to get around this. This is backwards to what Doldguy has posted.  Am I backwards? Cam.

[The Flyin Hawaiian]

The powerjet coil on the PJ equipped KXs puts out around 25w. I run my lights off of it on my 03,04 KX250s.

[Hillclimb#42]

Well, I got some info from Don46, like suggested, and he pointed out that too big of a carb for the application, (like the Cr500 carb) will add top end, but will lose bottom. And thats what happened. He told me that the Kehin was a far better carb than the stock mikuni. The problem that we are missing is that the old lighting coil is analog and the newer Powervalve is a Digital signal. Thats why I ask people on here. Thanks Don.
 I see the test for the Powervalve in the clymer, but its unclear of the power difference. Sounds like the carb will work well without the Powervalve hooked up.
 The magneto from a newer 250 will run a light? Hmmm. Thats what I thought too KxCam22, "it just opens up at max rpm's", but the tests suggest that it gets a steady increase in voltage relative to the rise in rpm's. 12v-15v
  This is a spare carb from the caravan. The 250 originally using the Powerjet Carb upgraded to a Lectron. If I buy a new Carb, it would be a Sudco for the Kx500, but am just trying to work with what I have available so far.
Thanks for the replies,

[DoldGuy]

#42,
The powerjet circuit solenoid is in an open position at all times until it gets a signal from the CDI to close at about 8500 rpm (if memory serves me) to lean out the motor producing a hotter Exhaust Gas which in turn speeds up the reflection wave in the pipe allowing the short circuited charge time to be stuffed back in the cylinder before the piston closes the exhaust. If you notice the heighth of the dump tube of the PJ it is set at approx 1/2 slide height (midrange) and that is where most motors have the biggest load & needs the most fuel. If you are currently using a lectron (PJ installed?) start the motor & watch the PJ fuel line to see the fuel start moving at about 1/2 throttle as it uses the same principal. I would think (?) a tuned 200 would take a 38mm carb as I use a 39 on a 125 (& yes it has NO bottom, Great mid & top) that is used for drags, but maybe you guys need a much broader power spread. Another good thing about the PJ PWK is that you have an additional jetting capability with the PJ (has it's own jet) circuit eve with out it hooked up electronically. Hope  some of this helps out in using what you have.

[don46]

If you wanted to go to a bigger carb look for one off a 98-99 kx 125 they were good carbs and only 36mm should work pretty good on you kdx.  As Doldguy says you can use the big carb on the 125, in fact the 93, and 94  (I think) came with 38mm carbs, the things ripped. for your application and the bike I think a 38 is to big. For hillclimbing I think a good running kx 125 would kill the kdx 200, the 200 has tons of torque but is much slower getting to peak speed, is there a reason you chose the 200 over say a 125? is it a class specifically for the 200?

[Hillclimb#42]

  Yeah its a 200cc Class. It just worked out for us, so far. The bike has some cool history. It was my Teammate Paul's first Hillclimber, and he now is rippin up a Triple. He basically gave it to us to fix up. It took alot more than I thought, but we got it together and I was the only person who wanted to ride it. (I'm the lightest) Its my first stretched bike to race. It is a total Frakenstein. Every spare part from Honda's and Kawasaki's that we had, were thrown at it, and everyone got a hand in on working(and paying) on it. We chased the carb problems around with spare parts, too. The Cr500 carb that we tried first was from a Pro Hillclimb cr500 set-up to run alcohol. Its been in a box since the 90's. We of course, switched to standard jets, but think the needle may have been worked on to add to fuel flow. This other carb from a 250, was a spare from another buddies bike, who swapped it out for a Lectron. Its kind of a low budget, high labor project, I'll admit. The 250 and the 500 are less of an experiment by nature.
  thanks for the advice, Don. We are gonna keep our ears open for a 125 carb, 36mm. We noticed that the carb was closer to the cylinder, and am glad that you agree with what we thought that did to perfomance. I am used to lots of mid range, but some people build for top end, others for bottom. Its revving good, so far, but there's always more...

[DoldGuy]

#42,
I have a PWK 36mm willing to swap out for the 99 KX250 carb if interested.

Don,
The 93 KX125 (in my opinion) is the strongest motor for topend they have made and they came with a 36mm carb, as mentioned earlier, running a 39PWK on my 93 and it runs pretty strong. I don't think Kawi has ever put a 38 on a KX125 from the factory, but has used the 35mm for a couple of years ( maybe good for #42 & his KDX200?)

[Hillclimb#42]

Thanks for the offer, Doldguy. We are sticking with this one for now. We put in some new clutches and springs, geared up from 13-45 to 14-47, and plan on being in the hunt this weekend. The 200 is running well. It has been sounding just like a 250, but pulled like an old mule. We thought the clutches were slipping a little, since it was screaming sounding, but not an abrupt launch. If it was, it was hard to test, but we bought new clutches just in case. We discovered that the new springs were at least 1/4" longer. Now the clutch lever has the spring tension, it should have.

#42,
The powerjet circuit solenoid is in an open position at all times until it gets a signal from the CDI to close at about 8500 rpm (if memory serves me) to lean out the motor producing a hotter Exhaust Gas which in turn speeds up the reflection wave in the pipe allowing the short circuited charge time to be stuffed back in the cylinder before the piston closes the exhaust. If you notice the heighth of the dump tube of the PJ it is set at approx 1/2 slide height (midrange) and that is where most motors have the biggest load & needs the most fuel. If you are currently using a lectron (PJ installed?) start the motor & watch the PJ fuel line to see the fuel start moving at about 1/2 throttle as it uses the same principal. I would think (?) a tuned 200 would take a 38mm carb as I use a 39 on a 125 (& yes it has NO bottom, Great mid & top) that is used for drags, but maybe you guys need a much broader power spread. Another good thing about the PJ PWK is that you have an additional jetting capability with the PJ (has it's own jet) circuit eve with out it hooked up electronically. Hope  some of this helps out in using what you have.

 
doldguy, 
The PJ must be activated by the frame mounted diode/rectifier. The test is supposed to give voltage rising in relation to the rpm's when tested at the diode. What are you saying about the powerjet circuit? It still affects performance even though its not hooked up? What's it doin without being hooked up? The PJ concept still has me confused, not discounting your info.
  There is small amount of powervalve pre-load adjustment. Would it help anything to keep the powervalves closed a little longer to recover some of the lost bottom end? Thanks again for your input.

[Hillclimb#42]

Got a couple more ?'s. We got the Mikuni back out and was talking about testing the differences between the Kehin and the oem mikuni. After a closer look, we noticed that the Carb has been bored. It looks to be about 2mm bigger than it was originally. Then we also noticed the slide has been machined. The bottom angle has been changed to a steeper angle.
 We were advised that the fast 200's on the east Coast, all ran their Airboxes, so we wanted to try that. For those of you not familiar with the old KDX's, they mounted the Air box at a 90 degree angle to the carb. The air intake is right up under the seat. How would you guess that more air restriction would help make it faster? What does changing the slide angle do to performance? Boring the carb out will help top-end, right? With these mods, am I better off running this Mikuni?

[don46]

#42,
I have a PWK 36mm willing to swap out for the 99 KX250 carb if interested.

Don,
The 93 KX125 (in my opinion) is the strongest motor for topend they have made and they came with a 36mm carb, as mentioned earlier, running a 39PWK on my 93 and it runs pretty strong. I don't think Kawi has ever put a 38 on a KX125 from the factory, but has used the 35mm for a couple of years ( maybe good for #42 & his KDX200?)

Can't remember if it was the 93, 94, or 95 that came with a 38mm carb, but they did and also had a 6 petal reed cage, whatever year they were rockets, in fact I bought a 38 carb and the matching reed cage and used it on all the future 125's until they added a powerjet in 99, then I had them bored to 38's