twinning Posted June 12, 2014 Report Share Posted June 12, 2014 Hello this is my first time posting this site has been real good reading. My ride is a full rebuilt +4mm 421 cub mild porting vforce4 reeds pro design intake 35mm airstriker carbs running pump gas here in oz which is 98 octane with Yamaha oil at 30:1 pipes are fmf powercore 2 . the carbys came with 48 pilot 160 main and DEK needle ive tried 45 and 42 and now am on 40 pilots my problem is its still doughy down low and threw the mid . I had more mid power when on 42 pilots with the clip on its leanest but was still doughy down low which is why I swapped to 40. Any thoughts I'm thinking the CEL needle may help the mid but am lost on the bottom. any replys much appreciated . Quote Link to comment Share on other sites More sharing options...
dirtydownunder Posted June 12, 2014 Report Share Posted June 12, 2014 Are you comparing to a stock cylinder ? 421 cubs don't have the best bottom end. They are top end orientated. What do the plugs look like after a good run ? Tried 158s ? Quote Link to comment Share on other sites More sharing options...
twinning Posted June 12, 2014 Author Report Share Posted June 12, 2014 Thanks for your reply I'm not really comparing it to a stock cylinder just saying how it is. I have got 155 mains to try although I don't think its the main I'm more thinking the needle and clip as this has more to do with the mid range power I think ? waiting on the CEL needles but in the meantime was thinking going 38 on pilots ? any thoughts ? Quote Link to comment Share on other sites More sharing options...
twinning Posted June 12, 2014 Author Report Share Posted June 12, 2014 Plugs still oily. Quote Link to comment Share on other sites More sharing options...
dirtydownunder Posted June 12, 2014 Report Share Posted June 12, 2014 mid range as in mid rpm or half throttle ? wide open throttle, mid rpm could be needle or main half throttle could be needle, pilot or main if your plugs are black and oily after some wide open throttle pulls, then ya main is rich. what size domes are you running ? Quote Link to comment Share on other sites More sharing options...
2sTrokeLove Posted June 13, 2014 Report Share Posted June 13, 2014 You will always have trouble with those carbs u need some regular pwks. Quote Link to comment Share on other sites More sharing options...
twinning Posted June 13, 2014 Author Report Share Posted June 13, 2014 Mid range as in half throttle there seems to be a big flat spot then at wide open throttle bang she finally opens up and screams like it should . not sure on the domes size will have to get them.I got smaller mains coming and CEL needles too. Also ordered some 158 and 155 mains. Your thought on the big flat spot in mid throttle ? cheers. 2stroklove ill give these a go before I buy new ones my budget blew twice already on this build. Quote Link to comment Share on other sites More sharing options...
dirtydownunder Posted June 13, 2014 Report Share Posted June 13, 2014 well a big flat spot to me, kinda sounds lean. does it splutter or anything or just die in the flat spot ? have you synch'd the carbs ? at half throttle the slides might be off. and at full throttle, be all the way open. but they would have to be pretty far out for a big flat spot. all needles/jets the same in each carb ? try the cel, in middle clip and see how that is. and make sure the carbs are synch'd. whats your elevation and are you in real cold/snow side of au ? Quote Link to comment Share on other sites More sharing options...
twinning Posted June 13, 2014 Author Report Share Posted June 13, 2014 (edited) The carbys are synched I use my eye and then check with synchroniser . all jets and needles the same.the flat spot is from about 1/4 to 3/4 throttle it sputters and chokes then after maybe 1 to 2 seconds and she opens right up. I'm located near port Macquarie NSW elevation about 50m. Its about 19 to 21 degrees during the day.humidity around 50%. Will try the CEL needles when they come in. Edited June 13, 2014 by twinning Quote Link to comment Share on other sites More sharing options...
dirtydownunder Posted June 14, 2014 Report Share Posted June 14, 2014 spark plug caps can cause some spluttering also. get multimeter and ohm the caps, they are 5k ohm caps, so should test under that. if they good, cut like 20mm off the plug lead and re screw back on, if not good replace the cap and do the same to the plug wire. poor/incorrect dome design can mess things up too. for pump 98 fuel, the domes would wanna be around 23-24cc for shelf domes. youre not running an aftermarket cdi or stator are you ? checked the pickup gap clearance at the flywheel ? Quote Link to comment Share on other sites More sharing options...
twinning Posted June 14, 2014 Author Report Share Posted June 14, 2014 Domes are 23cc according to Tony at TDRACING who i bought basically half the gear off he was aware of the fuel I would be using. Ignition is new Stator is old original CDI is old original. The leads on new ignition are really long so ill try the ohm test and see if that helps. Quote Link to comment Share on other sites More sharing options...
twinning Posted June 14, 2014 Author Report Share Posted June 14, 2014 Ok so the leads were no good I chopped off about 50mm and redone tested good . bike sounded better but its started too rain here for the first time in 3 months and I'm not game to ride in the slippery shit. Lol. Will give a squirt tomorrow . thanks for your help so far cheers. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.