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 Post subject: Carb needles...again..
PostPosted: Sat Jan 15, 2022 7:20 am 
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848cc
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Joined: Fri Mar 30, 2018 7:21 pm
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Hi All,

Does anyone know of a needle with the top end somewhere between a 7/CP4 and a BG?

I've been doing a lot of dyno and road testing. #6's were great at all cruise speeds/loads but went way lean above 5k. I skimmed them down to something close to a CP4 and 7 (and beyond) at the top end and it's getting better but those needles are a bit untidy now, so I'm looking to start again with fresh needles closer to what it wants.

I'd love to try a BG, but it's a big jump from a 7 so it could turn out to be too rich and I'm getting sick of buying needles :)
So something a bit thicker I can mod if required would be great starting point.


Any ideas?

Thanks!


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PostPosted: Sat Jan 15, 2022 7:41 am 
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Have you had a look at the Mk1 performance- Conversions Website?
There is a free to use Su needle selection tool in their Technical Section.
It's a very well put together piece of software and easy to use after some practice.
Regards
Glen


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PostPosted: Sat Jan 15, 2022 8:06 am 
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Hi Glen.

Yes I've been using that spreadsheet to modify my needles from 6-CP4-7 etc using the 'Advanced' tab, it's a fantastic tool.
But I haven't been able to make any sense of the 'Show Suggested' option on the 'Basic' tab. It only ever seems to suggest a AY needle, which is nothing like what I'm seeking. I'll play with it some more later and see if I can get it to make better suggestions.


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PostPosted: Sat Jan 15, 2022 4:51 pm 
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Have a look at an SS needle, or an MME. They seem to fall somewhere near your parameters.

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Cheers Dave.


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PostPosted: Sat Jan 15, 2022 5:20 pm 
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Thanks Dave. The MME will be a swinging needle, but I'll look at the SS, I've never heard mention of it before.


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PostPosted: Sat Jan 15, 2022 6:02 pm 
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Joined: Sun Nov 06, 2005 5:41 pm
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Location: Adelaide
ben73 wrote:
Thanks Dave. The MME will be a swinging needle, but I'll look at the SS, I've never heard mention of it before.


The MME is fixed, used to run them on the rally car - 1293, 649 cam and twin 1 1/2's. From memory about as rich as you can go.


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PostPosted: Sun Jan 16, 2022 7:49 am 
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Both are fixed 090 needles. In fact the MME may be the better choice for you.

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Cheers Dave.


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PostPosted: Sun Jan 16, 2022 10:17 am 
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Joined: Sat Mar 24, 2012 1:39 pm
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Location: qld
Hi ben73. Just for clarification for me..... you are running twin HS4s?

Have you tried pulling the bridge down a little to make it run richer throughout the range?

I had a 1310 motor with twin HS4s that ran #6s BUT on the road they would slowly lean out if you kept WOT for more than 20 seconds or so. I did slight mods on the last couple of stations on the needles( similar to you again)- AND i pulled down the bridge to fudge a little more richness ( albeit throughout all revs) Result - had to up the idle - made it sound mean just sitting at lights and still had good drivable AFRs - on cruise and importantly on WOT - (NOTE this was a weekend warrior - fun drive car so not flat stick for extensive periods) I used an innovate wide band AFR meter plumbed in just after the merged pipes and had it hard wired in for a while . This was a relatively tame cam though and i didn't have to worry about traffic and being too rich for long periods at idle.

How often are you planning on being above 5000rpm for extended periods of time?

I would also suggest checking the curve on your dizzy - i had a CSI 16 different curve dizzy and found the engine liked early advance ( 22-24 degree at 2000ish - but 30 overall)

Cheers Darryl


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