Dyno Chart Listing
 

For those that are looking to unlock HP and TRQ . Latest chart on top. Obviously I am still too lean for max power with the DG-R + Stock Header. I am still too lean in the upper RPM range with the full FMF system for max power..

EDIT: 4/10/15 - It looks like the below chart is not valid. The operator is sure that run was in 3rd gear instead of 4th.. I'm going back in hopes of getting the correct chart off the dyno...

Edit 6/16 - This is an old and outdated thread. Proper lidless fueling with slipon, near sea level, is with kit DJ2152, DJ140/K152 main jet, needle clip on 2nd notch down from the top(2N). With full exhaust, DJ144/K158 , needle clip on top notch(1N)..
See the proper thread below on my signature line..

Attachment 9041







Attachment 9042







Attachment 9043

That's a sizeable increase in torque, it actually looks like a curve now. The AFR did change but not much from 5k to 7k rpm. How does it ride now?

Tell me exactly what you are comparing/analyzing - The DGR curves ?

I wonder what's causing the FMF system to go rich under 5k compared to the DG system? I am wondering if you would make up some of the difference if they had comparable a/f. 2 lb/ft is a sizable difference.

Yes the FMF consistantly causes a very different AFR chart than the DGR + stock header..
The AFR with the FMF only gets lean toward the upper end - which is not good ... The 12:1 in the midrange is about perfect for power production, that's the 5N doing that..

There is more HP and TRQ available with the DGR if only I could get the AFR down close to 12:1 throughout the range - Probably a lot more HP/TRQ can be found ..

If I'm reading that first chart correctly, re the Tq, I'm seeing that the Megabomb/PC4 combination might have a little more Tq at the top end, but losing a considerable amount compared to the DGR near the bottom end. I'd gladly lose a little torque at the top end to gain what appears to be almost 2LbFt of torque down at the 4500RPM range. I wonder what the PC4, without the Megabomb (using the stock header) would produce for Torque - close to the stock header/DGR combination?

I do find it funny that they use the wrong label for torque measurement (Ft Lbs instead of Lb Ft.) on the charts? (http://en.wikipedia.org/wiki/Pound-foot_(torque))

Loss of 2lb ft and about that much in HP as well...

I am going to have to go ahead and Dyno the PC4 + stock header... I can't get it out of my head that I don't have data for what could be the best combo for HP and TRQ.. The DGR maintains stock header I.D. all the way to the muffler, that's for TRQ... The PC4 has a larger ID - so from the end of the header to the muffler is a bigger pipe - And I don't know how that will affect overall power production... I guess I'll dyno it..

Just test rode with the PC4 + stock header..This is the first time I've done this config as it did require damaging the stock header gasket/seal in order to remove it.. The PC4 will not slip into the stock header until you remove this seal.. I've been riding today with the DGR and wanted to compare while the DGR power is still fresh in my mind..

Low end response and power are less than DGR - as expected.. MIdrange power hits hard starting at about 5k - we are talking wheel spin starting at about 5k on hard pack clay "dirt road"... Top end power is a question mark - I couldn't make a determination - It should be better than DGR..

I suppose I had better do another Dyno run on this config..

Went for a long ride today with DGR.. Big power in your face with every blip of the throttle.. Offroad, on the trails, we are talking wheel spin with every blip.. It'll wheelie on power alone while spinning its' rear tire.. No, its' not like my FE650E or KX500 but it is exciting nonetheless..

The torque curve for both now looks like an actual curve.

Looking at the DGR AFR curve, it seems the extra turn on the screw richen up a bit below 5,750 rpms. Guess you do need a large pilot as you stated if you want to get it richer.


Also, it looks like the 5N richens up at the same point around 5,750 rpm as the 4N. From there it is richer with 5N until 6,500 rpm than the 4N, then the 5N leans out to match the 4N until around 7,500 rpm, that is strange to me.

The other strange thing I see in the DGR AFR curve is that the 5N is leaner from 7,500 rpm and up than the 4N with the same main jet, this is what you described in your first tests before the dyno. Could it be you are right and the bowl doesn't have enough capacity to feed the 5N and 136 main?

Thanks for sharing this, your dyno charts are definitely the best jetting comparison for the KLX250 that I have seen.

KLXSTER,
You could reduce the size of the main jet air jet. That will richen up the high RPM range. The .5 mm air hole is correct for the stock air box, lid and snorkel. It works for me.
Attachment 6981

Well, the second chart is 136/3N.. The only chart using 4N is the third one, and that is with the 132..

But yes, there are questions that need answers between the DGR AFR's on chart 1 and chart 2.. I watched and participated in all dyno sessions. I know the operator operates the throttle in a consistent manner. Therefore, the variances should be due to adding 5N and 3.5 out( 3.5 turns out on the fuel screw) to the #136 main jet..

Since this run, I have reset the float level from 15mm to 14mm.. I am going to try to get a Dyno run today with the stock header + PC4 ..

One point - I am convinced the FMF continues to make bigger HP well past its' chart cutoff point of about 8400 rpm. This is from ride tests where it just pulls like hell all the way to ignition cutoff (10.5K)..

I haven't dyno'd a bike (or car) before - but why do the charts basically start at 4500 RPM and cut off at 8500/8700 RPM? I'd be interested to see from down low, all the way to redline - is it just the dyno operator's preference?

IceBikeDave, I am unfamiliar with the mod you describe and don't understand the underlying theory behind it.. If you have data on before and after and details on the mod, I'd be more than happy to try it.

I thought I was the only one here that believed that, glad to see I'm not. At least in gear 1-3 I can hit the rev limiter without even thinking about it and there is power there. I can be cruising at 8 or 9k rpm and open the throttle and get to the rev limiter almost instantly, again, in gears 1-3. It's very useful for riding in heavy traffic as I do daily and shifting would be slower in cases where you just need a quick pull to get ahead of someone. I don't have the full FMF as you do so you probably much better top end with the full system than I do.

rgmr250, the dyno operator controls the rpm range that is charted.. I have asked him to start at 3.5-4k and go to 9.5k.. But that is not what happens.. He pushes a handheld trigger button to start and stop the charting while the engine is rev'ing.. I was sure he was hitting it at 4k and going to 9.5k... So I don't know..

IceBikeDave, Spent an hour online researching the Main Air Jet.. Looks like the FMF system could need a reduction in my main air jet orifice size to "fine tune" the upper end. Problem is, I cannot find data to help me determine what size I should mod to.. For instance, making the orifice smaller will richen the upper end - but how much smaller ? I need a formula or ratio for AFR change % per Main Air Jet change % ...etc etc

Go too far with restricting the Main Air Jet and atomization is lost - or suffers - and performance is lost. Apparently..

Klxster,

Sorry for the delay. I had my left hand thumb-base joint rebuilt yesterday. I am typing one finger with my left hand.

So, how dose the main jet air jet affect the fuel flow?

First some facts:
The area above the fuel in the float bowl is at atmospheric pressure. Practically always.
The vacuum at the top of the “needle jet holder” (emulsion tube, thing you screw the main jet into, or whatever it is referred to) varies. Not much at idle and much more at full throttle at high RPM’s.
The air jet supplies air to the chamber that is just outside that emulsion tube.
As the vacuum above the “NJ holder” increases the liquid in the nj tube rises and is sucked into the engine.
There are a series of holes in that nj holder. When the suction becomes high enough air will be sucked through the top holes and when there is more vacuum, then, the lower holes will bleed air. So, the main jet dose not have gas being “pulled” through it until just below max power output . The liquid gas just wells up into the mj holder cavity until just below max power output.

If the mj air jet was removed, and just a big hole supplied air to the chamber that is just outside that emulsion tube, the mj would likely never see any suction. Alternately, if you plugged the air jet with a small tapered rubber stopper, the mj would see suction at or near the beginning of the slide starting to lift. You can try this rubber stopper experiment.

The correctly sized air jet will prevent an overly rich mixture as the engine speeds up under a load. Or provide it if you wish.

The stock snorkel creates a good amount of vacuum in the air box at high RPM’s, we hate that. With the lid removed, less vacuum and more air to the engine, we like that.

That stock air jet works great with the stock snork. Open box top, lean running, not so much at 1500 rpm, really bad at 7500.
You can adjust that high rpm lean condition with the air jet. And probably in combination with the MJ also.

How to install different main air jets:

What we will do: Install a threaded bushing in the Air Jet cavity to accept threaded Jets from Jets r us.
We will be drilling and bonding in the completely disassembled carb body.

What we need:
(1) Locktite 680 retaining compound. 1 small drop (McMaster Carr)
(2) M3.5 x .6 tap (McMaster Carr)
(3) Forster #16 screw driver (McMaster or forsterproducts.com)
Screwdriver not needed BUT it is a fine tool.
(4) Jets: Description: GENUINE Keihin main jet size 40 – 45 - 50 (SKU- 1001-108 ) Jetsrus.com . The 50 is for going back to stock.
(5) Some Sintered bronze bushings. QBCbearings.com BSNPLNMP030506 PLAIN SLEEVE BEARINGS Each $1.43
I bought 7 so I could evaluate bonding strength.

Procedure:
Make sure the bushings slide into the existing jet cavity, On mine the bushing to housing fit was just a little less than a light press fit. The bushing slid in with finger pressure and the final positioning with a small screwdriver.

Disassemble and clean the carb. Q tip and carb cleaner for the air jet cavity

De oil the bronze bushings so the locktite will bond to it.
De oiling procedure. Soak the bushings in carb cleaner for an hour or so.
Place them on a white tissue to dry and bleed oil into the paper. Or ultra sonic clean it (them). Dry completely.

Drill the original jet. Drill the existing jet to.125”. I placed the carb body on the drill press table spigot end down. Just go through the brass. (don’t drill through the camber into the pilot circuit)

Bond the bushing into the carb. Spread a small amount of locktite in the carb air jet cavity, use a small wire and smear it around, try to get it halfway down the hole. Don’t glop it in, this stuff gets hard and will cause problems if it gets into a small passage way. Apply a small amount to the bushing side. Slide the bushing in so the exposed part of the bushing is about 1/8 “ pact the curved portion of the inlet bell. Set the carb on the diaphragm flange face and let it bond. I left mine overnight to cure.



Tap the bushing. In the same drill press I chucked up the tap oiled it well, disconnected the drive belt, had the wife hold the carb, I used one hand to turn the pulley and the other to move the tap down. Tap about 6 to 8 turns total. It takes very little effort. The tap drill size for a M3.5 x .6 tap is 3.1mm, the bushing id is about 3mm, I tapped the 3mm hole. Sintered bronze taps like butter.

That’s it. Put the 50 jet in just to prove to yourself that you didn’t screw things up. If I was trying this on a no lid situation I would next try the 40 jet.
Your main jet might need to be smaller now.

Somewhat related. Why do some(most) 2 strokes not use air bleed in the mj circuit.

Outstanding !! With this mod - if someone will "dial it in" for us - You could expand the power producing capability of the DJ kit ... For instance , 132/5N/FS3.5 and .4mm main air jet , could produce better AFR's and more power than I have now with 136/5n/FS3.5 and .5mm main air jet..(near sea level and lid off of course)

Your description of the processes involved are easy to understand and jive completely with what I found during research.. As I understand it, the emulsion of the fuel as it travels up the "well" is important for providing good atomization once it gets to the top of the "well" and hits the air stream... The main jet provides the metering of the raw fuel into the emulsion tube - the main air jet provides the metering of the air into the emulsion tube... A balance occurs or is created between the MJ and MAJ - the result of that balance is what your spark plug has to ignite at all engine speeds where the needle is unseated..

Ok.. thinking out loud again.. In order to get the bike to run with that snorkel ( and lid? )
you have to have a "biggy" MAJ in order to produce the desired pressure gradient for the desired emulsion in all situations where the needle is unseated. This delicate balance between the MJ and MAJ goes all to hell when you pull the lid. Lidless, you now have a huge MAJ providing huge amounts of air to the emulsion - causing leanness ... And this leanness (imbalance really) cannot be cured by simply throwing in larger main jets and raising needle heights - as I have done .... The desired AFR must be achieved by establishing a "new" balance between MJ and MAJ ...
Now, about the latest chart with 136/5N:
This explains why the AFR's stay lean with the DGR... The increased signal to the carb causes an exacerbation of the totally discombobulated MJ/MAJ tap dance.. This also explains the lean upper end with the FMF system - at those RPMs the signal, once again, to the carb is strongest and too much air flows into the emulsion tube through that damned biggy MAJ... 5N is the key, it fully exposes the flawed MJ/MAJ balance.

So, if I have this understood correctly, It's time to roll up our sleeves.. I bet 132/5N with proper MAJ re-sizing will scream, AND , 136/5N with a well re-sized MAJ will Scream+... (near sea level with lid off and a good slip-on...)

Klxster,
About that frothy fuel. I think the mj/maj “balance” as you named it, is the purpose of those jets. The frothy fuel is but a side affect of the process. I like that side affect.

Now, that emulsion tube thing. I switched the stock tube for a 13091-1985. Same number of holes but the top 3 rows are drilled about one row “higher” than stock. The mixture seems a little richer right off idle, everywhere else I cant tell the difference between the two. I think the frothing starts sooner and that froth is easier to suck out into the air stream. Also, it would possible to produce an overly lean off idle condition if the float height was set too low, thus exposing the top row of holes to the air above the fuel level in the air chamber which surrounds the emulsion tube. I think mikuni or dellorto call that tube the “Emulsion tube”.

I will solder two of the top holes closed and drill two new holes below the 3rd row when the cast comes off my right hand.

Problem I have is that the HP/TRQ I have now is so new that I'm not sure I can sense another HP (or maybe even 2) up high with the FMF system in place.

Looks like I have to gear up for a whole nuther series of experiments to gauge the effects of MAJ tweaking...

With the DGR on, I could start tweaking the MAJ as is - that setup could use more fuel everywhere - and should produce dramatic enough TRQ increases for my to seat-o-pants dyno to sense..

Great little mod Dave; very perceptive. https://s.yimg.com/lq/i/mesg/emoticons7/113.gif

I don't recall my CVK's a/f needing correcting with an air jet tweak, and I'm not running it anymore on my 250 anyway. Tuning with maj size applies to the pumper carbs as well though.

IIRC my TM36 as supplied from the vendor with no air jet in it, tended to go rich-er as the rpms climbed. Fixing that would require redoing the mj and maybe more if I added a maj. It's ok for now

:D

Ok, did a MAJ mod on my bike and went for test ride with the DGR.. Results are inconclusive because it's so damned powerful that I don't think I can tell another HP or two or another Lb Ft of TRQ or two. The AFR must be richer at Needle RPMs as well as transitions on either end of Needle RPMs.. I'm sure the bike runs stronger - it's just too new a power band for me to give a definitive assessment... It spins the rear tire way too much off road for me to get a good reading..On pavement - It hits the 10.5K ignition cutoff seemingly instantly with a snap to WOT at anything above 6K.. WOT in first, shift to second and instantly snap back to WOT will lift the front tire if I'm not sitting all the way forward. It's crazy fun..
Details: The stock MAJ is .1" . I rigged my old stock main jet (Which I have no need for..) as a MAJ with a .05" orifice.. My research indicates the CV requires a 1psi difference between the ambient air pressure that is above the fuel in the bowl, and the air pressure that has flowed past the MAJ and is entering the emulsion tube. The snorkel practically creates this differential in the airbox - thus the MAJ is a whopping .1" ... I have no idea what will restore the proper balance of MAJ air and MJ fuel in the emulsion tube running with lid off, but I guessed cutting the MAJ size in half would be a place to start.

Since this mod is a little involved, I guess it'll have to prove its' worth on the dyno.. From, what I've read, go too small with the MAJ and fuel atomization will suffer and performance will not improve..

Boatdriver has completed an initial ride using 136/5n. He reports fantastic results. This is a game changer because he is running standard Cam timings. More to come..

Brought the bike out to the Ranch for further evaluation...

My MAJ mod was probably not very functional.. Turns out the stock MAJ is a jet with a .1" opening that tapers to something very small.. All I actually did was to reduce that .1" opening to .05" ... I have removed the mod..

The DGR and FMF system continue to perform as the charts show. On the road, the FMF is the only way to go as it pulls so hard in the upper RPM ranges.. Each WOT gear shift keeps the engine in the FMF's sweet spot - so it just keeps pulling hard after every shift..
On the road, the DGR requires short shifting ( @8.5k ) - but the HP available at these higher RPMs is, of course, less than with FMFs'... It simply doesn't give the same pull when running through the gears @ WOT as the FMF. Also, top speed is probably less with the DGR.

Off road is purely owners choice - I ride fast and would keep the FMF.. If I was taking a gal on back to the trails and then putting around offroad , the DGR is the only way to go- it makes up to 2hp more over the FMF below 6.5k and that is a big TRQ difference. The TRQ @4.9k would take 6.5k with the FMF..

There is probably much more power to be found with the DGR - AFR's are still too lean for it to show its' true potential..
There is probably some power to be found up high with the FMF -AFR's are still too lean up high for best power..

It seems that every portion of the AFR curves that are above 13:1 are costing power. Unfortunately there is a lot of "above 13:1" still..

My MAJ mod was probably not very functional.. Turns out the stock MAJ is a jet with a .1" opening that tapers to something very small.. All I actually did was to reduce that .1" opening to .05" ... I have removed the mod..

Since I'm looking at doing something similar to my Keihin I'll reopen this old MAJ mod subject and ask why you didn't go to a smaller MAJ after finding out the inner passageway was smaller than the part that's visible?

On my particular Keihin the part that's sticking out into the air stream at the bottom of the carb inlet barely accepts a 2mm drill bit, but the inner passage is much smaller; only allowing jet a cleaning rod to slip all the way up to the needle jet. It'd seem though that eventually going small enough with a MAJ would at some point begin to restrict MAJ inlet air and yield a richer high rpm mix.

I have to go out once the weather clears and check the WOT a/f numbers to see if the reading drifts rich or lean at high rpm

Reducing the MAJ orifice size is tuning the AF toward richness in the emulsion tube - therefore richer AFR at all main fueling circuit ops. Problem I had was that there was no info - that I could find - on what the tuning method should be. I know the tuning method for enriching the AF with progressively larger main jets. And as far as I can tell, the end results would be identical - so I went with what is known, larger main jets until AFR is charted(proven) to be correct.

OK, I'll see if my a/f is drifting one way or the other as rpms climb and go from there.

Compounding the end result is the fact that cranking it open at mid to low rpm-which removes the needle taper effects (since it's now at one position/WOT) vs opening throttle more and more kind of places all the work load on the main jet. Meaning what's too rich at less than WOT may be perfect at high rpm,

- One tuner's article suggests removing the main jet altogether for testing, saying the bike should run cleanly up to about 3/4 throttle as you open it progressively (if the needle position is correct) before the lack of a mj has it stumbling.