The cold Minnesota Winter has spawned many garage projects for me over the years. Some of them worked out, some didn't. But the quest for improvement always continues. I've been running the Uni pre-filter, with H2W jetting for the last year, and have been happy enough with it, but the restriction in this setup is apparent by the amount of steps down the main jets are from stock. I decided to look closer at the Original snorkel versus the Uni filter to see if the restriction was just from the foam filter media, or something else. I measured the air inlet of the snorkel at about 86 x 30mm, with a calculated area of around 2580 sq/mm. The opening at the airbox is about 86 x 44mm, with an area of about 3784 sq/mm. The actual air inlet of the Uni-Filter is only about 65 x 35mm, with an area of only 2275 sq/mm. It would seem the air inlet itself offers a greater restriction than the stock snorkel, so the foam might not be as much of a factor as you might think. I decided to trim the opening to a larger size, just to see if engine response might improve at higher RPM. The rubber base/air inlet is some pretty thick rubber, so I got a fresh razor blade ready to start trimming- The white line is about where the original opening is. It's not pretty, but then it doesn't really have to be- I ended up with an opening that now measures 80 x 40mm, for an area of about 3200 sq/mm, an increase of around 40%. With the foam restriction factored in, any actual flow increase might be far less. Maybe even 0%, who knows? I was also concerned with how the CDI unit crowded the Uni-filter. It seemed like a big chunk of the filter area was basically unusable, so I took the mounting bracket out, and zip-tied the CDI to the side in the steering head area, which leaves plenty of room around the filter- We'll see if any re-jetting is needed when I can actually ride this thing again. April, maybe. Two Whole Months. Now, what's next?
I was thinking the same thing. The only time I'd probably use the pre-pre is in miles and miles of fesh-fesh. And I ain't good enough to try that on the 990 or any other bike.
I see where you are coming from brother, but you have got it all wrong (1) If you want to de-restrict the inlet tract then ditch the prefilter, then the airbox, then the carbes. Fit a set of FCR's with uni filter 150mm pods. You can get them with TPS fitting. (2) If you want to have a bit more up top fit 07 SD Cams. (3) What you have failed to realize is that you are dealing with Constant Velocity carbs "CV" A simple, although not totally accurate description, but easy to comprehend, description is thus :- Your hand is connected through a cable to a butterfly valve. Opening it creates a "pull" a say vacuum on a tube conected to a chamber above the carb. This chamber has a diaphragm connected to a slide (Throttle Slide similar to any normal carby). So when you pull the throttle cable the more restrictions to the air flow translate in that diaphragm chamber as more vacuum = Quicker throttle response. The slide moves faster = the front wheel lifts. (4) Jetting........ The reason you go down in jet size is because you have more "pull" on those jets by fitting the pre-filter = the same size gives more fuel. In 2005 a whole bunch of us set out to improve the throttle response of these 950 bikes. I made the first pre-filter as we know it. I got the idea from Mioni. 2HP (Melbourne Victoria) took the idea to Uni Filter (Australia). Widebands were used...... and still we struggled. Autostream (Melbourne Victoria) described one day what a leak jet was...... for me this was the turning point. Ken H2W has worked tirelessly to market a kit that works............ you can not improve on it for this CV set up! People from the States, from England, from Italy, from Australia all worked together. Every avenue was explored, Factory Pro needles...... everything was tried. Hopefully you haven't done any damage............... If you must improve things you must get a wideband....... You can not tune without one! Our KTM is like a WRC Rally car ........good at everything, but it is no Formula one car or Moto GP bike. Imagine riding Cassey's Honda on some single track
Thanks for the History lesson, K2m! I think you misunderstand my intentions, however. I'm not looking for some kind of huge gain in HP. I chose the Uni because the bike is ridden off-road most of the time, and I got tired of cleaning sand out of the airbox. Pyndon showed the Uni could be improved upon with his large-diameter K&N pre-filter. He claims to offer some improvement in top-end pull from the increased air flow. I simply noticed how small the hole in the Uni filter is, compared to the opening in the airbox it fits into, and wondered if it could be improved upon. I found the improvement in throttle response on my DR650 was quite dramatic, after opening up the airbox, and altering the jetting to match. I think I understand the principles behind the operation of CV carbs, and various configurations of internal combustion engines, as well, having been a professional Automotive Technician for over 40 years. I've also modified and raced my own motorcycles during that time, resulting in more trophies than I care to remember, both on and off-road. But, thanks for your concern.
My real reason for the history lesson was to warn others about the consequences of following you blindly in to this mod. Actually your headed in a similar direction to the one I took. If you look at my pre-filter you will notice how open it is. The problem is that Ken tuned his kit with the uni filter as it is supplied. I know just how sensitive these machines are to air box/filter mods, and really you need a wideband. By contrast stick on any muffler you want leave it alone. Only if you fit an extractor should you re jet. The biggest drawback to the uni is its size. I clogs to easy. I was in the process of fixing this when that other Ken turned up with FCR's and I was immediately distracted I like Pydon. He is a good mechanic and a great asset to the OC. His filter, if you trust K&N's is by far the best option...... But the advise to leave the jetting stock is not correct.,....... To me it is unfinished business. It needs H2w's wideband work to finish it of. You can blame Powercell for this solution not being part of the choices............ Him and his FCR's
+1 16/45 gearing and judicious right hand returns 45+ mpg, nearly independent of terrain, fuel or elevation. Runs great @ 112/50+c and never out of 3rd gear "terrain". Installed FlexJets and never adjusted them from 5000' to sea level up to 15,400' - it started, ran, and idled perfectly. I run a Filterskins sock on the UNI and . . . Can't imagine how it could be better and theoretically speaking would prefer FI. Went from Frankfurt to Ulaan Bator via the dusty 'Stans on two Filterskins and stock paper filter looks great. Ken (H2W) has done not just all the work but a remarkable piece of work. Kurt
I think the theory of 'more vacuum' = 'better throttle response' is flawed. The reason I say so is my experience of the 3x3 mod on the DRZ400S. The story behind it is that you take the stock drz and open up the airbox to a 3x3 inches size out of approximately 1x3 with the appropriate jetting. Then the bike is night & day compared to stock in terms of throttle response. 'Appropriate jetting' means a dynojet kit which also contains a new spring for the slide of the stock CV carb.
Changing the cab slide spring ?????? The only way your argument holds true is by leaving the original spring in. Obviously the bikes design is flawed as there is to much restriction. Probably to keep induction noise down. I think if there was a need for this someone would produce it for the 950 I'm amazed at the success of this new top foam filter. I guess the limiting factor will be lack of air box in river crossings. FCRs are the best way to go. Worth every cent. It's your hand that controls the slide, not the vacuum. If you change the springs on a 950's CVs then that you would change everything.
The stock vs DJ spring for the drz seem identical to the 'hand test'. Maybe it is slightly softer, but I couldn't tell the difference. At the end of the day though, it does seem that restriction is not necessary for throttle response, would you agree on that? Another example is the CPR as you said as well as the pod filter experiments of Navin. FCRs should be great but pricey and I wouldn't want to live with their quirks. It seems to me that next step after H2W (for the price) is a DNA filter + mains and/or the pods.
the thing is with cd /su type carbs is the weight of the spring on the plunger also changes the fuel curve of the carby the heavyer the spring the more of draw on the main independent of the needle pos
Somebody on a dutch forum removed his FCR's from his 950SM. Because there was very little improvement compared with the standard CV carbs and MH box he had before. Only more fuel use.....
Seems like I read somewhere that the vacuum differential between outside and in the airbox are a key factor in the operation of the stock CV carbs. From what I understood the restriction of the UNI is actually helpful to get the carbs to open more quickly and/or fully, as the slides are vacuum operated. Maybe I didn't get the gist of it, but that was how I remember the operation and choice of this filter being explained. If this is the case, the mod by the OP is just moving toward allowing the airflow that the OEM design had. Whether this will affect the CV slide in a positive or negative way can probably only be proven on a dyno. As for the comparison to the DRZ, the S model in the US is de-tuned to meet both noise and emissions requirements. Intake restriction is a part of that. (the S also has a smaller diameter header pipe and lower compression engine) The off-road only E model comes with a flat-slide carb and an easily removable snorkel that leaves a hole size similar to that the S model folks have adopted as the standard performance mod. I don't think this can be usefully referenced for the 950. It like apples being compared to Orange.
ha, I doubt he had them tuned right then. There's a reason all the race bikes use FCR's, response and power.
I had assumed we were talking about the spring inside the slide. Changing that would have a big effect on jetting. The spring you feel with your hand would be on the outside of the butterfly valve. If I was running C/V's I would leave it alone after fitting a H2W jet kit with pre filter. I recon, and I speculate, Pydons K&N with a dust sock, and a H2w jet kit would be as good as it could get. (It was good enough for Mioni). I have found that Uni and K&N can be swapped without changing the jetting, which is interesting Pods on CV's ........ I would not do it.
For those who may be interested I have been building an air box for my FCRs on my new project "KTM 950 Trail Bike" I figured I might as well build a "Forced" cold air induction. My intakes will be either side of my oil cooler. Through flex hose into the fuel tank. Should be very effective, and still leaves the carbs exposed. This engine is WAY to beautiful to hide under a fuel tank
k2m, it is the slide spring I mean, not the return butterfly spring! MotoTex, that is exactly what I thought too. That vacuum is necessary and it does make sense if you think about it. However, the drz example is not to be dismissed that easily IMHO. It has a similar CV carb to the 950 and benefits from opening up the airbox as well as a free-er flow filter (with the appropriate jetting). Mine had a DNA. If the response on the drz improves, then why not on the 950? Unfortunately (if you can say that!) I'm on holidays right now, so I cannot experiment, but in a few weeks time I will try to remove the prefilter on my SE, keep the H2W bottom jetting and put back the stock main jets with the snorkel. If that leads to similar low end grant plus better top end power, then it will be a success.
ok so i tried the h2w settings with the 80 iaj and the dna filter and snorkle at sea level. It was ok with this, not great though. I found some 100 iajs and put them in for kicks and nowit is really good with 175 main jets and 2 turns out. Smooth and quick. It pops a little but a quarter turn further out and it gets flat , the flex jets are the best