leebherron Posted January 28, 2009 Report Share Posted January 28, 2009 Has anyone tried a 290cc big bore kit ? What are the pros and cons ? Is rejetting a must ? How would you make the airbox bigger? Does it help low speed chuggin' ? Would a 13/1 compression piston work? Quote Link to comment Share on other sites More sharing options...
arnoux Posted January 28, 2009 Report Share Posted January 28, 2009 We have used an Athena 290 big bore kit. Very good. Big increase in bottom end No minuses, unless you count trying to hang onto the bloody thing when it hooks up. Some rejetting required. No change to Airbox. need to run a couple of head gaskets to keep compression the same. Quote Link to comment Share on other sites More sharing options...
grabasarni Posted January 28, 2009 Report Share Posted January 28, 2009 How do u find it grips with the 290 kit? Does it increase the engine braking? Quote Link to comment Share on other sites More sharing options...
leebherron Posted January 28, 2009 Author Report Share Posted January 28, 2009 Hi Paul ! Does S3 Products make a more affordable (than the Mitani) , Ti headpipe for the Scorpa 250F yet ? I have removed the inner muffler tubes and cut down the air filter cover on my 07 and have more engine response and less engine braking ! Do any of the aftermarket idle screws fit the Scorpa pumper carb? Quote Link to comment Share on other sites More sharing options...
arnoux Posted January 29, 2009 Report Share Posted January 29, 2009 Hi Paul ! Does S3 Products make a more affordable (than the Mitani) , Ti headpipe for the Scorpa 250F yet ? I have removed the inner muffler tubes and cut down the air filter cover on my 07 and have more engine response and less engine braking ! Do any of the aftermarket idle screws fit the Scorpa pumper carb? S3 do not have aheader for it yet as far as i know. The idle screw can be changed on the carb, BUT.... it does not fit on the SY250F, not enough clearance between the carb and chassis rail. The 290cc big bore kit does not increase the engine braking. S3 now make a nice big bore kit for the Yamaha 4 banger. Also Vertex do a 300cc. Quote Link to comment Share on other sites More sharing options...
ahamayfrank Posted January 29, 2009 Report Share Posted January 29, 2009 I am half scared to respond in the Scorpa Forum, but the Bad Mood Beta guys have stayed away so far in this thread. Not sure why some are so grumpy, or dislike Scorpas so much, but! I too have an Athena 290cc kit installed on my SY250F. My findings are similar also with the power increase. Much better low end but I feel some boost all the way up through the rpm range. Looking at the parts CD you can see that the stock setup uses 2 base gaskets and mine had 2 also when I disassembled it. According to the Athena information the compression ratio is the same as stock with the 290cc kit so I installed 2 base gaskets when I reassembled mine. I cannot detect any change in compression braking, starting, or any increased stalling. As a side note, after learning to always apply a bit of throttle when catching your balance with the clutch when stopped, I stall the engine very, very infrequently with 250 or 290cc. I changed to the 2008 carb at the same time and increased the pilot jet one size and like to run the fuel screw at 2 turns out at normal temps. Another advantage to the Athena kit is better cooling. I feel the bike runs a good bit cooler with the increased water jacket size. I think all the 4-strokes run warmly, so this was an unexpected plus! I also have a Mitani Titanium head pipe. I ordered it from a dealer in the UK and with the favorable US exchange rate it ended up just a few $ less than a stock one. It came with a Carbon Fiber heat shield that is very fragile (looks cool though) and the shield mount brackets are thin so can bend easily when hot. I put my stock heat shield back on and carefully selected the mount bolt length to assist the flimsy brackets in supporting the shield. Love the bike. Frank Quote Link to comment Share on other sites More sharing options...
leebherron Posted January 30, 2009 Author Report Share Posted January 30, 2009 Hey Frank, you didn't need to up the main jet with the big bore? Did you get any takers on your's yet? I took my carb apart tonight and the jetting was the same that The Hell Team recommends! Just don't tell anyone how hard it is to get the air boot AND exhaust on at the same time. I ended up taking the head pipe off. P.S. Scorpas rule, Betas drool ! Quote Link to comment Share on other sites More sharing options...
ahamayfrank Posted February 10, 2009 Report Share Posted February 10, 2009 Lee, It is possible to remove the carb without taking off any of the exhaust. Remove the Quote Link to comment Share on other sites More sharing options...
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