So I fitted some su's (HIF's)on my 3.5 V8. They ran fine but where peeing fuel out the overflows at idle.
Had them appart, checked floats for holes etc etc put back togeather, fitted a sytec fuel pressure reg and set to 2 psi, and replaced the needles but then it wouldnt start.

Had them appart again & Float Heights where wayyyy out so reset to approx 1mm.

It'll now start with quite a lot of encouagment and foot flat to the floor.
It will rev up slowly, but if you blip the throttle it just bogs out, backfires and then dies if you dont life off the loud pedal??

Double checked timing and its spot on. I played with the mixture and found a setting where it will run best, but much adjustment away from that just makes it run worse.

Its almost like there is an intermittent fuel delivery issue rather than mixture....

Any ideas very much appreciated as been playin about with this all week now, and ive managed to coax it into life eventually but now still not right!

sorry should say LIFT not LIFE

Hi Eddyendo,
I have SUs fitted and they started behaving like you mentioned: backfire / bog / die etc. Needed lots of choke to pull away smartly from a junction or accelerate, so they were obviously running lean. Turned out to be the throttle spindles letting air in, so mix goes lean on acceleration due to the vacuum. The air flowing in through the spindles doesn't lift the needle so mix goes lean.
A way to test for this is dribble some light grease around the throttle spindle and start the engine, give it a few revs and see if the oil gets sucked in or if it just stays there. Amusingly, I just got used to having to pull the choke out every time I wanted to accelerate strongly. Can't believe I used to do that now !

quick check - have the dashpots got oil in em?

you could pull a plug and see what it looks like.

Could be the crankcase breather pipes have a split in them or letting air in somehow.
Check where they fit on to the carbs that they are not perished or split.

Could disconnect them and block the tubes on the carbs and see if it runs better.

Also make sure that the needles are seated propper in the pistons (if you have had them off) if not seated proper thay will run lean.

Shut off needles in the float chambers may not be set proper either.

Does it rev ok if you spray fuel in with a hand spray thingy from the kitchen, could be electrical

May be not but best to eliminate

I have a pdf manual for them , pm me your email address if you want it!