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.

Piston and rings are less than 10hrs and the bore is in good shape. The misfire was there before I changed the piston, at the time I thought it could be the cause.

For giggles, because we're running out of ideas and new piston etc bring better compression, can you try a better gas, AV gas if you can get it easily, just to rule out that or season differences perhaps.
Obviously try new plug to see if any improvement. Check cap resistance or swap out.

Does it get worse as hot? Stator don't last forever. They get a little weird but usually heat breaks them worse.

I Have just ordered a compression tester to confirm its ok but I'm pretty confident it is.
I have a new plug cap on there and I tried a hotter plug yesterday, that also made no difference.
I'm gunning 98 octane fuel, avgas is 100 I think so might be worth a try if I can get any.
I am now thinking the stator is the most likely cause.
I'd say it is getting worse, yesterday it wouldn't even wheelie in 1st, not because of lack of power but just won't rev through quick enough. It doesn't seem half as bad in the higher gears when under more load though. Strange.

Wishing you luck. That's tricksy. My stator started doing odd stuff. It would micro die like if you were blipping over whoops you'd miss the timing of them. Then it got worse.
But they die in different ways/symptoms.

Took me a while to figure out the above, and I thought I was fairly clued up. Runs like a champ since then.
Saying that I'd hate to steer you into buying the wrong parts.

Coil? They're cheap. https://www.ebay.com/itm/15583197638...EAAOSwljhlLQEH

Especially if the problem is when the bike is hot, it could be a coil.

In dyno testing I've found some coils are better than others , but only really relevant to racing when everything else is at edge of compression etc.


. And I've certainly replaced them fault finding. I've found a few multi cylinder 4 stroke coils of the 80s fail.

But I can't honestly think of a cdi type failing. Usually what drives them. By all means swap out if you have one to hand, but don't arrange a ride thinking you've fixed it. Bit like the optimistic replacing the radiator cap when you really know the head gasket is blown. :)

I have actually changed the coil, as it was way cheaper than the stator I started with it on that side of things.
To be honest it's no worse when hot. It's strange, it starts 1st or 2nd kick hot or cold, idles fine, makes good power on top but just runs crap everywhere else. Compression tester is due to arrive on Friday so I'll see what that brings..

Thanks again to everyone for the advice/suggestions, it's appreciated.

You haven't left it for a while between tests? Or swapped in a blocked pilot jet between tests?
Will often start just fine but run badly.

I don't think so. I have been right through the range of pilot jets all in the same day and there was no difference (to the specific misfire).I was pretty convinced it was a carb/jetting issue for a while, to the point I bought another carb, rebuilt it and went through all the jets again.

Sorry, he wouldn't say. It was his "secret"...

jeff

What 2T oil are you using in your gasoline? We have found some "lesser known" oils will cause the motorcycle to run poorly at low engine speeds. Motul at 50:1 always runs well for us.

Another issue we have had is with older filters breaking down and obstructing air flow and/or holding on to water after washing the motorcycle. Check your filter and maybe try starting with the filter off the motorcycle (do not ride it without the filter).

The final issue we have had is after washing or riding through water, electrical connections get contaminated with water. Check each connection, clean with a spray electrical contact cleaner, and use dielectric grease to properly reconnect. One rider in our group had an electric horn go bad and the bike would not start.

Good luck!

Think you mentioned the silencer can't remember. The thin perforated core can crack and obstruct flow.

I'm using ipone fully synthetic at 50-1, I have also tried elf. The airfilter is new and the airbox is clear.
I made use all the electrical connections around the coil were good when I changed that but I haven't checked everything else. I'm going to spend tomorrow afternoon messing with it so will go through the wiring then.

It had an fmf silencer on when I bought it but was still a bit loud for the forests around here after re packing it so I got an original item. I haven't had it in bits but the problem was there with the fmf. It's probably worth re packing the original anyway so I'll put that on the list for tomorrow.

Well, the compression tester arrived this morning. I have done three consecutive tests and it read 95psi each time. I wasn't sure if it was a faulty gauge so I tried it on my trials bike and that was 125psi.
I took the exhaust off to see the piston, it still looks new and there is no carbon build up below the rings.
I have just taken the head off and the inner O ring looks pretty suspect at the exhaust port side, I can't see that it's been letting gas past but it definitely looks in worse shape in that area.

Replace and retest would be quick while you are already there.

I'm not a big fan of guages but the comparison to the Trials bike is eyebrow raising.

Assuming you had throttle open and kicked till needle stopped moving.

Well, I changed the head 0 rings and the compression remained the same, so I have tried a different gauge and it reads 115psi whereas the trials bike now reads 140psi (which is what it should be).
I have pulled the barrel to have a better look and check the ring gap, the crosshatching is still visible in the bore although there are a couple of small wear marks but I don't think they are too bad. The ring gap is .35mm, but the bore is marked in the combustion area above where the top ring is at TDC. I'm thinking this is likely it!