Needle Tuning

[IcutMetl]

I've had a couple threads on here pertaining to issues I've had tuning my carb., but I think I'm finally heading in the right direction.

My motor is '88, fresh 67.5mm Wiseco with midrange port, Rad valve, 38mm PJ, factory airbox with holes in lid & UNI, FMF fatty, running thin head gasket portion 195+psi, 50/50 of 92 and 110 octane, 40:1 Super Techniplate. Stock sprocket ratios.

I broke it in & started with CEG needle on middle clip, 175 main, and 60 pilot, airscrew 2 turns out.

After the first tank, I was starting to get into it more and it was running like dump. NO power off the bottom- tons of clutching needed. Started harder when warm. Sputtered like hell in 1/2-3/4 range.

I went up/down on mains but no real change. Went down to a 55 then a 52 pilot, to every notch on the CEG, then bought a DGH needle and tried every notch on that. I got it better, but not nearly right.

Yesterday I got back at it again after about a week. I went down to a 50 pilot, 1.5-1.75 turns out on airscrew, kept the 175 main, and the 4th clip down (2nd one up from bottom) on the DGH needle and it's the best its been yet. I also noticed that my carb boots weren't sealing perfectly-fixed that too.

Now it always starts 1st kick when warm and has improved off-idle response in the tight woods. Has a nice strong, controllable powerband hit right around 1/4 throttle. Midrange still sputters some in the 1/2+ range, but once in 4th-6th, it will pull to wot. It likes to be shifted around 1/2 throttle and pulls the best there- I think that's the port + pipe combo.

I tried the 50 pilot with every notch on both the CEG & DGH, and this is the combo that worked the best. What would you guys suggest I try next to get rid of the midrange sputter when rolling hard on the gas? Seems like it might be a needle issue?? I was almost to the point of saying f-it and buying a 38 air-stryker but just don't wanna spend the money.

Sorry for the long post but thanks for the help!!

[rustyATV]

I always like to refer back to this as a sanity check every time I think about the carb.
http://img.photobucket.com/albums/v11/hoppy/calchart.gif

http://img.photobucket.com/albums/v11/hoppy/pj_34_39_jn.gif

Actually, I put these together on a Word document and printed out a few copies to take with me, so I can keep sane when I decide to fiddle with the carb.

Also, here's Duncan's jetting procedure

http://duncanracing.com/techfaq/Tech_keihin-carburetion-jetting.phtml

Notice the procedure starts with the air screw, then moves on through the pilot jet, needle, and finally ends up on the main. The main you should monkey with last, as it only really affects the upper 1/4 of the throttle.

FYI: My setup for warmer weather here in Georgia (about 1500ft elevation, I think) is #42 pilot, CEJ needle on 3rd position, #162 main, just to give you an idea.

You may want to see if you can go lower on the pilot. Start here, don't pay attention to anything else yet. Ride the quad at just off idle for a few gears (not too much throttle, or you get into the needle's straight diameter, the last digit), pull in the clutch, shut the quad off until it coasts to a stop, then pull and check the plug. Tune to a light tan, checking that the engine doesn't die when you blip the throttle or gets stubborn to start warm, which would indicate a lean condition.

Midrange throttle (1/4 to 3/4) is going to be all needle. Don't worry about the Main jet at this point.

The first part of the needle that comes into play is the Straight Diameter (1/8 to 1/4 throttle), last digit, for you ##G or ##H. These are pretty close together so that's probably why you didn't notice any difference here. If your quad starts and idles nicely, but has problems when you blip the throttle, this is what controls that. Unfortunately, all you can do is buy a few needles to play with tuning in this range. Check the plug using the same method for the pilot. If the engine wants to cut out when you blip it, it's probably lean. If it sputters and/or smokes, it's probably rich)

The middle digit (#E# and #G# for you) is the L1 length, and you can adjust this with the clip position. According to the second chart above, and #E# is two clip positions lower (richer) than #G#. You said it was sputtering here? Check the plug (as above) to be sure, but sputtering is rich. With what you have, the most you could lean it out here would be with the DGH and the clip in the top position. The richest would be the CEG in the bottom position. So maybe check those extremes and see which way the engine is responding.

The first digit on the needle (i.e. D##, or C##) is the taper, and is the upper mid-range. The D is actually richer than the C, which is backwards from the next two letters (higher letter leaner). Like the straight diameter, the only way you're going to be able to play with this is with a few needles. If playing with the clip settings doesn't work, maybe it's this digit, and you should try a B##. Verify you're safe with checking the spark plug.

Jetting takes time, especially if you have to order needles, so take your time and relax. It took me a couple of months to get my previously-redneck-owned YZ250 to a rideable state in the low to mid range. It still needs work in the mid to upper ranges, but works great for what I do with it right now.

[HAYESTRX250R]

Great post mang. I picked up some serious needle knowledge.
Worthy of a sticky?

[LONG-ROD]

. you did not mention plug or gap. gap it no more then 20 i try to get 19 on a br9es I run my same needle at middle 45 piolet 175 main. but I have a 39 pwk.

[IcutMetl]

I haven't checked the plug gap yet; I have a set of feeler gages and I'll put in a new plug and gap it this weekend. I hear .018 to .023 is prime. I use a B8ES currently.

I think I'm going to pick up a 48 pilot, and a few needles to try. I've spent a crap-ton on getting this carb tuned in good. I was surprised I'm having better luck going down with pilots; before I had a 55 and there was no port work at all and it was only .020 over.

Thanks again for the help.

[rustyATV]

The first time you REALLY jet a carb, it's a real pain, but after you get it close or on, then you don't need to mess with it a whole lot afterwards, though it's always good to check when you make changes.

Plugs and gaps are going to vary as much as opinions. Honda calls for a BR7ES, BR8ES or BR9ES depending on the year, but I use a B8ES by someone's recommendation and I noticed it started a little easier for hare scrambles. Loren Duncan declared that I should ONLY use BR9EIX, but I'm not going to ($$$$!). Yamaha calls for a B8ES for the YZ250. For gaps, Yamaha wants 0.020 - 0.024 for the YZ, I've run 0.025, not sure what Honda says, but as long as it's not getting excessive, I don't think gaps are going to make a huge difference.

[Jason Hall]

If you are using a PJ oval slide carb with the Idle adjuster/choke knob??? The first thing I would check Is to see If the throttle slide Is Installed with the cut out towards the back of the carb. If the cut out Is facing forward, the low end performance will be Horrable.

I almost always end up with a 45-48 pilot In my 250R's with a PJ carb. This will keep your throttle response crisp down low. The needle will mostly be noticed when you first throttle In, like just as you start to accelerate from a staedy speed. If It feels dirty, or spuddery when you throttle In, then raise the clip to lean the needle. If you get a booowaaa / flat spot when you throttle In, lower the clip to richen the needle.