11 replies to this topic

[Big_Adam]

Evening.

right rebuilt my carb a few days ago and did a few things to the spindle to get more air into the engine. now i have a little problem.

At around 4000rpm theres a HUGE flat spot just gets to about 4000 odd then screams for a bit then keeps carrying on up the rev range. now i know the idle mix is ok (lift pin) but that top ends a bugger. BUT if i pull the choke out going full wack then El Gordo will power thro very happily.

so should i file my needle to account for the extra air flow; and if so which part of the needle. from the vizard book i see that the 1st inch or so of the needle is for idle and cruise speeds then top end is whatevers left. so i know i would need to file a bit off the end.

but do you file the side (ie not the side thats rubbing agenst the carb beacuse the needle is spring loaded) or off the bottom of the carb,

I'm getting a new needle (AAA) soon as i'm fitting a new exhaust soon so if i do screw this up i should be ok.

just need a little guidence is all.

cheers,

[Purple Tom]

The only successful way I've seen it done is using a drill chuck in a bench grinder and a very fine, thin piece of emery used to remove material from the section of the needle that needed to be richened - AC Dodd did it when he tuned my twins for me.

The needle is then obviously mounted in a very fast spinning small lathe and allows you to modify it uniformly. However you need to know what you're doing as literally 0.0010" from a needle will make a big difference to the performance of the engine.

On no account should you use a file and just remove material from one 'side' of the needle, I've seen this done before and it just does not work, just buggers things up even more.

I couldn't advise where on your needle you need to modify - when I've had similar problems in the past I've been on WinSU and spent time comparing needles to find one thats the same where it needs to be but richer/leaner in the section where it needs to be. it usually worked quite well that way, although at £7 a needle its expensive!!

Hope the helps a bit.

Tom

[miniboo]

filing needles is a specialist job i think. well, to gtet it right. i would say speak to AC Dodd who will do you you a custom needle perfect for your engine. a new needle is onlyabout 7 or 8 quid and it wont be much more to get a custom one done.

look here: http://www.mlmotorsp...wtopic.php?t=17

[Big_Adam]

ah well i'll leave it then for now.

i mean i got the AAA needle coming and its only really a problem when i'm giving it the berrys. then i can just pull the choke out.

Cheers guys.

[Guess-Works.com]

never had a problem filing needles, with a set of needle files believe it or not, the needle does not need to be round, but what you need to avoid is sharp steps which may prevent the piston dropping when on idle..

Filing it in the right place and the right amount is the art !

When you have something which is working right, you are then better looking for a needle which will match the profile you have invented.

Edited by GuessWorks, 09 October 2006 - 01:25 PM.

[fikus01]

i would have said the emery cloth and drill method would have been the best!! and i'd only do it to the lower half of the needle!! do it a bit at a time and have a go with a little drive!! then try again!! i have done this at the roadside stopping every now and then and removing the dashpot and getting out a battery drill and emery to mod before the next run!! was a fun packed day!!

[miniboo]

I tell you what!! ihaving read this i might have a go with a spare needle i have knocking about!

what grade and type of paper is best to use?

[fikus01]

300 grit?? i relly dont know!! nothing too harsh as you only want to remove a little bit here n there!! just a point if ur doing the driving method like i did dont go too far from home!! long walk back if u drop something down a drain otherwise !!

[miniboo]

is that talking from experience????

[fikus01]

i dont know what you mean!! i dropped the needle spring!! ok it ran but was all over the place as the needle wasnt in the same place at the same revs all the time!!

:'(

[minipip]

HA HA HA LOVE IT! that was brillint always wondered what it would run like without the spring lol!
what would it run like without the needle????? or is it something not to try?

Edited by minipip, 09 October 2006 - 09:48 PM.

[fikus01]

overfuells massivly and only runs at full throttle!!! plumes of white smoke out the back!!