Jetting a Keihin PWK w/adjustable fuel-enricher knob?

[yo_marc]

Hey all,

I'm having a little difficulty jetting the slow speed circuit and getting a clean stable idle on my RM250.

From the factory, the '00 RM 250's carb (Keihin PWK) has an adjustable fuel-enricher knob, with a small needle jet attached to the plunger. I suspect my problem may lie with the knobs adjustment.

The knob does not seem to serve a purpose like a Keihin PJ's choke does, in adjusting the idle speed. Not that I am aware of at least.

The '99 RM250 Keihin PWK doesn't have this feature. For the 99, the knob is non adjustable, and there is no needle jet below the plunger.  Both parts are however interchangeable in carb bodies.  Both carb bodies also have a slide idle-adjust screw.

Is anyone familiar with that adjustable choke knob on my '00?  Can you tell me what it's purpose is or perhaps what you have done to tune it?  I can't seem to get a reaction out of it.

Thanks,
-marc

[ford832]

If it's actually an adjustment,it will typically click when you turn it.According the manual for my 99 RM125,it had an adjustable choke knob but when I turned it nothing happened.Upon inspection,I decided it wasn't adjustable.When I called Suzuki Canada just out of curiosity the guy said -"oops,typo.It's not adjustable"  
Try adjusting your airscrew instead.Out is leaner,in is richer and see if it improves.If you need to go more than about 2 1/2 out or less than 1/2 out,you need a different pilot.

[yo_marc]

Thanks for the reply and info!

That's interesting the '99 manual listed it, but it only appeared in '00.  The knob does have clicks or detents to it.. 6 to a turn, and able to go 9 turns outs from fully in.

I was able to take a quick look at it in the carb body tonight.  Up around 4 turns out, the plunger starts to rise revealing part of the orifice.  I cant tell what the needle section below is up to.

I spent a fair amount of time these last two weeks testing different sized pilots. I went through a handful - #38 through 45, checking to see what ran best.  45 was stock, and I settled on a 42.  

What is happening with the bike is when you blip the throttle, the rpm's either hang for some time at a fast idle (not lean, just fast), and then gradually settle down into a low stallable idle... or the idle drops right down to 'almost stall'.  The carb slide idle adjustment screw is too sensitive - there is no in-between those two modes of idle.  A hair adjustment on the carb slide idle adjust chooses on or the other.

That made me think my pilot is way out, but a 42 provided the best throttle response off the bottom. I think I am right around 1.25 or 1.75 out on the air screw.. (much tweaking too place there too)

My current theory is that I'm starting to bump the slide too high with the idle adjust screw trying to find a decent idle... but with the slide further down in the body, there is not enough air/fuel getting through and the idle is way low.  Looking up the carb body, is like a knife-edge where the slide meets the body, with my current idle screw settings.  I'm thinking that choke knob and the needle valve assembly is supposed to let some additional air through without engaging the fuel-enrich mode until it's truly engaged.  I am not sure  

I was hoping someone has been through this madness.  I've never had such a difficult time jetting a bike!

It's a little late in my very quiet neighborhood to get out and fire things up... but I hope to try turning the choke adjustment 4+ turns out, tomorrow.  Sounds silly, but I don't recall ever trying to go that far out.

[yo_marc]

Funny, I ran some searches through google for info.. came across older posts of mine trying to work through this back in '03. 

[ford832]

Try blowing some cleaner then compressed air through the port at the bottom of your choke to make sure the passage is clear.
After that,set your carb so it won't idle and do your jetting from there.A high idle will make it difficult at best to properly jet off the bottom.
By the sounds of it,your idle is way high and you have the wrong pilot.
I'd put the stock pilot back in then temporarily turn the idle screw so it will idle then turn your airscrew in or out to get your fastest idle(blipping the throttle in between then letting it settle down) once you find that postition,count how many turns in to lightly seated.This will tell you which direction to go with your pilot.
Also,make sure you have no air leaks around the reed block and that your cable/slide aren't bound slightly or hanging up in the carb.

[yo_marc]

Thanks - I had a chance to work on the bike a little last night.  I like the reed block suggestion.  I can say the reeds are a few years old, but have low hours on them.

I have two carbs here, one from a '99, one from a '00 - I've swapped carb bodies, and numerous parts, so I dont 'think' it's anything internal to the carb.

As for the pilot - I'm pretty confident the 42 is what is best.  Stock is a 45, and it's a little fat.

I confirmed the slide is very near the bottom of it's travel - the idle screw is just slightly lifting it.

The air screw doesn't have much of an effect on idle speed - I have to tune the air screw like I'm tuning a guitar; by listening to the exhaust note as it idles (and checking throttle response).  My range of adjustment is around 1-out to 2, maybe 2.5 out with the 42 pilot.  Outside those numbers, the idle suffers.

I did toy with the choke adjustment yesterday.  It does raise the idle speed a bit when I go about 5 out of 9 turns out on it.  Anything above 6, and it richens up the mixture too much and the motor will chug down after giving the throttle a snap.

I have it tuned fairly well right now - but it's a very fine balance between the air screw, choke, and idle-speed screw.  It does still take a moment for the idle speed to settle down, but it idles decent.  I'm just not confident all is as it should be.  It was very difficult to get things tuned.  I never had this problem with any other bike.

Thinking through it last night, I had to wonder if it's a timing thing with the factory ECU.  It's a definitive high to low idle change.  Has anyone ridden a snowmobile that does this?  You ride, come to a stop, and the motor is whirring at a high idle, at say, 2500 rpm.. after 20 seconds it settles down to a healthy 'ping ping', at like, 1200 -- that's similar to what I'm getting here, except my idle isn't as clean as I'd like.

Looking at another message board this morning, I saw someone mentioning that their '99 RM125 had an issue where he replaced some of the electrics to fix it - he mentioned the ECU, coil, and solenoid. I would assume he meant the powerjet. He mentioned the similar symptoms, high idle, and little response from the idle speed and air screw.  He said it ran fine otherwise.

Any chance my power-jet is misbehaving?  I would assume I can just unplug it, and if that's the fault, jet around it.  Since I have two, I've got some ideas to test one on a running bike.

Hope this isn't against the rules, but here's a thread elsewhere with some grievances similar to mine.

[yo_marc]

Just to follow up on my ramblings:

Been researching the power jet and these PWK-PWJ carbs.  I understand the solenoid for the PJ is open by default, and closed at certain RPM's. 

I hear pretty consistently that it's closed in the upper RPM's (some reports say 9600+)  and there are people saying its closed down low, 0-1500rpms.

I'm still thinking this stuff through.

I do have a service manual, but I moved recently and misplaced it. I don't recall it giving much usable info for this stuff.

[ford832]

If you want to be a little more exacting,hook up a tachometer to it and adjust your airscrew to get your highest idle.This will tell you exactly where you are and whether you need a different pilot or not.If so,change it,set it until it barely just idles and fine tune your airscrew again.After that,set your idle until it just idles for 15-30 sec then stalls and you'll be about as close as you can be.It's unlikely a powerjet issue as those effect the top end only.
For a few years starting at about yours,RM's were notoriously finicky when it came to jetting.It wouldn't be a bad idea to check in to a JD jet kit for it.

[TMKIWI]

If your carby has the plastic idle speed adjuster, they wear a flat on the point where it touches the slide.
Then when you try and adjust the idle speed 1/16th of a turn it goes from not idling to idling too fast.
That was the problem with my 01.
It didn't worry me I just set the mixture up properly by doing 2nd gear roll on's. The bike didn't idle but was crisp off the bottom.

Screw out your adjuster and check.
That may be your problem, not mixture.

[ford832]

I've never run across that but on the other hand I only had my RM for a year before I traded it on the EXC  Makes sense though.Especially where it would tend to wear it tapered then when you turned it would go way high then lower again.Interesting.I suppose if you didn't want to replace it you could always file it true  and be all good again-for a while at least.

[yo_marc]

I appreciate the pointers guys  

I dug out my service manual, and got some good info out of it. (surprise )  For reference and to clear up any info I have above - here's the goods, paraphrased:

The bypass starter:  (what I've been calling fuel enrich knob).  The bypass starter affects the air/fuel ratio in the throttle range from 0 to 3/8 throttle.  The mixture will become leaner as the knob is turned out, counter-clockwise from full closed.  Use a setting between fully closed and 2 turns out.  Caution:  If the bypass starter is opened excessively, engine troubles, poor throttle response, and abnormal detonation may be caused.  Limit the opening amount to less than 4 turns.

The power jet / solenoid:  The power jet supplies the necessary amount of fuel to the carburetor bore for the correcting the fuel/air ratio.   When the rpms are under 8000, the passage is open.  When the rpms are over 8000, the passage is closed.

I checked out the slide screw, and it was pretty healthy.

I'm still toying with the motor.  I'm currently running the old '99 non-adjustable choke, and tuning from there.  Figured I'd take one variable out of the mix. Not to mention it just starts the bike better when cold.  I may go back and mess around with the adjustable one if I need something to do

[ford832]

Interesting.Keep us updated 

[yo_marc]

Just to follow up on this thread - I've done a lot of tweaking and tuning over the last few weeks, and I've got the bike jetted very well.

I am running the '99 carb body, the '99 non-adjustable choke, 158 main, 3rd clip on a '00 N3WK needle, 42 pilot, air screw 1 turn out.

I'm VERY impressed with the way the bike is running. One thing I found along the way, and like you guys were saying - I can either tune the air screw to get the bike to idle well - or I can tune it to perform well on the trail.  The bike does not idle for more than about 10 seconds, but I'm shocked at how well the bike responds at all throttle openings at all RPMs. Plug looks great, MINIMAL spooge, only smokes on startup.  This is not my bike!!

The '00 adjustable choke was nothing but trouble for me.  It was much easier to tune without it.

Thanks guys, for talking through this stuff with me.