Slide Theory, Carb Models, and Jetting

[Jakobi]

Looking for peoples settings and the slides they are running, along with the carb model. This is a bit of a continuation of GMPs findings in his 2012 model, along with some info from another forum where 2 x 36mm carbs have reported good results using the JD Blue and a 40 pilot. One has a 6.5 notched slide, unsure on the other.

My particular bike required the idle to be turned in all the way with the stock F diameter needle and a 40 pilot just to substain something that you could barely call an idle. After trying all combinations, a 40 pilot and W diameter gives the best idle, which doesn't hang, and only lightly burbles off load. Going richer to a H diameter needle I get more burble and only slightly more torque. This is all with a non notched #7 slide in an 38mm ASII carb.

You'd imagine the smaller 36mm ASII would prefer leaner jetting due to an increased air velocity, along with the richer slide, so it has me wondering, does the notch make that much difference??? or are their other variables at work.

 

[GMP]

Borrow a notched slide if available and run it with known jetting for a comparison. My point was that it seems to have more effect on my older carb than what you hear about on the new carbs. I'm pretty good now with my standard JD Blue jetting I've used for years. I will go back and try some of the Suzuki NED/NEC series though. Screw top carb is easy.

 

[twowheels]

Screw top carb is easy.

Show off

 

[swazi_matt]

Where is the notch, how can I tell if I have a notch or not?

 

[Jakobi]

Based on your bikes jetting preferences I'm going to guess yours has no notch. Just a guess though!

The number is stamped in the bottom, the notch is visible below that. Basically just a small window where the neelde runs past.

 

[swazi_matt]

Ok yep no notch on my no7

 

[Jakobi]

Ok yep no notch on my no7

And 38mm PWK ASII with the shallow bowl and flat top?

 

[n_green]

I have a 36mm carb with the notched 6.5 slide in my '11 300.

Using 42pilot, AS 1.5 turns out, 165 main, NEDW #2. Was quite snappy with this jetting, may have been ever so slightly on the crisp side on the pilot or straight section. Also hung on occasion coming back down to idle for a second or two. Pulled quite hard though and had a good top end.
Video:
http://youtu.be/Lv8RNTB9d5E


Using 40 pilot, AS 2.25t.o, 172 main, JD Blue #3. Has bucket loads of torque and an inability to stall that pulled with tractor like grunt through to the top end. Perfect idle, though was a bit low compared to previous jetting with idle screw left untouched. I think I could go one step leaner on the pilot and maybe even on the main as the top end wasn't as impressive as the NEDW jetting.
Video:
http://youtu.be/X2QAzqjk7F8?hd=1

In 2 weekends time I'm going for a weekend ride with a mate on a '11 KTM 300. It has a 36mm carb and is running a non notched #7 slide. I'll fine tune my current jetting to where I love it and then whack in his #7 and leave everything else and report back. I'll grab a comparative video and post up as well, might be able to hear the difference if any?

 

[GMP]

Yes that would be interesting. I'd like to try a #6.5 notched in my older carb but its not a standard slide and I'm not paying KTM big bucks for it. I suppose I could make one from a standard #6.

You go from a NEDW to a JD Blue with the same slide, wow, thats a huge jump in needle dia. If your bike runs the Blue good down low, try the NEDH/NECH, NEDG/NECG. Maybe that will balance the good top end with more grunt than the W dia that sounds lean from your description. The 300s have so much low end you can afford to drop some in a trade for linearity, as long as the bike is not too lean, but you have to be careful as the reason the torque falls off is the bike is slightly lean. The 250s go flat fast if you attempt this. I do not like the way they feel with super clean jetting, better a little fat down low with good grunt into the mid. JD Blue does this, with a hard pull through the mid.

 

[Jakobi]

Yes that would be interesting. I'd like to try a #6.5 notched in my older carb but its not a standard slide and I'm not paying KTM big bucks for it. I suppose I could make one from a standard #6.

You go from a NEDW to a JD Blue with the same slide, wow, thats a huge jump in needle dia. If your bike runs the Blue good down low, try the NEDH/NECH, NEDG/NECG. Maybe that will balance the good top end with more grunt than the W dia that sounds lean from your description. The 300s have so much low end you can afford to drop some in a trade for linearity, as long as the bike is not too lean, but you have to be careful as the reason the torque falls off is the bike is slightly lean. The 250s go flat fast if you attempt this. I do not like the way they feel with super clean jetting, better a little fat down low with good grunt into the mid. JD Blue does this, with a hard pull through the mid.

I noticed this when I did the 300 to 250 change. The smaller engine needs the fuel to make the torque where the 300 can get away with being a bit leaner. Also agree it sounds like the bike was a bit lean if hanging idle and such. Maybe due to clip position, maybe due to the diameter. I'm guessing a combo of both.

I'll be super interested to hear the outcome of the slide test and also to hear how anyone gets on running a richer diameter on the suzi needles.

 

[GMP]

I can tell you now that in mine with the notched slide the NECF was not too bad, and if I could get an NEDE/NECE it would have been even better on the bottom. I may just pop in the NECF with the non-notched slide and see where things fall, but screwing around time is running short and I'll race with what I know. With 250s you spend more time on the pipe so a clean low end is less critical as long as it pulls good out of it. Just shy of an obvious burble is where they like to be when you have to claw up the side of a mountain with no momentum, or pull out of a tight, deep sand berm.

 

[n_green]

Interesting info re notched slides from KTMTalk

Borrowed from a topic similar to this one over on the Pumpkin forums:

Now back to the notch. I don't fully understand it's purpose. I know what it does but I don't know why the need. I have slides with and without the notch. When you have the idle speed adjusted for an un-notched slide, swapping in a notch slide you will notice a slight speed increase. To get the idle speed back you'll need to tweak the idle speed screw lower just a tad. You will also need to adjust the a/s or swap the pj for a size leaner. I've tested both slides back to back and made the adjustments mentioned and I can't feel any difference in the engine.

The slot alters the flow and possibly the transition time when the pj by-pass outlet reverses and all pj fuel flow reverts to the pj outlet. The only purpose I can think of may be for slightly better launch immediately off idle, but again I can't feel any difference.

 

[rod]

For those of you wondering about the differences between slides, why doesn't someone just ask keihin (japan) themselves, at least it will be from the horses mouth if they reply.

 

[v-tec]

For those of you wondering about the differences between slides, why doesn't someone just ask keihin (japan) themselves, at least it will be from the horses mouth if they reply.

I cant speak japanees LOL

 

[Jakobi]

Haha good idea Rod. I think you should take the lead role on that one


I don't know if its just the slide. I kind of doubt its entirely the slide thats making so much difference and more likely another difference between the carbs. Today my pilot jet got clogged by some crud. Amazing how much difference such a little hole makes.

 

[GMP]

No, its not just the slide. Thats why when comparing and recommending jetting here you have to be aware of where people are what they actually have as far as displacement and carb type. Then you can factor in the expected tolerances that cause typical jetting variations.

I've read all the threads on the pumpkin forum and in theory it makes perfect sense, but this is relative to the newer carbs. What does not make sense is how my particular bike with the older carb acts with the notched slide. It is ABSOLUTELY leaner off the bottom with the notched slide, not richer.

Someone with a new carb please measure the distance between the back of the slide and the pilot hole in the spigot, I'd like to see if it is different than the older ASI carb. The new carbs are shorter overall, and jet leaner. If the dimmension I mentioned is different, it might explain something.

 

[Jakobi]

Hi Glenn,

Most definitely agreeing with what you have said so far without a doubt. Particularly while giving jetting info. Its a huge list of information you have to get before even thinking about making a suggestion.

Besides the slide and notch or non notch, I am finding it very strange that the 36mm carb appears to like richer jetting on the bottom end than the 38mm carb. It goes against logic.

 

[GMP]

Bike runs like an animal with the JD Blue jetting, non-notched slide and the head mod. Crazy fast on the top end, more than my previous 250s. Raced today on a fast course with some big straights and it has more than I need now. Fuel economy is great as well, used less than 2 gal in 2 hours. It spooges like crazy too.

 

[twowheels]

Besides the slide and notch or non notch, I am finding it very strange that the 36mm carb appears to like richer jetting on the bottom end than the 38mm carb. It goes against logic.

It's been theorized that the smaller bore presents a stronger vacuum due to the smaller area and draws more fuel, (somebody could calculate the differences in open area at different throttle openings) I suppose because the engine at a given rpm will pump a set amount of air so the air speed would be higher.

(thinking and typing, perhaps to my peril ...)

 

[Jakobi]

It's been theorized that the smaller bore presents a stronger vacuum due to the smaller area and draws more fuel, (somebody could calculate the differences in open area at different throttle openings) I suppose because the engine at a given rpm will pump a set amount of air so the air speed would be higher.

(thinking and typing, perhaps to my peril ...)

Affirmative! Logic dictates the higher velocity will draw more fuel for a given jet size, however people running the 36mm carb are finding better results using the JD Blue in the middle clip, 38 pilot, 6.5 notched slide, ASII. My 250 felt too rich with 38mm carb, 40 JD Red middle clip, 7 non notched slide, ASII. Obviously they are running about 170 mains where I'd be running a 180 as per normal theory. The rest has me scratching my head though.