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H2 flatspot issues
http://www.kawi2strokes.com/forum/viewtopic.php?f=16&t=9044		 Page 15 of 15
Author:  h2b780 [ Wed Oct 14, 2015 12:23 am ]
Post subject:  Re: H2 flatspot issues
Have done some testruns with uncut pistons, and low/mid has improved. But still pretty lame until pipe's kick in! Topend stayed the same btw.!?
Test's was done with the 16:1 heads and VP109 racefuel and it will still deto some!!??
Author:  AER005 [ Fri Oct 16, 2015 2:58 am ]
Post subject:  Re: H2 flatspot issues
Ha Rod If Theres beer involved im in , are you going to the is in feb ?????
Author:  RODH2 [ Fri Oct 16, 2015 6:21 am ]
Post subject:  Re: H2 flatspot issues
Caught that one.... yes, for Feb for I.C.. and Al, your neutral switch is posted.....! :thumbup: (Good thread hijack, or what...!!...) Don't cut pistons for a street bike.......!
Author:  motometal [ Sun Nov 22, 2015 8:17 pm ]
Post subject:  Re: H2 flatspot issues
With some of the discussion on return waves, at certain speeds is this really describing double carburetion? What I believe happens on my bike from 4000-5000 is this, which is likely made worse by the piston cut. Leaning the needle circuit helps the bog but you can reach a situation where it's still too rich for the bog range, but lean for the powerband. This is illustrated by momentary pinging when letting off the throttle gradually at high engine speed.

I wish there was a practical way to provide more of a column of air on the filter side of the carb. The frame location complicates things. When my bike was closer to stock, it ran noticeably smoother in the midrange with the factory airbox vs. pods.

Also...how much of an improvement is gained from milling the intake surfaces perpendicular on the cylinders? Some do it, some don't. A more direct flow path but effectively even shorter tract.
Author:  Ja-Moo [ Sun Nov 22, 2015 9:12 pm ]
Post subject:  Re: H2 flatspot issues
There is "some" relation, but it is really an overlap of systems. The longer the intake timing (piston skirt cutting) the more crankcase pressure is open to the intake port, and longer duration, blowing the mixture backwards through the carb (which is picking up fuel) or double carburation. And there is also the point, 5000 ish rpm where the systems come into working in unison, and that is a stumbling point in 2 and 4 stroke motors. Where in 2 strokes the pipe is now helping pull the mixtures the motor instead of the motor pumping the mixture through. So both of these are in play.

As far as machining the intake port, short helps at higher rpm as the mixture has a shorter path, and less compress-ability. Short and long have both worked well on drag motors, but I don't see the short intake length helping on a lower rpm street motor. And probably a minor detriment.
Author:  Neville Lush [ Mon Nov 23, 2015 8:23 pm ]
Post subject:  Re: H2 flatspot issues
If the inlet tract is modified as described the powerband will commence at a lower rpm and continue for more rpm, widening the power spread. The bike may idle worse due to the carb angle.
Author:  motometal [ Thu Nov 26, 2015 8:55 am ]
Post subject:  Re: H2 flatspot issues
Thanks for the replies, guys. I was thinking the angle was more of a change than the shortening. Would be easy enough to lengthen with spacers, if that was desired. The milling perpendicular is a popular mod, but I wasn't sure if this was usually for performance or carb clearance. My 34s barely fit, actually I had to machine out a pocket for the bowl nut...so I suspect fitting bigger carbs would require the milling on the cylinders.

Regarding the operation of the carbs at an angle, the way many of us fit a smaller wheel and longer shocks makes this effect even more pronounced. I suppose float level becomes more critical.
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