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MG MGB Technical - HIF 6 Needles ans Springs

Hi,

I have just build a 1860 engine with HIF 6's, a piper 285 cam and a Peter Burgess Head. The HIF 6's have BBW needles and Red Springs.

The mixtures even with the carb set to full rich is still running lean.

Please could someone tell me what the correct needle and spring setup for the engine configuration?

Thanks

Jules
J Wale

You have a Burgess head, ask him!
Mike Howlett

Hey Jules- There's a great program downloadable gratis on the SU needles: Minty SU Needle Compare-o-ramawww.mintylamb.co.uk/suneedle. You can see where you might correct the overlean. Do you have an AFR, or access to one? Really you need to tune the mix for running not idle. I'm with BAC on pretty much the exact same setup: Burgess FRBV, P285, 60 over, although I advanced the cam 48 and am using the 1.6:1 Harlan rollers.
You'll notice the BAC crosses over from your BBW and starts getting richer between stage 8 and 9, half way down the needle. Although an onboard Innovate AFR can be had nowdays for under $300, you can always use the tailpipe sniffer mobile model borrowed from friend or club member and note the actual burn at 2500, 3000, 3500, 4000, and 4500. This is where the rubber meets the road and the only AFR ( mix) numbers you need to fret over. Of course and hour on the dyno, under load, is the best world of all. Idle mix AFR is forgettable if it's below 20 or so, as most all needles are close at stages 1, 2 and sometimes 3. So a BAC will give you about the same AFR as you BBW.
In closing, let me say port vac on the HIF 6 will give you a higher idle advance allowing 2 things: 1. The idle can be set down to 500 if you like and 2. The vaunted lope everyone snivels about on the P285 HR is hardly noticeable, and certainly not an engine rattling lumpity lump. I love this cam and bought my first from Peter 12 years ago and am still running it. The mid-high end pulls like a tractor. Cheers, Vem
vem myers

Well, excusseee meeee. I really meant to say "MANIFOLD" vac above. Unless someone drilled in the ports, the HIF use the manifold vac with the dizzy advance diaphram specific for that setup--- different from the dizzy vac used for port advance donchaknow. Cheers Vem
vem myers

The difference between manifold vacuum and carb vacuum is purely for emissions at idle. Any distributor will run with either vacuum source, the only difference is at idle. Manifold vacuum is near max at idle, carb vacuum is zero. As you start to open the throttle the two very rapidly converge. At all usable throttle openings the vacuum signal is identical. http://www.mgb-stuff.org.uk/ignitiontext.htm#vac

The distributor centrifugal and vacuum advance curves are to give particular responses from the engine. North America had loads of different distributors in an effort to keep abreast of the continually changing regulations. the UK only had one distributor for the whole of rubber bumper production, even though the vacuum source changed in September 76, and even though HIF carbs had been in use since 1973.
PaulH Solihull

Jules- Epiloque?

vem myers

Jueles,

I have built a similar engine and tested out that the BDR needles worked best with the HIF 6 carbs. Red springs are O.K. for normal street use.

Engine specs: 1868ccm, flat top pistons, 285/2 cam, ST dizzy.

Ralph

R.S. Ralph Siebenhaar

Hey Jules, so the story continues? Vem
vem myers

This thread was discussed between 26/11/2012 and 06/01/2013

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