Question on setting idle on Keihin PJ carb

[Blown 331]

I finally got my 85 250R jetted correctly and its running great all all speeds but there is still something not quite right. On a PJ the idle is set by turning the choke knob. To get it to run right I have the choke knob unscrewed all the way. And when its like this the choke knob has almost no up and down movement, so when starting I have to hold up on the choke while kicking because it doesnt move enought to click into the open position. I thought scewed out all the way was rich but when I screw it down some the bike cuts out and seems to smoke a lot so I'm not real sure on that. So which way is lean and which was is rich, and why do I need my choke knob screwed all the way out? Would changing the pilot jet affect that? I think I have a 55 in it. The bike has compression, ESR pipe and rad valve. 185 main jet, 110 octane, no air box lid. It idles and runs great at all speeds but I'd like to have normal choke operation. Thanks.

[barnett468]

Hello;

The links below might help until someone can explain it for you. You might need to change your pilot jet to get it is range. If it does not have a flat spot/hesitation right off idle the pilot may be fine.

http://www.carbparts.com/keihin/need..._your_carb.htm

http://www.keihincarbs.com/tips/gate.html

[Blown 331]

There is no flat spot or hesitation. It appears those links are for a PWK which does not have the idle adjustment on the choke knob, I have a PJ.

[shortline10]

In my experience its usually a throttle cable issue or small jet issue .
is this a new carb ? is their a little slack in the throttle cable so the slide bottoms out ?
Might be a simple as going up 1 size on the small jet and if its a used carb make sure the small jet is very clean .
If all else is ok lower the needle clip 1 notch so it raises the needle and see if that makes a difference .

[Blown 331]

Used carb. Its probably been on the bike for 10 years and I could never get it to run right at WOT, so just only rode up to about 3/4 throttle or so. lol. Turns out I was always way small on the main jet. Runs great at WOT with a 185 which is much larger than I see other people runnning so I never tried going that big but thats what it takes.
There is slack in the cable. I haven't checked the jet for being clean lately but its always been like this even when I knew for a fact it was clean so I don't think thats it.
Everything you are suggesting is richening the bike. So does that mean having the choke screwed all the way out richens it? So basically I'm maxed out on that adjustment to the rich side. I'll check the needle first, I can't remember where that is at all. Probably 5 years since I've been in there. If nothing else I can always just live with it since it does run great. Just sucks I have to manually hold the choke up to start it like this and it has almost no movement. Thanks.

[El Camexican]

I think (repeat THINK) that you might need to go down one or two sizes on your slow jet in order to get your idle/choke thingamajig (for want of a better term) in the nominal range. That gizmo is enough to drive a man to drink. I gave up on mine and when to a PWK on my Tri-Z, but now that I have my fuel pump issues sorted out I may put the PJ back on and try and to master it.

Good luck and let us know how it works out!

[Blown 331]

Yeah they can be a pain for sure. I've got a PWK on my 01 Banshee. My 90 Banshee has a PJ and its great all around. Both bikes have a single carb. I've also got another PJ, I thought about trying it on my Tecate.

[poohbee1]

I think I would pressure test that motor. 185 main wow that's big

[Blown 331]

That's exactly why I had incorrect jetting for 10 years. lol. This is the first 2 stroke I've jetted so I had problems determining if I was lean or rich at WOT. From what I read, lean would bog and I definitely did not have a bog. It also seemed to be the general consensus that 175 was about as big as a 250R would need so I never tried to go any bigger. I threw in a 175 and it would still cut out at WOT. No bog and I thought 175 would be rich. So I worked my way down and just could not get it. I did not want to do a plug chop for fear of melting it down if I was lean.
And heres how I figured it out. I picked up a built 01 Banshee with a single PWK, it had a 168 main and ran just like my 250R, perhaps worse, it made the most power at about 75% throttle, over that it would loose power. I did some research on that as well an it as general consensus that I was real close on jetting. Then I picked up a 90 Banshee with a single PJ. It was stock other than that, even has stock pipes. This thing was jetted spot on, whoever jetted it knew what they were doing, it runs PERFECT! It had a 180 jet. That was my first clue that the 01 was way lean. I threw in a 185 and it was better. Then I went with a 200, better yet and I had no bigger. I have a 210 on the way and I may even need a 220. As far as I know 230 is as big as they go. That was my clue that my 250R was just crazy lean even though there was no bog. I pulled the 165 and threw in the 185 and it ran perfect. And the power is unreal. By far the fastest untouched stock cylinder I have ever ridden. I'm almost wondering if there isn't some port work I don't know about. Its amazing. Super crisp.
And since all this I did more searching and found other Banshees running up to 230 main and other 250Rs running 200-220 mains (even on this site), so while it seems to be rare, its not just me. I don't run air box lids either, no one seems to mention that and it makes a big difference.

[El Camexican]

Did you check your float height before you started changing jets? If it's off nothing will work right.

[DohcBikes]

This could be a stupid suggestion but no one has talked about fuel mix ratio... could that make a difference? And is 110 octane suggested for a stock 250r... I truly don't know but just throwing that out there.

[barnett468]

Hello Blown 331;

Actually, the links I posted for you are in fact, at least part of Keihins official instructions for tuning a PJ carb as well as others.

I will post detailed directions hopefully within the hour, sorry but I just didn't have time yesterday.

Upm,

[barnett468]

Yeah they can be a pain for sure.

LOL.


The following is not from Keihin or the internet. If any of it is incorrect I apologize and encourage corrections. It is also incomplete.

I thought it might help people to "properly" adjust the following section of these lovely PJ series carbs if they understood a little about how the idle speed adjustment/choke knob worked on them. Just skip down to the adjustment section if this doesn't interest you.

The PJ carb is obviously a weird bird. Imo, Keihin tried t do what is nearly impossible, which is to make a carb that would idle properly on all motorcycles it was properly sized for without having an adjustment for the slide. Obviously it didn’t work out completely according to plan.

Many people either give up trying to set the idle or simply live with either no idle or no choke, or use throttle cable tension to increase the slide height so their bike will idle.

The idle speed adjustment/choke pull knob combo, is nothing more than a fuel enrichment circuit.



The way this set up works in principal, is a bit similar to the Keihins on the ATC 250 ES Honda ATC. The main exceptions are, the PJ carb has an adjustable idle air screw and the Keihin on the Honda has a fixed size air jet. The air screw is able to adjust air to the idle circuit from an amount of 0 up to the size of the orifice it controls. The idle speed adjustment knob and choke pull knob on the PJ, performs the same function [works the same way] as the idle fuel screw on the Honda Keihin.

This combo knob has two sections. One section is a needle which is raised or lowered by turning the idle “speed adjustment” knob either in or out. The position [height] of this needle partially controls the amount of fuel supplied to the engine on the idle circuit. The idle circuit provides fuel to the engine during starting also.

The other section is a plunger that when pulled, adds additional fuel to the bike for starting purposes only.



There are a few different ways to explain and approach the idle "speed"/choke adjustment of this lovely design, the following is just one. Some of these items were mentioned above by others.

IDLE "SPEED"/CHOKE ADJUSTMENT

1. Check float level, if it is too low it can cause a lean idle condition, if it is too high, it can cause a rich condition. Set it to the lower end of the recommended height then check idle again before making further adjustments.

2. Make sure there is a little free play in the throttle cable.

3. Turn the air screw all the way in until it just barely stops and count the amount of turns. The average might be 1, the max might be 3. If it is less than 1/2, and your idle screw knob is at the max limit, your pilot jet is too small. I would install 1 size larger.

4. Warm engine to operating temp then turn the idle "speed" adjustment knob [located on the choke pull knob] until the highest idle is reached.

5. If your idle air screw is more than 1/2 turns out, turn it in until highest idle is achieved but do not adjust it to less than 1/2 turns from fully closed.

6. Turn the idle "speed" adjustment knob until the desired idle speed is reached.

7. If your idle air screw is still more than 1/2 turns out, turn it in until highest idle is achieved again, but do not adjust it to less than 1/2 turns from fully closed.

8. Turn the idle "speed" adjustment knob until the desired idle speed is reached again.

9. Turn bike off and pull choke lever to see if it properly engages. If it does, you are done with this part, if it does not, install a 1 size larger pilot jet. This should hopefully create a high idle and/or rich condition at idle, in which case, you simply turn the idle "speed"adjustment knob in until the desired idle is reached.

If you turn the idle "speed" adjustment knob all the way in and the idle is still too high, simply turn the idle air screw out until the desire idle speed is reached.

If you reach a point where the air screw suddenly has little to no effect on the idle speed, you have reached the maximum range of its effectiveness. Count how many turns out it is from full in and make a note for your records. This point might be around 3 turns out from full in.

If you reach this point and your idle is still too high then the easiest way I know to achieve your desired idle speed is to reinstall the previous pilot jet, raise the slide a hair by putting tension on it by adjusting the throttle cable [this is not recommended because it can possibly create a potentially dangerous situation], return your air screw to its original setting and turn your idle “speed” adjustment knob in until the desired idle speed is reached.

You will need to fiddle with balancing all these things until the idle “speed” adjustment knob is in far enough that it allows the choke to properly function.



Ok, now if you eventually become one of the lucky few that are able to achieve idle nirvana with a PJ carb, but you now have a slight rich burble/hesitation just off idle, lower your needle 1 position at a time by raising the clip on it and PRAY that it goes away and does not affect your idle.



Ok, was that confusing enough?

[barnett468]

Hi Blown 331;

Is your screen name a reference to a stroked small block Ford?

If so, is it the one used in your Avatar photo that appears to have a problem keeping the wheels on the ground?

If so, does it happen to run under 10.5 in the 1/4?

[Mosh]

I would be cautious on taking jetting advice while not listing more specifics. For instance what size is the carb? 34-36 mil?
Any porting done to the engine?

Now assuming it is a stock 34 pj and no porting and a 250 based cylinder you would be way to rich on the pilot. Where is theair mix screw set? I would guess you have that screw backed out at least 3 turns just to get it to run.
The choke circuit on those carbs are confusing. You think they are adding fuel when you screw it out. But you are actually adding air when that knob is pulled up or or screwed out. If that bike does not rev hi when its cold and choked the pilot is to rich.
Either way if the engine is fairly stock other than the pipe and reeds and the carb isa factory 34 with 55 pilot and 185 main I would be working down on jets. Probably around a 42-48 pilot then re check the main.