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Post by flames on Jul 20, 2013 12:24:02 GMT 1
hi peoples,having a bit of a prob with the running of my bike,which would appear to be carb related.it appears to start as the needle taper comes into play.runs good from idle,then when the throttle reaches the point where the needle tapers,there is a loud kind of bwooaaaarrrr noise which sounds like it is coming from the airbox,tho i cant swear to this,it could be engine noise.when i have the needles set on the middle clip it starts around 5k,i read on here that a bwooaarr noise is normally associated with running weak,so i raised my needles to the top (clip in bottom notch).this has moved the ruff running from 5k to 6k.if i open throttle hard from this area it seems to bog ever so slightly before it builds revs,which i think would suggest it is running rich in this area? from 7k to the redline it pulls hard,which suggests the main jets arent too far out.its just the taperd area which seems to be causing probs.the bike has just been run in,i havent done a proper plug chop as yet,because of this rough running.my motor has had a hunger for pistons recently,and dont want to give it big beens until this prob is sorted.which also rules a dyno run out until it runs a bit better.
so has anyone any ideas as to whether she is running weak or rich?
whether new needles would be worth a try? and if so should i try some with a different taper?
whether going up or down a size on the main jet would worth a go?
im unsure as to which way to go,because the symptoms seem to suggest she is running weak and rich.but it only starts when the taper starts.im guessing when it smooves,coincides with when the taper straightens out.
as always,any help or advice on what to try will be greatfully recieved.
thankyou
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Deleted
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Post by Deleted on Jul 20, 2013 13:18:57 GMT 1
what carbs do you have on it and which needle, pilot and main jets?
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Post by flames on Jul 20, 2013 14:09:14 GMT 1
its 250 carbs,4l1 00.however it has 350 internals.it ran sweet as a nut with these on when i first had the bike,so i know they work,but at 18,i was too naive to make a note of how they were set up.mj's are 220,5k1 needles,with wotever slides the 350 should have.(checked with haynes and they tally up)pilots are 22.5 iirc,as per 350.mite try locate set of proper 350 carbs and go from there.its annoying tho,as i know these can work,and i have other things i would prefer to spend me hard earned on than a set of carbs,that wont even guarantee to sort the prob.i marked the throttle position,where it all starts and checked carbs (with them removed).this is how i worked out it starts with the taper of the needle.
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Post by oldelsieboy on Jul 20, 2013 14:19:39 GMT 1
The internal air jet, which is machined into the body of the carb so cannot be altered, is different between 4L1 & 4L0 carbs.
OEB
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Deleted
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Post by Deleted on Jul 20, 2013 14:21:19 GMT 1
Carbs are the work of the devil. My Steve baker Lc ran fine went round silverstone and then it got parked up from October to march. Then the bleeding thing wouldn't go very similar to yours. Tried everything and still the same so took the carbs off my Jenny Roberts and she was fine again.
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Post by flames on Jul 20, 2013 16:41:15 GMT 1
The internal air jet, which is machined into the body of the carb so cannot be altered, is different between 4L1 & 4L0 carbs. OEB cheers,i know the internal airjet is differant,but it did work with this set up before,but as mick says,his was ok to start with,then played up.so maybe there is something in it.however the problem starts from around quarter throttle,maybe between 1/4 and 1/2 throttle which coincides with the taper on the needle.i thought that by the time the taper of the needle comes in,the pilot circuit is bypassed? from idle to 1/4 throttle is responsive and runs fine.pilot runs from idle to around 1/8 throttle? if this is the case,my poor running is caused by a differant circuit in theory? as i said before going from throttle position with the carbs removed the problem starts as the needle taper comes into the carb body.i have altered a few things from how it was set up before,i have 6mm spacers fitted,and pv rubbers and balance pipe fitted.(wings removed as i still run lc reed valves).im thinking i just need to get the needle heights and the main jet matched to work together as they cross over. if i am wrong about the pilot circuit being bypassed over 1/8 throttle please correct me,if pilot is still involved it could be that the changes are too much for the 250 internal jet. |
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Post by Delbert on Jul 21, 2013 9:01:51 GMT 1
As oeb says they are different ,, I run 250 /4l0.01 carbs on mine. These wont run correct either with 350 internals ,, after much work I came up with this ,, 22.5 pilots , 180 mains , 5k needles with clip second notch down from top . Mine runs sweet as , hth
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Post by flames on Jul 21, 2013 19:46:16 GMT 1
thanks mate,mite give smaller mj's a shot.got 220's in at mo,clip in bottom notch with airbox lid removed,she flies,and put front wheel in the air.but there was a flat spot in the 5n arf region til power cut in.when I moved the clip up 1 notch with the lid on,i got good pull from 30mph in top gear (2.5k).got a pair of 185 and 240 mj's,so will probably have a good play around tommorro while kids at school and mrs working.
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