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Post by bigdazbandit on Dec 21, 2014 14:31:38 GMT
Hi all need some help I have a mk1 b12 running 150 jets seems to have a flat spot in second gear about 3000rpm my friend is jetting his and wondered what jets you'd all suggest both running twin upswept exhausts and k&n pods
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Post by oilyspanner on Dec 21, 2014 15:49:04 GMT
Have you got a kit, or just changed the main jet Daz ? The region you have trouble with would be pilot/needle affected - have you turned the pilot screws out ? or lifted the needles up to enrich the mixture ? Really a larger pilot jet needs to be fitted and a more aggressive needle (thinner) to combat the big changes.
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Post by kokolis on Dec 21, 2014 15:53:34 GMT
3k rpm is still on the low circuit. Try mixture screws on 2,5 turns out
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Post by katana on Dec 21, 2014 18:39:50 GMT
150's are way over size IMO - you'd require more engine mods to need them - 1216 or head/CR or cams ie loads more air!
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Post by bigdazbandit on Dec 21, 2014 19:48:54 GMT
I bought the carbs off a chap on here it had the mains and pilots changed not tried the mix screws as yet I'm not too sure if it is a flat spot or the back spinning up need a dry day too give it a blast
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Deleted
Posts: 0
Reg: Mar 29, 2024 0:47:43 GMT
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Post by Deleted on Dec 21, 2014 21:08:10 GMT
daz be a man and fit sum flatside,s . evan more power ? then sell me them carb,s ok.
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Post by bigdazbandit on Dec 21, 2014 21:25:34 GMT
Lol not got flatside money's Dave
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Post by oilyspanner on Dec 21, 2014 21:50:13 GMT
Check the float heights too Daz, too high or low will have a big affect at the bottom end - always best to check your way through newly bought stuff. When you blip the throttle do the revs hang up for a while (lean), or fall below idle and the engine wants to stall (rich). A lean condition feels very hesitant and lurchy before going - too rich and the mixture is hard to burn - little power and then clears. The pilot jet could be too large if it's been changed. Too lean and you get a lot of exhaust popping on the over-run.
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Post by bigdazbandit on Dec 21, 2014 22:07:29 GMT
Doesn't feel hesitant but has a lot of popping when I let off balanced carbs last week as well
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Post by bigdazbandit on Dec 21, 2014 22:10:34 GMT
If it's popping it's too lean ?? So how do I rectify it sorry not all that clued up
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Post by bigdazbandit on Dec 22, 2014 6:00:51 GMT
Took it out this morning as its dry and it pulls to 3k open throttle and it coughs and splutters surges the cough again no power
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Post by oilyspanner on Dec 22, 2014 9:38:56 GMT
Ah, no that does sound at point the needles start to come in - as intake increases, the needle rises. Does it continue being jerky in the 1/4 - 3/4 throttle zone ? - if it were pilot jets, you'd have problems right at the start of throttle opening and whilst cruising - jerky and unpleasant. Try lifting the needles up a notch or two - you normally have to change the needles for stage 3, they might be standard ones, if you look at the top of the needle you should see the type marked on them, if you tell us what you have we'll have a good idea what's in there. Try lifting the needles up first.
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Post by bigdazbandit on Dec 22, 2014 17:35:42 GMT
It's ok thanks for all your advice chaps it hasn't been dyno jetted as I was advised just had a 150 main jet put in nothing else so ordered a full kit
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Post by oilyspanner on Dec 22, 2014 18:03:56 GMT
That's the easiest way to do it - easy to do main jet and pilot - but damn hard to get the mid-range, needle part right on your own.
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Post by bigdazbandit on Dec 22, 2014 18:53:43 GMT
I have a special weapon my best mate is a whizz of a mechanic let him do it lol
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