I rebuilt the HIF6s after I got them. Cleaned and inspected them. I had them back apart a few times looking for issues. Checked the float level a number of times and again just the other day. Changed out the fuel pump. Ran pony tank right into fuel pump to eliminate the gas tank and line up from it. Not saying I haven't missed something.

I was searching web and found some articles about HIF6s and needle issues on MGs. And one awhile aback in this forum.

http://www.brickboard.com/RWD/volvo/1066674/120-130/hif6_carbs_b18.html

More info (MG I think):

I replaced the "BAL" needle with the "BEL" one. At idle I couldn't get the motor to run without choke or I had to have the idle screw turned down (faster rpm"rpm's) so it won't stall. The CO2 analyzer showed a CO of <.6%. NOT GOOD. I screwed the mixture screw as far as I could and managed to get the CO2 up go 1.5%. Way, way to lean. Switching back to the "BAL" I was running around 1.6% at base line and adjusted the mixture screw to between 2 and 2.5%. Idles better, etc."

And more (MG I think):

1-3/4" SU HIF6 carb rebuilt with "BDL" Needle - good for stock 1275 engines. For 1380's, we recommend changing the needle to a "BDK" (I have a HIF on my 1275 and I started with a BDL but seemed too lean at speed so went with BDK now is perfect.

It looks like people were having issues getting the HIF6s dialed in for an application they were no on in the first place. Be interesting if someone on here could chime in if they have HIF6s running on a B18. And if so what needle there running. I have my mix set as rich as I can and I think it wants more. Unless I still have an unfound vac leak. The cold start issue might be related but unknown as yet. I'm going to double check the fuel delivery again.