Baseline Conditions:
I purchased my "pre-owned" VTR1000F Super Hawk on Thanksgiving day 1997 with 1,387 miles on the clock. Prior to the initial sale, the Dealer had made the following modifications:
Here are the results of my baseline dyno run:
Factory Jet Kit:
The next step in the evolution of my carburetor calibration was the installation of a FactoryTM jet kit. Although I was pretty pleased with my Baseline dyno numbers, I found the Factory jet kit on ebay for $40.00 (as opposed to almost $100.00 retail), so I thought I'd give it a try. I attempted to get the Factory kit dialed in from May through September 2000 but was never able to get clean carburetion through the entire rev range. Tuning the top end and the botton end are easy, but getting the midrange and especially the transition from the idle circuit to the midrange circuit twas quite difficult.
As part of the experimentation with the Factory kit, I removed the air box inlet snorkel and internal baffle. Common discussion on the VTR email list indicates that this change is not recommended due to the reported finicky nature of the huge (48mm) carburetors. However, I thought if the reduced restriction could be adequately compensated with jetting changes, it would ultimately improve performance. The snorkel portion of this mod is readily reversible, just put it back. But removal of the internal baffle is another matter. This entails cutting of a ridge/flap which is integrally molded into the OE air filter panel. Therefore, reversal of this change requires procurement of a new air filter.
Here is the last iteration of settings for the Factory kit...
This combination resulted in the following dyno numbers, shown compared to the baseline condition:
Note that the lines for the modified configuration are broken. This is because the dyno rpm sensor was not working properly when I made the run. As a result the data was acquired against wheel speed (mph) instead of rpm. In order to compare to the previous/baseline data which was measured relative to rpm, I had to set up a conversion in MS Excel to turn wheel speed into engine rpm. The breaks in the data are due to gaps produced in the conversion and rounding off of values.
On the plus side, removing the inlet restrictions resulted in a very noticeable improvement in throttle response. The bike literally LEAPS forward any time the throttle is whacked open. However, this improvement is not measurable on the dyno since the dyno test is performed at a constant wide open throttle setting.
The down side to the Factory kit was a very stubborn lower mid-range lean misfire. The misfire exists right at the transition from the idle circuit to the needles at about 3,500 - 4,000 rpm. Of course, this is exactly the rev range where I do about 98% of my riding.
Raising the needles further pushes the mixture over the edge of richness and makes it run like crap through the entire midrange. So, I attempted to compensate by richening the idle circuit way beyond optimum in an effort to get rid of the misfire at transition. Based on my experiments to date, I've drawn the conclusion that the Factory kit needle profile just doesn't cut it on the Super Hawk.
Ultimately the dyno curves for the final FactoryTM configuration showed a gain in midrange power from 4,600 rpm to about 5,500 rpm and then a 5 bhp loss from 5,500 up to redline. So, it would appear that the top end is still not right for the modified airbox. Although I've read elsewhere on the 'web that other VTR owners who have attempted airbox mods have gone to #190/#195 main jets, there was significant evidence of black soot in the exhaust at redline. Thus indicating the top end was excessively rich.
Jardine RT-One pipe, Dynojet jet kit and K&N air filter:
My next iteration toward performance nirvana was removal of the Factory kit and installation of a Jardine RT-One high mount slip-on pipe and a Dyno Jet kit and K&N air filter, which I received as a gift from my Brothers in-law for Christmas 2000 (thank you Alan & Rick). My experiences in attempting to procure the Jardine pipe were not completely positive as described on my VTR 'page. But once I got it, I was quite pleased with it's looks, quality and fit-up.
The needles provided with the Dyno Jet kit have a more gradual taper than either the Honda OE needles or the Factory needles.
Also, the Dyno Jet needles have one more adjustment notch than the Factory needles (Honda OE needles have no adjustment notches). The combination of more gradual taper and greater adjustment range have solved the idle to mid-range transition problems encountered with the FactoryTM kit. Finally, the Dyno Jet kit includes softer slide return springs has you drill an additional "lift" hole in the carb slide to further improve throttle response. After a few seat-o-the pants adjustment cycles, I settled on the following settings for the Dyno Jet kit and went for another dyno run:
A comparison of the Dyno Jet kit to the baseline looks something like this:
...which shows a mid-range gain from 3,800 rpm to 5,800 rpm, but the top-end was still down from baseline (101.3 bhp vs. 103.7 bhp), but not so bad as with the Factory kit. Although the top-end was too rich with the Factory kit and a clean OE air filter, I have a sneaking suspicion that the K&N filter is causing a lean top-end with the Dyno Jet kit.
Conclusions as of May 2001:
Idle mixture screw adjstment:
A note on the convenience of VTR idle mixture screw adjustment... it is very nearly impossible to do with the carbs on the bike. The Honda Service Manual provides comprehensive instructions for idle mixture adjustment, that should take no longer than a couple minutes. In fact I had accomplished the adjustment in only a few minutes on my old VFRs. However, things are different on the VTR. The VTR idle mixture screws point straight down from the carb body. The problem with this is that it puts them right in the middle of the very congested vee between the cylinders. This area also serves as home to the radiator overflow tank and some medium sized coolant hoses that feed the carburetor heaters. So, there is absolutely no way to reach a hand in there to turn idle mixture screws, even when the bike is cold, let alone when it is hot (as it should be when you do the adjustment.) Honda does list the part number for a pilot screw adjustment wrench, but the local dealer wants $106.00 for it, too much for me.
Speedometer error:
While on the dyno and since the VTR speedometer is driven by the transmission, (rather than the front wheel) we also did a speedometer calibration run. This run verified what all the VTR email listers have been saying about the optimism of their speedometers. I've included a table showing the indicated speed, actual speed and % error for my speedometer from an indicated 50 mph to 130 mph. Now that I have changed the countershaft sprocket, the speedo reading is another 6% (total of 16%) off from actual.
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If anyone out there resides in the Greater New england area and would like to Dyno their bike, contact:
Fred Eno of Eno Enterprises163 Elm Ridge Road, Pawcatuck, Ct 06379; (888) 214-2145, www.drdyno.com
For a minimum of $600 he will trailer the dyno unit almost anywhere in the region. You will also find him at the region's major motorcycling events (i.e. Marcus Dairy Super Sundays and several other events.) and the his website has an up to date calendar of where he will be on any given weekend