Needle advice
 

Hello all, I have an 04 300 ec that is rich at the bottom half of the rev range. I'm running 38 pilot, 175 main, N3EG on the leanest clip and the air screw 2.5 out.
I don't really want to go down to a 35 pilot and as I'm on the leanest setting for the needle I thought that would be the best place to start.
I love the power delivery with the N3EG but just want to lose the 4 stroking when holding it at a set rpm and stuttering when you roll on.
Any advice is much appreciated.

With an 04 the needle jet may be a touch oval. A needle with bigger base diameter but same taper may compensate.

You can also try a larger cut-away (leaner) slide. I have used this with good results to clear up off-idle stumble/burble when the bike is otherwise idling well.

Longer (straight section) needle with the same diameter/taper may work as well. Try the N3CG.

I continue to be a "leaner slide" ambassador. The slide has a large effect on 0-1/4 throttle smoothness, and affects the burble when riding at steady throttle and the "pop-pop-pop" on deceleration. It takes a #9 slide for me to make my 300s run the way I want them to.

If you're a racer, or don't ride much in that lower throttle range, then you probably don't have a need for it. But so far, I can't "get there" any other way.

I recently rode a couple of TBI bikes and they don't run cleanly in that range, either. I can even hear it on videos that I watch of them. It takes a tune or re-map to get them to run like a clean-running two stroke can.

Your description of "4 stroking when holding it at a set rpm and stuttering when you roll on" is what I have found to go away with a cut slide. Unless it's really severe, my guess is that most people find what you are describing to be normal and expected.

Just IMO, I know there are other perspectives out there. But I don't think the leaner slides have gotten much attention, and I'm not sure why.

BTW in this case, F5 is likely right and you may have something else going on.

Jeff

If you are running a 38 pilot and looking for something leaner - then you are "pulling over" ... You shouldn't have your idle screw turned all the way in - if you do - then fuel is provided via needle versus pilot at low rpms... This is typically the case if you are running a 38 pilot and looking for a leaner pilot. What drives one in this direction is a bad needle along with bad idle screw setting... (as a start).

Start with getting a good needle - cut slide to #8 from #7 helps. Make sure you reset idle and air mixture screws when you switch over to the better needle - I would start with 42-45 pilot and 178 main - this may be different depending on fuel in your country... Aim for 2 to 2.5 turns out on air screw, and back out the idle screw (espcially if it is cranked all the way in to the point of being coil bound by the spring)- this will give you more fuel/air on bottom from pilot circuit in carb. This circuits in the carb need to be "better separated" - and this helps in this regard.

As was previously noted - the needle jet, the orifice that the needle slides into, becomes oval in shape with hours on the bike - it is not replaceable. Ron and RB-Designs was fixing these when he did his "carb mod" - which really addresses the pilot circuit sensitivity (or lack thereof) in the pwk38...

jeff

Thanks for the reply. The n3eg needle im using is pretty new , I wasn't sure at first if my carb it's self was worn so I bought a good condition secondhand one and changed the seals etc but it didn't change anything. The biggest affect I see is changing the clip position but I'm now on the leanest position so I have ordered a n3eh and n3ch. I really hadn't thought of changing the slide but that's a good call, I'm currently using a #7 so will maybe order a #8 depending on how the needles go.
As you say if i was at WOT everywhere it wouldn't be an issue but I spend a fair bit of time just bimbling through the woods and would like to get it spot on for my type of riding
Thanks again

Jeff, do you know what kind of modification Ron did to the pilot circuit? I have one of his carbs, and have always been curious about the "pilot sensitivity" part of his work (is it enlarging a passage or jet or ???).

Well, I'm at a loss now. I have tried the leaner needles and it was clearly running lean but I still had the same symptoms that made me believe it was rich. In the meantime I have swapped the carb, reeds and coil, none of which made any difference to the misfire. The power valve is operating properly and there are no signs of issues with the crank seals. What I have noticed is the plug always looks way too clean. This has been in for about 5hrs.

How is your compression? How many hours on your piston and rings?

This is where I would start if you can definitively rule out the carburetor and jetting.