Rich or Lean idle?

[455bird]

What am I missing?  I've got a 69 Firebird with a 9.3 to 1 compression 455, a comp cams xe274 cam, 230-236 @ .050", 2004r trans, and 3.73 gears.  I've tried two different Q-jets and a Holley 3310 vac. sec. with the same results.  Carb #17056512 is on the engine currently, calibration is as follows: idle tubes - .0385, idle down channel - .055, upper and lower air bleeds - .070, idle bypass air - .1065, mixture screw holes - .1065, 75 jets, .044 primary rods. Carb was rebuilt with Cliff's kit using recipe #3 from his book.  The car has little to no hesitation off idle, pulls pretty well at WOT, but idles like crap.  Idle is set at 700rpm in gear and pulls only 8-9 inches of vacuum. Out of gear it pulls 11-12 inches of vacuum.  Car sounds like it's loading up, RPM's drop, idle is very rough, appears to have a miss or misses, and stinks to high heaven under the hood.  Burns my eyes like crazy.  No sign of nozzle drip, checked float level twice, 1/4 inch, no flooding.  Ignition is HEI distributor with MSD Digital 6 box, 12 degrees initial, 36 total, all in by 3600rpm, ported vacuum.  APT is 3.5 turns out, and mixture screws are 3 turns out.  So, am I running rich or lean?  Hydrocarbons at idle will climb up to 5000 ppm!  Sign of multiple misfires?  Any ideas?

[77cruiser]

Try upping the timing to see if it helps the idle. Go up to 20 if it works you'll have to recurve your distributor.

[Cliff Ruggles]

Could be a fundamental problem not related to the carburetors.  Those cams idle "quirky" anyhow, from what I've seen, and 110LSA doesn't help much.

I've had several Pontiac builds in here to tune with XE cams in them, and not the least bit impressed with any of them.  Noisy valve train, quirky idle, and not very impressive for power production.....Cliff

[73ss]

Are your plugs gapped wide for the msd? I replaced my plugs once and opened them up to .055 and my combo did not like it. Closed them back down to .040 and it just felt more crisp & responsive all the way around. I'm not an expert but it looks like you should have plenty of idle fuel. Based on your HC readings it looks like an ignition problem. I've seen several 6AL's over the years that were not up to snuff. Your's is a digital box so I assume it's fairly new? It's a pia but you could try a known good stand alone HEI and see if things improve. Ohm out your plug wires and look for any burned boots. It doesn't take much for it to jump to ground somewhere. Sometimes it is the basics that bite us.

I had the same XE cam in my 454 chevy several years ago and just like Cliff says, Noisy valvetrain, stinky, crappy idle, poor vacuum. Swapped it out for a old school 114 lsa grind, Night & day difference.

[455bird]

I've already tried more timing.  It did speed up the idle a little, but it still ran rough and had the smell, and it pinged at part throttle and at WOT.  Plugs are gapped at .045", tried .030" as well but it made no difference.  Yes, the MSD 6al2 digital is new.  Plug wires are new, ohm checked them before installation just to be sure.  All were good.
So Cliff, what cam would you suggest?  I do have a new 041 cam and Rhoades lifters laying around in the shop.  Do you think I have enough compression to make it work?  Also, the heads are ported #13's.  They flow 255cfm on the intakes.

[77cruiser]

How much more timing did you try, did you recurve to dist. so it didn't over advance in the upper rpm's?

[Cliff Ruggles]

I've used the 041 cam with 6X-8 heads on 455's, and Rhoads lifters.  It actually worked pretty well, but they really shine with higher compression.

For sure I would NOT use a Comp XE cam in one of those builds, not enough seat timing and LSA too tight, they don't have a fighting chance of making great power or working well anyplace.....IMHO.....Cliff

[blazer74]

For what its worth I have a 110lsa 268 cam in  sbc and I have to go from 3 turns out best idle to 4.75-5 to get the stink out of the idle. I have a good idle either way.