 Re: Kenny & the Jets...
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Joined: Jul 2008
Posts: 1,440
Learned Hand
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Learned Hand
Joined: Jul 2008
Posts: 1,440 |
It sounds to me like the springs are opening just barely too quick. That temporary flat spot might disappear altogether when the weather warms up. Another solution if you're willing to compromise on perfect F/A (but not so much on performance) is to over-richen the idle a little. You might have to change plugs more frequently, but a larger pilot jet would probably push a richer mixture into the transition area and solve the problem. It's easy enough to try.
'08 America Blue/White; Custom Headlamps, Custom Lowers, Clearview 20", Bafflectomy
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Re: Kenny & the Jets...
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Joined: Feb 2008
Posts: 2,671 Likes: 15
Loquacious
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OP
Loquacious
Joined: Feb 2008
Posts: 2,671 Likes: 15 |
Quote:
It sounds to me like the springs are opening just barely too quick...a larger pilot jet would probably push a richer mixture into the transition area and solve the problem. It's easy enough to try.
Yes, we're on the same frequency about the springs & pilot jets. I'll probably try 45's just for grins. It could be enough for my 865...
With the 42's & the pilot screws 2 turns out it is just a tad rich at idle. I'm thinking that the pilot screws in a bit will compensate for the idle mixture (if necessary) & a fatter pilot will improve the transition.
FWIW the peak (uncorrected) dyno numbers were 54.62 HP & 51.23 Torque, respectively; that was with a relatively "cold" motor on the run with the current carb tune. There was probably a bit more to be had with a warmer motor, but time was short. I'm much more interested in achieving favorable A/F under load than I am with the peak power & torque #'s anyhow.
The 865's don't make anywhere near the HP of a good 790, but they do make better torque where it is most useful on the street. Of course a BB with good cams, pipes & carbs will blow both away. That said, I want to optimize what I have & enjoy it for awhile before I do a BB.
Given the snow & ice outside now, the tuning will have to wait.
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Re: Kenny & the Jets...
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Joined: Jul 2008
Posts: 1,440
Learned Hand
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Learned Hand
Joined: Jul 2008
Posts: 1,440 |
Quote:
The 865's don't make anywhere near the HP of a good 790, but they do make better torque where it is most useful on the street. Of course a BB with good cams, pipes & carbs will blow both away.
FWIW, my experience building motors and vehicles is probably the opposite of most guys my age. I started with bikes in the late '60s at a time when my buddies were hot rodding cars. After a few years though, I wanted more speed. Even in lower gears, the better hot rods would pull ahead, and I really disliked the inability to accelerate well at near-triple-digit speeds. That pushed me into four wheels, and over the years, I became a fanatical builder/tuner of big-block street 'Vettes. I quickly discovered that I could dust off any bike I came across, including my old favorites - the Honda 750 and Kawa 900. Sometimes they could pull a few feet in front from a standing start, but it was all over by the time we hit 10-15 MPH. HD riders were the worst at accepting this. They would try over and over, every redlight, absolutely unable to deal with it. Curves were even worse for the bikes, none of which had a chance on a winding road. In fact, I stopped racing against bikes when a guy on a Harley spilled it behind me, trying to keep up on a city curve in Dallas. This was all before the days of crotch rockets, of course. It would take much more work and money to build something competitive nowadays.
Anyway, the point is that I went through the faster-than-thou phase years ago, and I have no interest in doing it again, especially on a bike. There are times I'd like a little more ooomph at highway speeds, but not at the expense of low speed tractibility. That's why I said in a different thread that I would gladly trade my bike for a 1200cc America. Other than that, I like these bikes, and mine does just about everything I bought it for. I suspect we're on the same page in that respect. 
'08 America Blue/White; Custom Headlamps, Custom Lowers, Clearview 20", Bafflectomy
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Re: Kenny & the Jets...
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Joined: Feb 2007
Posts: 23,219 Likes: 61
Fe Butt
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Fe Butt
Joined: Feb 2007
Posts: 23,219 Likes: 61 |
I think many of us are on that page. I just want my bike to be jetted for good A/F mix for the sake of the engine not power or speed. It does run better in that department with it jetted right but I am not interested in big bore or any of that until the rebuild is needed due to wear. At that point I may do the stroker big bore since I will go through the whole engine anyway instead of just doing a top end. Basicly I just want my bike to run right, be dependable, and be fun. I have all that now so at this point I mostly just ride it and the occasional cosmetic tweek.
I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!
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Re: Kenny & the Jets...
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Joined: Feb 2008
Posts: 2,671 Likes: 15
Loquacious
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OP
Loquacious
Joined: Feb 2008
Posts: 2,671 Likes: 15 |
Latest iteration is 152 mains, 45 pilots, stock needles with 2 shims, & pilots set 1&7/8 turns out.
I road tested this setup today, conditions were low 40's F, clear & dry. Any off-throttle hesitation that may have been there is gone with the 45 pilots. It feels really strong in the midrange, & is perhaps a touch rich at idle (perhaps another quarter turn in on the screws would handle that).
I plan to get the bike to the dyno for a confirmation & final tune run as my schedule & the weather allows. It will be interesting to see how the 45 pilot impacts the A/F curve & whether or not it would do better with only 1 shim.
We'll see, stay tuned.
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Re: Kenny & the Jets...
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Joined: Feb 2008
Posts: 2,671 Likes: 15
Loquacious
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OP
Loquacious
Joined: Feb 2008
Posts: 2,671 Likes: 15 |
The weather, my work schedule, & various family commitments have really cut into my riding & tuning time. I did get a few moments to have the bike out today & test my latest pilot screw settings. Clear & dry with temps about 41 F. With 152 mains, Kwacker GPZ vacuum springs, 45 pilots, stock needles with 2 shims, & pilot screws set 3/4 out it is a very satisfying ride from the saddle. It now idles smoothly & feels great everywhere else. The midrange feels particularly great. I plan to get it back to the dyno sometime within the next few weeks for confirmation. The front end now feels great too, with the 10mm longer PVC spacers for the standard length Progressive fork springs, complemented nicely by the Progressive standard length 412 HD rear shocks. Did I mention that I love this bike...  
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Re: Kenny & the Jets...
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Joined: Feb 2008
Posts: 2,671 Likes: 15
Loquacious
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OP
Loquacious
Joined: Feb 2008
Posts: 2,671 Likes: 15 |
Back to the dyno today, basically made the same power as last time.
Interesting though, is that the OEM 152 Keihin mains were actually slightly more rich (13.0 A/F from 5000 - 6800) than the aftermarket 152.5's that were in for the last run (they were 13.4 A/F over the same RPM band)...
It was still a touch rich at idle according to the dynos A/F meter, so I leaned the air screws out to 5/8 turns out. The A/F ratio at idle was basically the same on both the right & left carbs, FWIW.
I also installed side-gapped/knife-edged Autolite 4163 plugs for the latest dyno run. I don't think they made any difference whatsoever with regard to power. IMO stock NGK's are the best plug for this application; no fancy side-gapping needed or even desired.
Now it's all about minor fine-tuning for optimal drivability.
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