Drilling Slides and Reversing the Process.

[TC]

Rey, I am not trying to discount the unfortunate experience that MCN had with their 650cc Hawk ... and I certainly believe them when they state that from their article ....   "Remember that the all-new GSX-R 750 has computer-controlled slide venting.  Our test indicates why.  Smaller vents will give better off-idle response, and larger vents give better response at high rpm.  Now we know why Suzuki went to all the bother."   .... as I think this might be true with everything else remaining stock ..... and I am not attempting to challenge their expertise or that of their dyno people with this response or to attack you in any way ... I am only pointing out that I think it is unfair to make such a statement without a lot of qualification. Additionally, if Suzuki "went to the bother" to computerize their slide opening the computer must be monitoring something beside screams or foul language from the operator like ... airflow ... vacuum ... etc .... The slide simply reflects the standing pressure difference between the area in front of the slide and a hole located below the throttle plate ... it's retraction is an indication of increased airflow.   I wonder however if the 650cc Hawk kit came with lighter springs as the DSP044 springs that come with the Vmax Dynojet kits are 2 1/2 inches shorter than stock and only offer 1.5 grams compression resistance as opposed to 5 grams for the stockers, (more than three times less effort to compress the slides and the needle it is pulling on .... Thanks to Patrick Ahern for measuring the tension on these guys ... ) .... IMHO ... I think that everyone knows that none of the above would have any affect for top end horse power .... as once the slides are open you are running on the main jet and how much air you can get into the top of the carb, (while still being able to create enough vacuum to pull some fuel along with it). The size of the slide vent hole works against the #2 purge jet, (which is an air vent located below the throttle plate), to overcome the spring tension and open the slide.   As far as the DynoJet arrangement improving performance ... I don't think I would bother if I wasn't opening up the air intake on the bike in the bargain .... as airflow potential is maxed out in stock condition with the "Y" in place ... despite there being a K&N, UNI or no filter in the air box, (thanks to Terry Hayden for measuring the "suck" resistance of these airbox combinations). If no additional air comes in the front door ... you can add all the exhaust systems in the world and you would not likely see more than about 4 RWHP ... because despite what gets exhausted .... you can't make that much more HP without getting more air into the engine and the gains in efficiency from a superior exhaust would be greatly suppressed.   On the other hand ... take the "Y" off the Vmax and don't do anything else and see where your low end response goes ... check the mid-range on the dyno .... As you well know it is not uncommon for some of it to disappear but often give you an additional horse on the top. Sooooooo ... we didn't change any slide vent holes ... where did it go ?? Should I make the slide hole "smaller" to counteract this modification ... will I get it back ?? ... I think not ....... Was I flowing more air ?? Of course I was !! That was reflected in the gain at the top end ........ Soooooooo ... the easy way to fix that is to put a washer under the needle and make sure it is retracted a little more than it used to be for the same position of the slide ... and wala !!! my bottom end comes back .... annnnnnnnddddd I get to keep the gain on the top .... Clearly, (and I am not trying to be funny here), we did not lose our low-mid range in this scenario because of changing the the size of the slide hole ... we lost it because we did not adjust our needle properly to provide an optimal amount of fuel within this RPM range ... and guess what .... on the top end we gained because it didn't care about the needles ... at that point they were fully retracted, (of course a main jet adjustment there might have given us another couple of horseys).   Clearly ... the instructions for both the DynoJet kits have everyone setting the needles too rich for default but once they are set up properly they do infact provide whomping throttle response compared to a stock setup, (IMHO). I don't know if the carbs on the Hawk have bypass holes either, (pilot mixture holes on top of the throttle plate), as the Vmax does and these along with what is coming out of the mixture screw holes, (underneath the throttle plate), and what ever escapes around the needles is what the bike is running on when we go off-idle. IMHO if someone is tuning a bike and depends too much on slide movement to save their butt on an off-idle condition then they are asking for trouble and should be making additional adjustments in their pilot circuit. If they are looking to for more fuel when they womp on the throttle they need to give the thing a little more needle or remove some of the resistance from the slide operation. Also ... IMHO .. if someone is looking to launch themselves over a parked car when they peg the throttle ... these are the kits that will give you the ability to do it .... because the slides will open ... quickly ... Of course this presents another opportunity to mis-tune by using as much needle with this slide arrangement as you are used to with stock vent holes and stock springs .... there is just going to be too much fuel dumping in there and responsiveness will suffer as a result .... also on 4500 RPM cruising you will foul your plugs in short order because you will be running entirely too rich ........   Sorry for the length here ... you guys can attack now ... sigh ..... NO .. I don't work for Dynojet or Redline oil ... campbell              ----- Original Message ----- From: Rey Kirkman To: V-MAX TECH LIST Sent: Tuesday, March 07, 2000 12:41 PM Subject: Re: Drilling Slides and Reversing the Process. I reversed my Dynojet slide holes by filling the holes with J.B. Weld.  I redrilled holes adjacent to the filled holes.  There was an article in Motorcycle Consumer News by Dave Searle, dated May 1996 a while back which addressed drilling of slides.  The bike they tested was Honda 650cc Hawk.  After drilling the slides and installing the rest of the components, throttle response was off.  Following are some interesting quotes from the article:       "Resigned that we must have done something wrong, we scratched the head of Joe Youkhan, the dyno operator, who'd had considerable experience with these kits.  Regarding the sluggish throttle response, he said that he doesn't ordinarily drill slides as suggested unless the bike  is really intended for the racetrack, because which throttle response at high rpm is enhanced, it is worsened at low rpm...Hmmm?  Back at the shop, we called Two Brothers Racing to see if they had any tips for us, assuming their extensive Hawk knowledge would provide the answer.  We were told, 'We don't sell the Dynojet kits, because nobody can get them to work.' "       "We called back the folks at K&N, which had provided the kit.  Acknowledging the company's reputation for quality and expressing satisfaction with other Dynojet installations we'd done, we gave them our results.  We also relayed the remarks we'd received from the dyno operator and Two Brothers.  They said their dyno comparison showed a gain of nearly five horsepower and offered to send another kit although our description of the needle dimensions seemed to indicate we had gotten the correct parts.  We were told however, as Joe suggested, that drilling the slides would hurt off-idle response but that the carbs would reach full throttle soon and therefore gave an acceleration advantage in spite of the derivability problem.  We were told the drilling does not actually influence horsepower, so we resolved to leave the slide holes alone on the next attempt.  Remember that the all-new GSX-R 750 has computer-controlled slide venting.  Our test indicates why.  Smaller vents will give better off-idle response, and larger vents give better response at high rpm.  Now we know why Suzuki went to all the bother.   MCN used a 0.109" drill to redrill the holes to stock size.   In November '96 in response to a query of a Yamaha FJ 1200 owner who wanted to undrill his slides, MCN called Yamaha.  There is no Yamaha spec for size of slide holes.  Yamaha suggested calling Mikuni, and Mikuni said the sizing had been worked out in Japan in concert with Yamaha engineers.  Dynojet's tech rep said they have information back to '91 models, but suggested most stock holes are in the neighborhood of 0.110".  A #35 drill is 0.110", and a 7/64 drill measures 0.1094"   Rey Kirkman ----- Original Message ----- From: P. Kuyper To: V-MAX TECH LIST Sent: Tuesday, March 07, 2000 8:08 AM Subject: RE: Going back to Stock Jets. If the slides are drilled out, it CAN be reversed.   Take some good 2-component glue. Close the hole with the glue and let it dry thoroughly. Drill in the original size holes again. However, at the moment I do not know the size. Anyone??   Patrick Kuyper Vmax Club Holland The Netherlands -----Original Message-----