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MG MGB Technical - HIF Needle choice

Hi.

I'm the proud owner of a 1973 MGB GT running on HS4 carbs. I've decided to update and bought a complete set of used HIF carbs as from the 1974 model.My engine is overbored to 0.040''. I've got a fast road cam, lightened flywheel, raised slightly the compression and 2 big K&N air filters.
Can you help on this:

1. I guess the standard needles (AAU?) that come with the carbs won't do the job. What do you recomend?
2. Are the needles interchangeable between carbs (HS and HIF)?
3. Any other concern before I do the carb update?

Thanks a lot!

Valter.
Valter >´99 VVC & '73 BGT<

In my humble opinion, HS4 carbs are better wich HIF4, the temperature compensator in HIF it's a bad idea. Peter Burgess say AAA biased with KN and engine modified, biased needles are interchangeable HS to HIF.
Regards
michel

Thanks!

What do you mean by better? More reliable? I've been having lots of trouble with floats and jet leaks on the HS4s. HIF4s don't have a remote chamber, so must be better on this.

I think I've got a pair of AAA needles for the HS4s. So I can swap them, right?

Valter.
Valter >´99 VVC & '73 BGT<

Michael- The new millenium strategy for nailing the proper needle for your HS carbs is an Innovate LM-1 run showing the AFR through the range, then distilling the results to a 1/8th increment chart readout using the SUneedle programs available free on the web, and matching a needle to it. For example, we started with a more or less "Stage II.5" engine like yours using a BAF needle on the 1 3/4 HS6 and mapped it's AFR through the range using the Innovate. Then, using the SU needle program "Design a Needle" chart, input the AFR per stage compared to the existing BAF needle and found it was upside down: the firt 6 stages were too fat and gave lean reading, and the back 7 were too skinny, making 7 and 8 on the AFR between 2500 and 5500 rpm. We selected a BCC which, on paper, should have given us slightly lean, 15-17 AFR, initially and at cruise, but slightly power rich , 12-13, at WOT and high RPM ranges. We installed the new needles and ran the AFR. Guess what, it read like a book, exactly matching the projected AFR at each one of the 14 stages. Hey, thatis one satisfying way to get her done right. Also, the base set for the jets is so ez with the AFR, tuned to 1/4 turns of the hex nut for your exact desire at idle. Cheerios, Vic
vem myers

This thread was discussed between 28/05/2007 and 31/05/2007

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