idle problem/jetting question 03 EC250

[bryanaverill]

Any recommendations on improving idle stability? My idle gradually slows and the engine dies unless I adjust the idle speed quite high. I have played with several pilot jets from 35 to 42. The 42 seems to give me the best throttle response and low speed lugging power that I need for tight single track woods riding. The leaner jets cause a bog in throttle response. I have adjusted the idle jetting and air screw according to the traditional method of maximizing idle speed.

Current jetting
main: 175
pilot:42
air screw: 1-1/2
needle: CCK (1)
slide: #7

Plug: stock NGK8 (not sure rest of code)

Pipe: FMF Gnarly

 

[GMP]

No altitude/temp specs given. CCK (1) is lean for 0 - 1000' Couild you be trying to compensate for a rich straight dia with a low needle position? I always had good luck with D needles on the 250s, Cs being lean sometimes. If it were mine I'd verify the carb is in good shape and nozzle not worn out, then try a D needle with a larger straight dia. (DDL, DEL) and see what that does. For C series a CEL has the same dia.

 

[bryanaverill]

Altitude 500 - 3500' (mostly 1000'). Fuel 50:1.

I've tried N1EF (stock) and N3EW needles. With various pilot and main jets and clip position. They were all worse in different ways. I may have missed the magic combo but my current jetting is very good other than the idle issue.

What part of the tuning is responsible for throttle response and/or a bog? It seems most sensitive to the pilot jet and air screw.

 

[GMP]

I'm on my third 250. They all ran well with a DDK/DEK and #7 slide, but the JD Blue is the bomb. I'm @ 1000' as well. '03 is getting old so perhaps your nozzle is worn. Needles are cheap, try a leaner straight section, if it idles the problem will be narrowed down.

 

[Jakobi]

Altitude 500 - 3500' (mostly 1000'). Fuel 50:1.

I've tried N1EF (stock) and N3EW needles. With various pilot and main jets and clip position. They were all worse in different ways. I may have missed the magic combo but my current jetting is very good other than the idle issue.

What part of the tuning is responsible for throttle response and/or a bog? It seems most sensitive to the pilot jet and air screw.

Like GMP said. If your bike is truly happy everywhere but idle and you're not compensating for a rich idle by lifting the clip and winding the idle in, then use the name needle with a thicker straight diameter.

If moving the needle clip has any impact at all on the idle, then you have not set up your idle circuit properly.

Go a leaner diameter. Start middle clip. Back idle speed screw right out. Then in just enough to lift the slide. Try pilot jets with air screw fixed at 1.5 until you find the one that idles best. Then tune your needle clip position, then your main.

A change in diameter may require a change in pilot to maintain the idle mix. You can fine tune the AS either side of the 1.5 turns once you have the bike idling.

 

[bryanaverill]

My idle adjust screw (thottle stop) is almost all the way in and the idle is high. This obviously means my main circuit is providing fuel.

I'll back off the idle adjust screw until I get a medium-low idle (which it won't sustain because I've already tried). This should take the main circuit out of the equation, right? Then I can diagnose my pilot circuit by pulling the choke. If the engine speeds up then the pilot jet is lean. If the engine speed slows then the pilot is close to correct. If it dies suddenly then the pilot is too rich. All correct?

If I have success with this procedure, how do you fix a bog without adjusting the pilot jet? Needle diameter, taper, clip? Thia is my main question?

 

[stainlesscycle]

needle diameter will probably fix it. you will need to change pilot to compensate for the wider needle. don't know if you can modulate the choke enough manuallly to be able to see the changes

back your idle screw out to 2.5 turns out. get a leaner needle diameter, start with a larger pilot. maybe 48ish. go 1.5 out. start turning air screw out 1/2 turn at a time with 5 second pause between it until engine speeds up. if it doesn't speed up by 3 turns out you need to go leaner on the pilot.. and repeat air screw adjustment. you may need to blip the throttle in betwee air screw adjustments to get motor to settle down.

 

[gasser]

. If it were mine I'd verify the carb is in good shape and nozzle not worn out.

How do you check it Glenn? I can't tell by just holding it up to the light and looking through.

 

[bryanaverill]

OK, I read the other idle thread. From what I can tell the secret seems to be a lean needle straight diameter and a rich PJ (compared to stock). This is what you have been telling me all along.

I have an N3EW which has a 2.735 straight diameter. This is A LOT LEANER than the CCK that I'm currently running which has a 2.695 straight diameter.

I also have the problem with a hanging idle as descibed in the other thread. I guess this make sense. The engine is basically running at a high idle on the main circuit. Then the idle speed drops and the pilot circuit is too lean and the bike dies.

So I'll try the N3EW needle and a #45 PJ. I don't have a #48.

 

[stainlesscycle]

i plugged n3ew vs. cck into jetting chart.

cck(1)/42/175

is almost the same as
n3ew(2)/45/175

but there's a big rich spot 1/8-1/4 throttle. so that should get you close. you may not even need to go to 45 pilot - depends on how close to the edge your jetting is.....

 

[CACTUSREID]

i've had great luck with a leaner #8 or 9 slide in that series of bikes. you can chase your tail with needle changes for as long as you want,but as these carbs get a bit older and worn the leaner slide brings everything back into focus. my buddies and i get to ride huge amounts of hours compared to most guy's in a week/month/year,and we were one of the first to discover that the nozzle on the carb actually ovals out over time. once you lean out the slide,the other variables-pilot,needle,a/screw and main show much more response to changes. caveat- this free advice is worth exactly what you paid for it!

 

[bryanaverill]

Update.

I tried the N3EW(3) #45 PJ and it was too rich and would not idle except with the idle adjust screw turned all the way in. I swithed to a #42 PJ and it idles a little better but there was a severe bog in throttle response.

I switched back to the CCK(2) and a #38 needle. The idle was about the same but less bog. At least I could ride it.

I measured my needles with a micrometer: (CCK=2.695, N1EF=2.705, N3EW=2.735). The nozzle measures 2.89/2.90 with a gauge pin. No apparent wear on the nozzle. My reeds, ignition, power valve appear to be in good condition. The bike has excellent compression and starts easily.

At this point, the bike will simply not idle unless the adjustment screw is all the way in (spring solid). The air screw is not very sensitive. It seems to idle better with leaner PJ and/or air screw 3+ turns out. If I do either of these, it has such a bad bog that it's not ridable.

I seems like the main circuit is providing fuel at idle. It would take a needle much bigger than 2.735 to stop it.

I'm pretty much at the end of the needle experiment. What about a #8 slide? Does that significanly reduce the main fuel flow at idle?

 

[stainlesscycle]

before you said 42 pilot with cck, but you went back to 38 pilot? if it ran best with 38 pilot, 45 pilot and n3ew is way way rich.... was 42 a lean bog? where was airscrew?

with 38 pilot, cck, here's some n3ew comparison that may idle better. notice the dip at 0-1/8 throttle. that's basically what you need to idle. the one that's way rich is the 45/n3ew - also notice you may want to go 1 richer on main before you get it sorted.

i don't know how on the edge of lean you are with 38 pilot/cck so try at your own risk.... oh and try doing all airscrew adjustments with idle screw about 2.5 turns out from solid. i took a look and saw that the slide is halfway up the idle screw travel at about 2.5 turns. mine is idling at about 2 turns..airscrew will have no affect if idle screw is closer than about 1 turn from all the way in..

 

[bryanaverill]

1) 42/CCK was too rich at idle. Switched to 40 then 38 PJ. It was the leanest PJ I could use without a bad bog. #35 idles even better but the bog is horrible.
2) 45/N3EW was too rich at idle. Switched to 42 PJ and it had a horrible bog even though the idle was still too rich.
3) went with 38/CCK(2) because bog was acceptable and I could ride it with a crappy idle.
3) All combinations had air screw 1-1/2 turn out
4) Taking the air screw out to 3+ turns improved idle and made the bog worse in all cases.
5) Touching the choke always caused the engine to die instantly.
6) Turning off the fuel and letting it run out of gas caused the idle to race briefly then die.
7) All combinations made a lot of smoke at idle.
8) All combinations had the idle adjust screw all the way in. Slide opening gap very close to 1 mm.
9) Carb is off bike and undergoing a labratory grade cleaning. No sign of any problems so far.
10) All other bike systems appear to be funtionong properly.
11) I have never been able to get a "proper" idle with the adjustment screw at a normal position.
12) At this point I have no idea what to try next. Everything on your chart has been tried. No combo results in a good idle AND no bog.

 

[stainlesscycle]

good compression? new plug - br8es? does it start easy? 1 kick every time - 1 or 2 kicks with choke when cold?? float height is correct?

if it was me, an i was completely stuck - i would start really rich with the n3ew, #3, make it burble on the pilot and main. then at least you have a baseline (rich yes, but it's a reference that you know, and you know it should progressively get better.) then go 1 step down on the pilot till it cleans up. and air screw has an effect. bike has gotta be hot or your pilot stuff will be irrelevant... then move the needle till it works best to 1/2 throttle. all this i'm sure you already know, but sometimes resetting/restarting finds things you missed..
.

your other option is to jet for best performance with no idle, and buy a leaner slide. that might work.

 

[bryanaverill]

Three kicks with choke on when cold. One kick no choke when warm.

I'm starting to wonder if my choke is leaking fuel into the venturi when closed. That's what it acts like. Besides the idle problem it's always been rich through the entire range.

 

[Jakobi]

Three kicks with choke on when cold. One kick no choke when warm.

I'm starting to wonder if my choke is leaking fuel into the venturi when closed. That's what it acts like. Besides the idle problem it's always been rich through the entire range.

Mate.. Yours and mine! I always thought I had a freak bike that loved it lean. Bet you have the handle bar mounted choke aswell?

My other suspision is the squish band being too fat and holding unburnt fuel.

I have a plunger style choke on order which should be here soon along with a few other needles. N3CJ N3EW and N3EH. I'll hopefully get to try the carb with a new plunger and then move on to a complete top end rebuild with either a head/squish mod or the S3 head.