Well Paul I did some looking into the math to try and figure it out. I found that your engine can flow a max of 16.2 CFM at 85% VE. The troubles is figuring out the flow rate of metric carb sizes. I did find this: http://www.rcuniverse.com/forum/engine-conversions-92/839599-formula-calculating-carb-size.html . According to that post your 27mm carb is right sized for WOT @ 22k RPM. So I'd check out the aprilla forum and find what jetting to use on that setup with a free flowing filter and exhaust.
Allen Thomas On Jan 4, 2015 12:01 AM, "paul annen" <[email protected]> wrote: > All good concerns, this engine is set up to take a max 27mm carb and turn > 22 rpm (love the 2 strokes!) Not sure of the math on that but I'm sure the > flow from the twin 7mm is much less. > > This scooter will do 102 mph with the 27mm carb, performance exaust, 80cc > "big bore" kit, and a change in the weights and springs of the cv > transmission. That does put it at the 22k rpm... > > I swear Aprilia is itilian for "hey y ' all watch this!" > On Jan 3, 2015 8:02 AM, "Allen Thomas" <[email protected]> wrote: > >> In my experience with street racing the cfm flow of your carbs can >> greatly affect performance both good and bad. For instance on a 350ci motor >> a holly 650 will out perform a 750 in all but the most highly built 1/4 >> mule race engines. Because a 350ci motor can't flow that many cfm unless it >> is spinning above 8k rpm. So on a door slammer going with the smaller carb >> will give much better throttle response. So my advice is to do the math. >> Figure out how many cfm your motor can flow at the desired rpm then figure >> out what mm carb is appropriate. Too small of a carb and you will restrict >> top end flow and loose top speed. Also there can be a lot gained on those >> type of setups by playing with the pullies and weights for the CV setup. I >> like the leaf blower idea personally. Positive pressure negates consernes >> about carb sizes. Just be sure to jet for it and retard the ignition timing. >> >> Allen Thomas >> On Jan 2, 2015 7:07 PM, "paul annen" <[email protected]> wrote: >> >>> Ok, question to all of my engineer friends. >>> >>> So, I want to increase the performance of my 99 Aprilia sr50. Factory it >>> comes with a 7mm carb, you can go up to 19mm before an exaust mod is >>> needed. Aftermarket carbs are expencive, but factory ones are cheap.... my >>> question is this, is there any issues with putting 2 (or 3) factory carbs >>> on a manifold setup (yes, I would have some fabrication work to get the >>> linkage to work right) for this 50cc single cylinder engine? >>> >>> Later possible upgrades include >>> more carbs (it will handle up to 27mm) >>> Performance exaust >>> Electric turbo (12v leaf blower puts out 10 times the volume I need, but >>> only would give about 8 pounds of boost) >>> >>> Thoughts? Questions? Concerns? >>> >>> Thanks guys >>> The yeti >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Nighthawk Motorcycle Lovers!" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> To post to this group, send email to [email protected]. >>> Visit this group at http://groups.google.com/group/nighthawk_lovers. >>> For more options, visit https://groups.google.com/d/optout. >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "Nighthawk Motorcycle Lovers!" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To post to this group, send email to [email protected]. >> Visit this group at http://groups.google.com/group/nighthawk_lovers. >> For more options, visit https://groups.google.com/d/optout. >> > -- > You received this message because you are subscribed to the Google Groups > "Nighthawk Motorcycle Lovers!" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/nighthawk_lovers. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Nighthawk Motorcycle Lovers!" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/nighthawk_lovers. For more options, visit https://groups.google.com/d/optout.
